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446 Cards in this Set
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(MIDII #1)
What is the “magic bullet” for tuberculosis that was discovered in 1952? What short course treatment regimen followed in 1970? How is tuberculosis treated now? |
With the advent of streptomycin the late 1940s and INH in 1952, TB became curable! INH is the magic bullet for TB. Rifampin followed in the 1970s.
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(MIDII #2)
Discuss the history of tuberculosis. |
TB was not a significant problem until the 17th and 18th centuries as urbanization and crowding in unventilated living conditions increased, but by the 19th century with industrialization, TB caused ¼ of adult deaths in Europe. Koch discovered the TB bacillus and generated the “germ theory” of disease. Prior to the discovery of antibiotics, TB was treated with sanatorium regimens and rest. Patients were ordered to have fresh air and sunshine on rooftops and solaria.
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(MIDII #3)
Discuss the epidemiology of tuberculosis in Asia, Sub-Saharan Africa and Europe |
Mycobacterium tuberculosis infects 1/3 of the world's population. Causes 2 million deaths per year, 2nd only to HIV as a cause of death from infectious agents worldwide among adults. The relationship between TB and HIV has exacerbated problems, with TB increasing in areas with high AIDS incidence, particularly sub-Saharan Africa. (1) Absolute numbers of cases of TB are highest in Asia where the population density is highest, BUT (2) Case rates are highest in sub-Saharan Africa: 300 per 100,000 estimated incidence rates in sub-Saharan Africa vs 100-299 per 100,000 in Asia. (3) In Europe, 10% of infected people develop active disease and only 50% of cases are cavitary (cavitary cases are infectious). Each cavitary case needs to infect 20 to maintain the constant rate of cases. Better living conditions are less conducive to airborne spread.
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(MIDII #4)
Discuss the epidemiology of TB in the United States. |
The US saw a steady decline of TB until 1984 with a slowly increasing incidence. Causes: (a) neglect of TB control programs; (b) increase in urban homelessness and resultant crowding in homeless shelters; (c) advent of AIDS epidemic among this population. Restored TB control program funding and decreased crowding of the homeless means that the highest background rates of TB are among immigrants from high prevalence countries. 50% of the cases in the US are among foreign born. New York, New England, and the west coast states all have greater than 50% of cases foreign born as of 2003, with 300 per 100,000 estimated incidence rates.
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(MIDII #5)
Discuss the organisms responsible for causing tuberculosis. |
Mycobacterium tuberculosis complex includes several species, all derived from a soil bacterium: (1) Mycobacterium tuberculosis; (2) Mycobacterium bovis, which is found in unpasteurized milk. There has been a recent rash of cases in the US among immigrants who have favorite cheeses made from unpasteurized milk sent to them from home, particularly Mexico and the Dominican Republic; (3) Mycobacterium bovis-BCG is used to treat bladder cancer; (4) Mycobacterium africanum and Mycobacterium canetti are rare causes of TB in Africa; (5) Mycobacterium microti is a pathogen for rodents.
The organisms are aerobic, non-motile, non-spore forming bacilli. They have a high cell wall content of high molecular weight lipids (mycolic acid). They have a SLOW GROWTH RATE, with a generation time of 20 hrs vs. E.coli's generation time of 20 minutes. Takes 3-8 wks for growth on solid media. This has implications for length of treatment for complete sterilization compared with most bacterial pathogens (in other words, it takes longer to kill M. tuberculosis b/c it reproduces so slowly.) |
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(MIDII #6)
Discuss the TRANSMISSION of infection with MYCOBACTERIUM TUBERCULOSIS. |
Lungs are the portal of entry (except for M. bovis in unpasteurized dairy products from other countries). Transmission of TB requires inhalation of droplet nuclei (bacillus 5 microns) from an infectious person with active pulmonary tuberculosis (NOT just positive PPD). COUGH is most efficient at 3000 infectious droplet nuclei per cough. TALKING: similar quantity over 5 min. SNEEZING is more efficient than coughing; SINGING is intermediate between talking and coughing. The INOCULUM SIZE is relevant. TB can be transmitted in the autopsy suite from a cadaver: cutting thru lung tissue aerosolized millions of bacilli, and subsequent PPD conversion and progression to active TB is “astonishingly high.” VIRULENCE of the strain is also relevant. There was an outbreak of TB in Kentucky after minimal contact w/the index patient. The bacillus remains alive and infectious in the air for a long period. Ventilation is key in preventing transmission. Isolation of the patient is req'd as well as maintaining a mandated number of air exchanges in hospital rooms.
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(MIDII #7)
Discuss PRIMARY INFECTION with M. tuberculosis (BEFORE THE IMMUNE RESPONSE!!!) Is it possible to have reactivation of one metastatic focus (TB meningitis) without the others? Can you have TB meningitis without pulmonary TB, for example? |
The bacillus reaches the alveoli and replicates extracellularly in the alveolar space & intracellularly in the alveolar MΦs. There is a lack of immediate host immune response. The alveolar MΦ ingests the TB bacillus; the bacillus sits in the phagosome; the phagosome normally incorporates proton-ATPase into the membrane yielding ↓ pH & acidification within the phagosome; the acidified phagosome fuses w/the cell lysosome, exposing the bug to toxic enzymes. MTB prevents insertion of proton-ATPase into the phagosome so the phagosome never gets acidified and never merges with the lysosome. MTB multiplies for weeks, both in the initial focus in alveolar Mφs and in cells transported lymphohematogenously throughout the body. METASTATIC FOCI are well established in regional lodes (hilar, mediastinal) and then to tissues which retain the bacilli and favor multiplication, such as (a) apical posterior areas of lungs; (b) lymph nodes in the neck; (c) kidneys; (d) epiphyses of long bones; (e) vertebral bodies; (f) juxtaependymal meningeal areas adjacent to subarachnoid space. These will be areas of reactivation of disease in the future since the seeded organisms remain alive but dormant once the immune response occurs. Reactivation can occur in any of these areas of the body with or without reactivation in others: it is possible to get TB meningitis or “scrofula” without pulmonary TB.
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(MIDII #8)
Discuss the development of the immune response to TB, which requires an intact cellular immune system, including CD4+ T cells. |
The immune response develops 6-12 wks after initial infection with MTB. Alveolar MΦs infected w/MTB release IL-12 & IL-18, which attract and stimulate T lymphocytes (mainly CD4 cells). ALL people have a native population of CD4 cells which can recognize mycobacterial antigens that have been processed and presented by MΦs. When a CD4 meets a mycobacterial antigen presented by the MΦ it becomes activated (transformed). A transformed CD4 cell proliferates and produces a clone of similarly reactive T lymphocytes. When the population of activated lymphocytes is large enough, there is a cutaneous delayed reaction to tuberculin = tissue hypersensitivity = positive PPD test. (AIDS patients with low CD4 cell count cannot effect an immune response to tuberculin so you cannot use a PPD test on them). Activated CD4+ T cells release IFN-γ which stimulates MΦ phagocytosis and stimulates MΦs to secrete regulatory factors such as TNF-α, which is req'd for granuloma formation and increases the MΦ's ability to kill M. tuberculosis.
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(MIDII #9)
What happens if an individual lacks TNF-α with regard to the immune response to M. tuberculosis infection? |
TNF-α is secreted by macrophages and increases the macrophages ability to kill M. tuberculosis; it is required for granuloma formation.(1) In mice, blockade of TNF-α resulted in reactivation, high bacillary burden, persistent tuberculosis and death. (2) TNF-α KO mice infected with M. tuberculosis followed a similar course. (3)Anti-TNF-α agents for rheumatoid arthritis and auto-immune disorders cause reactivation of tuberculosis.
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(MIDII #10)
Discuss the PATHOLOGY of infection with M. tuberculosis. The tissue response to MTB infection depends on activation of MΦs with secretion of lytic enzymes which cause tissue necrosis. (1) What are EPITHELIOD CELLS? LANGHANS GIANT CELLS? (2) What occurs with SMALL antigen load and HIGH tissue hypersensitivity? (3) Large antigen load and high antigen hypersensitivity? (4) Large or small antigen load with NO tissue hypersensitivity? |
(1)EPITHELOID CELLS are highly stimulated MΦs. LANGHANS GIANT CELLS have fused MΦs oriented around tuberculosis antigen w/multiple nuclei lined up peripherally. (2) SMALL Ag load and HIGH tissue hypersensitivity produce organization of lymphocytes, MΦs, Langhans giant cells & fibroblasts -> result in a granuloma, a successful tissue rxn resulting in containment of infection, healing w/fibrosis, encapsulation & scar formation. (3) LARGE Ag load and HIGH tissue hypersensitivity produce few or no epitheloid cells or Langhans cells, disorganized lymphocytes, MΦs and PMNs and result in necrosis and caseation. Caseous material is acellular and inhibits multiplication of organsms due to its pH and oxygen tension but is inherently unstable, liquefies and discharges through the bronchial tree. This discharge produces a cavity in which TB bacillus multiplies to make population 5-6 logs greater than in noncavitary lesions. (4) Large OR small Ag load w/no tissue hypersensitivity produces few PMNs or mononuclear cells and HUGE numbers of bacilli. This is seen in AIDS patients w/low CD4+ counts. Implications for post treatment appearance of lung and chest x-ray in AIDS patients is a lack of fibrosis or granuloma.
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(MIDII #11)
CLINICAL SYNDROMES OF TB INFECTION: Primary Infection with Resolution |
This occurs in 85% of cases. Patient is asymptomatic or has a mild viral syndrome. Enlargement of hilar and peribronchial nodes at time of infection. On CXR there is a calcified granuloma, evidence that the tuberculosis infection was successfully contained. 6-12 wks later there is development of a positive PPD.
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(MIDII #12)
CLINICAL SYNDROMES OF MYCOBACTERIUM TB INFECTION: Primary Infection with Progression: (1)Progressive Primary Disease in Young Children (2)Primary Infection in Adolescence/Young Adulthood |
(1)PROGRESSIVE PRIMARY DISEASE: (a) Occurs in very young children (<5) who are unable to resolve the infection. Local progression w/mid or lower field pneumonitis initially, then dissemination, miliary pattern in the lungs and frequent CNS involvement. Almost always occurs in developing world countries were TB remains endemic. (b) TB PLEURISY is a hypersensitivity rxn to a small # of organisms which reach the pleura in primary infection, resulting in exudative pleural effusion. Cultures are negative b/c very few organisms are present. 90% resolve spontaneously but WWII studies of soldiers showed 65% relapse to active TB (pre-antibiotic era). TB pleurisy should be treated! (2) ADOLESCENTS & YOUNG ADULTS: Primary infection results in “adult type” upper lobe cavitary disease. Puberty influences tendency to apical cavitation soon after initial infection. 23% of those infected betw/15-19, 13% of those infected betw/ 20-24, and 4% of those infected from 25-29 develop cavitary disease. Only 2% of patients over 30 develop cavitary disease w/primary infection.
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(MIDII #13)
CLINICAL SYNDROMES OF MYCOBACTERIUM TB INFECTION: Primary Infection with Progression Discuss AIDS Nosocomial Outbreaks of Tuberculosis |
AIDS nosocomial outbreaks of TB occur in AIDS wards, homeless shelters and prisons. Occurs when an undiagnosed patient w/active pulmonary TB is hospitalized in an AIDS ward or a shelter for AIDS patients. All patients have CD4 < 50. The index patient coughs and infects the other AIDS patients. AIDS patients with no cellular immune function can't mobilize CD4 and MΦs to contain or kill the bacillus. Results in rapid dissemination or death if untreated. Blood cultures will be positive for M. tuberculosis. (Multi-drug resistant TB outbreaks killed many patients, resistance wasn't monitored.)
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(MIDII #14)
CLINICAL SYNDROMES OF MYCOBACTERIUM TB INFECTION: Reactivation In what percentage of infected individuals does reactivation occur? When does it occur and why? |
Reactivation occurs in 10-15% of all infected with MTB. Involves persistence of viable organisms following containment of the initial infection. Disease occurs years after infection when the cellular immune response is no longer able to contain MTB: (a) IATROGENIC => in transplant patients, immunosuppressive therapy for connective tissue disorders (autoimmune disorders); (b) IMMUNOCOMPROMISING DISEASES => AIDS, malignancies, end stage renal disease, cirrhosis; © MALNUTRITION; (d) OLD AGE => hypersensitivity and cellular immunity wane w/age; (e) UNKNOWN CAUSES => hormonal, stress (immigrants).
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(MIDII #15)
CLINICAL SYNDROMES OF MYCOBACTERIUM TB INFECTION: Reactivation Where does reactivation occur and what happens? |
Pulmonary location is the most frequent site of reactivation of TB, occurs in 85% of patients. The posterior aspect of the upper lobe is the focus where reactivation begins. [Due to increased O2 in the apices and MTB's aerophilia. Also possible that deficient lymphatic flow at the apices results in retention of bacillary antigen and a hypersensitivity rxn leads to necrosis.] There is a localized pneumonitis => the inflammatory response produces fibrin rich exudates into the alveoli, caseating necrosis, liquefaction. There is drainage into the bronchial tree with cavity formation. Cavities favor bacillary multiplication in HUGE amts, 5-6 logs > than # of organisms in non-cavitary lesions. There are 10^9 or 10^10 organisms per gram of tissue. Cavitary disease is the MOST contagious as the cough aerosolizes hundreds of thousands of organisms.
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(MIDII #16)
CLINICAL SYNDROMES OF MYCOBACTERIUM TB INFECTION: Reactivation Discuss extrapulmonary tuberculosis |
Viable organisms remain alive and dormant for years in all sites to which the bacilli disseminated during the primary infection. (1) LYMPH NODES => scrofula is the most frequent form of extrapulmonary TB. Usually affects the cervical or supraclavicular chain. Biopsy and culture are essential (fine needle aspirate usually smear and culture negative). (2) MENINGES => rupture of subependymal tubercle into subarachnoid space. Meningitis is most severe at the base of the brain causing a thick gelatinous exudate. Affects the cranial nerves as they exit. CSF exam is essential to make the diagnosis: low glucose, elevated protein, lymphocytic pleocytosis. (3) BONES => 1/3of cases of extrapulmonary TB involve the spine (Pott's disease): hematogenous spread from contiguous disease, lymphatic spread from pleural disease. Early focus is the anterior part of the vertebral body. Spreads to the disk and then to adjacent vertebra. X-ray shows anterior wedging of 2 adjacent vertebral bodies and destruction of the disk. A tender spine prominence on exam is called a GIBBUS.
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(MIDII #17)
MYCOBACTERIUM TUBERCULOSIS: Symptoms of Infection |
(1)SYSTEMIC symptoms are non-specific: fever, fatigue, night sweats, weight loss.
(2)PULMONARY symptoms include cough, productive or dry. Most patients have the cough but may ignore it for weeks. (3)HEMOPTYSIS: (a) Mild-moderate w/chronic blood streaking results from caseous sloughing or endobronchial erosion and is seen in advanced disease. (b) Rasmussen's Aneurysm: sudden massive hemoptysis results from erosion of the pulmonary artery and is the only TB emergency |
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(MIDII #18)
MYCOBACTERIUM TUBERCULOSIS: Diagnostic Procedures => SPUTUM staining and cultures: (1)Acid Fast Stain and (2) Culture |
**SMEAR POSITIVITY means AT LEAST 10,000 ORGANISMS/mL of SPUTUM** (1) ACID FAST STAIN: Acid fast implies mycobacterial species (note: nocardia is weakly acid fast) but many other species besides M. tuberculosis complex will be AFB positive (including Mycobacterium avium, kansasii, abscessus, chelonae). (a) ZIEHL-NEELSEN STAIN: fixed smear covered with carbol-fuchsin, heated, rinsed, decolorized with acid alcohol. Kinyoun stain is similar but does not require heating. (b) FLUOROCHROME STAIN with phenol-auramine or auramine-rhodamine; modified acid alcohol step and potassium permanganate counterstaining. Fluorescent mycobacteria are visible with 20 or 40x magnification. (2) CULTURE is the GOLD STANDARD. (a) Solid media can detect 10-100 organisms, takes 3-8 wks. Lowenstein Jensen is egg-based. Middlebrook 7H11 is agar based. Can detect colony morphology & mixed infections. (b) Liquid broth takes 1-3 wks to detect organisms. Middlebrook 7H12 and BACTEC systems. **CULTURE IS NECESSARY TO DETERMINE DRUG SUSCEPTIBILITIES**
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(MIDII #19)
MYCOBACTERIUM TUBERCULOSIS: Diagnostic Procedures => SPUTUM molecular diagnostics: (1)Nucleic Acid Amplification and (2) DNA Fingerprinting |
(1)Nucleic Acid Amplification can detect M. tuberculosis in fresh sputum. (Developed world technology, too costly for resource poor countries). Sensitivity is intermediate between acid fast smear and culture. If the AFB smear is negative, nucleic acid amplification is 40-77% sensitive. If the AFB smear is positive, nucleic acid amplification is 95% sensitive and nearly 100% specific. (2) DNA Fingerprinting: RFLP is also developed world technology. A restriction endonuclease produces DNA fragments; we separate the fragments by electrophoresis; apply a probe to a repetitive DNA sequence (insertion sequence 6110). There are numerous copies of IS6110 present in the M. tuberculosis chromosome at highly variable locations. Useful for: (a) identifying transmission from person-to-person; (b) distinguishing endogenous reactivation from exogenous reinfection in recurrent TB; (c) lab cross-contamination
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(MIDII #20)
MYCOBACTERIUM TUBERCULOSIS: Diagnostic Procedures => Chest X-Ray |
Luxury of developed world technology. CXR patterns of patients w/TB include: (1) Upper lobe infiltrate w/ or w/o cavitations (apical or sub-apical). This pattern is most common in reactivation disease in an intact immune system. The radiologic extent of disease reflects tissue damage, which reflects the host's ability to have a hypersensitivity rxn. (2) Hilar adenopathy w/or w/o infiltrates. Pattern is most common in AIDS patients, reflects minimal cellular immune response. (3) Pleural effusion: ALWAYS exudative. (a) Seen in post-primary infection, w/ scant organisms (this is a tissue hypersensitivity rxn). The smear will NEVER be positive. Culture is positive in 25% of cases. (b) Can also be seen as a complication of reactivation pulmonary TB, in which case organisms are more likely. Smear positive 50%; culture positive 60%. (4) Miliary pattern: (millet seed pattern). CXR shows 0.5-1.0 mm nodules. Follows childhood infection and disseminated infection. Also occurs in immunocompromised patients suffering from alcoholism, cirrhosis, & rheumatologic diseases, or patients being treated w/immunosuppressive agents. Dx can be tough – might be multiple organ involvement w/millet seed granulomas in tissues. Transbronchial biopsy is the highest yield diagnostic location. (5) Can also see atypical infiltrates.
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(MIDII #21)
MYCOBACTERIUM TUBERCULOSIS: General Principles of Treatment of TB |
Always use at least 2 drugs; usually begin with 3 or 4 pending sensitivities. There is a natural incidence of spontaneous drug resistance (1 in 10^5 organisms are resistant to each drug). Bacilli resistant to 1 drug will be killed with the other drug. Natural resistance to 2 drugs occurs spontaneously in 1 in 10^10 or 10^11. A prolonged treatment of 6-9 months is necessary if the organism is pan-sensitive. Directly observed therapy is advised for all patients. No one is 100% compliant regardless of age, sex, race, or education. Given daily treatment for the first 2 months; intermittent w/adjusted doses for continuation phase of 4-7 months depending on the regimen.
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(MIDII #22)
MYCOBACTERIUM TUBERCULOSIS: Discuss Drug Therapies |
ALL GIVEN ONCE DAILY TOGETHER: NEVER DIVIDE DOSES. (1) ISONIAZID (INH): bactericidal against dividing organisms. Causes hepatitis. Chemical = 20%, Clinical (age-related: <35=0.3%; >65=4%). (2) RIFAMPIN (RMP): bactericidal. Enables short course treatment (6-9 months vs. 18-24 months with non-RMP regimens). Causes drug-drug interactions. RMP is a potent INDUCER of hepatic microsomal enzymes (cytochrome P450). (3) PYRAZINAMIDE (PZA): enables shortening of the regimen from 9 months to 6 months. (4) ETHAMBUTOL (EMB): used in drug resistance and in situations where INH or RMP cannot be used (INH: hepatotoxicity; RMP: drug-drug interactions).
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(MIDII #23)
MYCOBACTERIUM TUBERCULOSIS: Who needs a PPD test? What is a positive PPD test? What is “the Booster phenomenon”? When do you treat a patient with a positive PPD? |
(I) Targeted testing: PPD is NOT a general screen. Only use PPD for patients at high risk of developing active TB: (1) Immunocompromised: HIV infected, chemotherapy patients, patients undergoing organ transplant, patients on immunosuppressive Rx for autoimmune diseases, rheumatoid arthritis. (2) Close contacts of infectious case (household or close working quarters). (3) Previously untreated patients with chest x-ray evidence of old fibrotic changes (not just calcified granuloma). (4) Recent immigrants (in US <5 yrs) from endemic areas. (5) Ppl who work in institutions where TB exposure is likely: hospitals, nursing homes, homeless shelters, prisons. (II) Definition of a positive PPD (purified protein derivative): 5 mm => HIV infected, close contacts of infectious case, chest x-ray evidence of old disease (fibrotic scarring, not just calcified granuloma); 10 mm => patients from endemic areas of TB. (III) The Booster Phenomenon: 2 step testing is essential for all those >55 whose exposure/infection was in the distant past and for those with BCG (the vaccine). (IV) Treat only those at high risk of reactivation, with INH for 9 months.
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(MIDII #24)
MYCOBACTERIUM TUBERCULOSIS: How do you determine of a positive PPD reactivity represents TB infection, not BCG? |
Enzyme-linked immunospot (ELISPOT) is a T-cell based assay from the blood. M. tuberculosis genes not present in M. bovis BCG produce an antigen to which T cells react. 1 tube of blood is needed for the test, which is not feasible in resource poor settings. This is useful in outbreaks for contact investigations.
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(MIDII #25)
MYCOBACTERIUM TUBERCULOSIS: Prevention => BCG Vaccine |
(1)What is it? This is an M. Bovis strain attenuated through serial passage. There is no standardized strain or procedure to make one.
(2) Does it work? The largest study performed in India suggests that there is no protection from TB infection. Other studies, done in England, suggest there is protection from TB infection. Prevalence of non-TB mycobacteria in a given region may interfere. The background prevalence of TB determines the utility of the vaccine. (3) Who uses it? All agree that it is highly effective for infants and small children in preventing dissemination and meningitis when infected by M. tuberculosis. Newborns are/should be vaccinated in all high prevalence areas of the world. |
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(MIDII #26)
FUNGI: While fungal virulence is not common, fungi are not casual pathogens. Most humans have a strong natural immunity to the fungi, but when this immunity is breached the consequences can be severe and dramatic. As modern medicine becomes increasingly adept at prolonging survival of patients with naturally-occurring immunocompromise (diabetes, cancer, AIDS), and causing iatrogenic immunocompromise in others (antibiotics, cytotoxic and immunomodulating drugs), fungal infections are becoming increasingly important, medically. |
Key take home point on fungi: **EVERY FUNGAL INFECTION IS “OPPORTUNISTIC”** Fungi are taking advantage in some way, eluding the patient's ordinarily competent defenses against them. The ways in which they do this vary.
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(MIDII #27)
Definition: FUNGUS |
A non-motile eukaryotic protist characterized by the absence of chlorophyll and the presence of a rigid cell wall.
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(MIDII #28)
Definition: YEAST |
A fungus growing as a round or oval unicellular organism, reproduced by budding or fission.
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(MIDII #29)
Definition: MOLD |
A fungus growing in hyphal form, reproduced by sexual or asexual spore formation.
[According to Wikipedia, a hypha (plural hyphae) is a long, branching filament. A typical hypha consists of a tubular wall, usually made of chitin, which surrounds, supports, and protects the cells that compose a hypha. For most fungi, a cell within a hyphal filament is separated from other cells by internal cross-walls called septa (singular septum).] |
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(MIDII #30)
Definition: HYPHA (pl. hyphae) |
A branching, tubular filament.
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(MIDII #31)
Definition: MYCELIUM (pl. mycelia) |
A mass of hyphae.
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(MIDII #32)
Definition: PSEUDOHYPHA (PSUEDOMYCELIUM) |
A filament (or mass of filaments) composed of many elongated yeast cells adherent to each other end to end.
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(MIDII #33)
Definition: DIMORPHIC |
Having the ability to transform between yeast and mold stages in response to specific changes in the environment.
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(MIDII #34)
Definition: SPORE |
The sexual or asexual reproductive unit of a mycelium
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(MIDII #35)
Definition: MYCOSIS (pl. mycoses) |
A human disease caused by a fungus. The term mycosis refers to conditions in which fungi pass the resistance barriers of the human body and establish infections. Mycoses are classified according to the tissue levels initially colonized: (1) Superficial mycoses are limited to the outermost layers of skin & hair; (2) Cutaneous mycoses extend deeper into the epidermis, as well as invasive hair & nail diseases. Host immune responses may be evoked, resulting in pathologic changes expressed in the deeper layers of skin. Dermatophytes cause these diseases, called ringworm (tinea). Cutaneous mycoses are caused by Microsporum, Trichophyton, and Epidermophyton fungi which comprise 41 species. (3) Subcutaneous mycoses involve the dermis, subcutaneous tissues, muscle, & fascia. Chronic, can be initiated by piercing trauma to the skin which allows the fungi to enter. Difficult to treat, may require surgical debridement. (4) Systemic mycoses due to primary pathogens originate primarily in the lungs and may spread to many organ systems. Organisms are inherently virulent, generally dimorphic. (5) Systemic mycoses due to opportunistic pathogens: infections of patients with immune deficiencies who would otherwise not be infected. Examples of immunocompromised conditions include AIDS, alteration of normal flora by antibiotics, immunosuppressive therapy, and metastatic cancer. Examples of opportunistic mycoses include Candidiasis, Cryptococcosis, and Aspergillosis.
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(MIDII #36)
Distinctions between Bacteria & Fungi (1)Size; (2) Nuclear Structure; (3) Cell Membrane Composition; (4) Cell Wall Composition; (5) Respiration; (6) Metabolism; (7) Preferred Temperature; (8) Toxin Production; (9) Laboratory Stain of Choice; (10) Important Immunity |
(1) SIZE: (F) diameter 2-10 microns, volume (yeasts) 20-50 microns; (B) diameter 1 micron, volume 1-5 microns. (2) NUCLEAR STRUCTURE: (F) eukaryotic; (B) prokaryotic. (3) CELL MEMBRANE COMPOSITION: (F) sterols present (ergosterol); (B) no sterols present. (4) CELL WALL COMPOSITION: (F) chitin, glucans, mannans; (B) peptidoglycans, lipopolysaccharides, lipoproteins. (5) RESPIRATION: (F) aerobes or facultative anaerobes. No strict anaerobes; (B) aerobic or anaerobic. (6) METABOLISM: (F) heterotrophic; (B) heterotrophic or autotrophic. (7) PREFERRED TEMPERATURE: (F) usually 25-35 deg C; (B) usually 37 deg C. (8) TOXIN PRODUCTION: (F) rarely; always irrelevant in human infection; (B) occasionally; may be impt in human infection. (9) LAB STAIN OF CHOICE: (F) KOH preparation of smears, methenamine silver or PAS stains of tissue. Gram stain is unreliable; (B) Gram stain. (10) IMPT IMMUNITY: (F) cellular immunity is most important, with the role of Abs still under investigation; (B) humoral and cellular immunity are both important.
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(MIDII #37)
Discuss Clinical Categories of Fungal Infections: |
(1)Superficial/Cutaneous: infection of the outer layer of skin by lipophilic or keratinolytic fungi (e.g. Pityriasis, Dermatophytosis); (2) Subcutaneous: infection of subcutaneous tissues from the traumatic implantation of the fungus into the skin (e.g. Sporotrichosis); (3) “The True Pathogenic Fungi” can cause disease even in immunocompetent hosts (e.g. Histoplasmosis, Coccidioidomycosis, Blastomycosis); (4) “The Opportunistic Fungi” generally cause disease only in immunocompromised hosts (e.g. Cryptococcus, Candidiasis, Aspergillosis, Mucormycosis)
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(MIDII #38)
Distinguish between pathogenic and opportunistic fungi with regard to the following categories: (1) Habitat; (2) Morphology; (3) Route of Infection; (4) Host Infected; (5) Host Response; (6) Immunity; (7) Prognosis |
(1)HABITAT: (Pathogens) Generally confined to endemic areas; (Opportunists) Omnipresent; (2) MORPHOLOGY: (P) Dimorphic; (O) No true dimorphs; (3) ROUTE OF INFECTION: Usually pulmonary; (O) varies; (4) HOST INFECTED: (P) Often 'normal'; (O) Usually immunocompromised; (5) Host Response: (P) Pyogenic or granulomatous; (O) Necrosis to pyogenic to granulomatous, depending on degree of host impairment; (6) IMMUNITY: (P) Resolution imparts strong specific immunity; (O) No specific resistance to reinfection; (7) PROGNOSIS: (P) Most resolve spontaneously; (O) Depends on degree of host impairment.
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(MIDII #39)
Name the primary host defense against the following fungi: (1) Dermatophytes, (2) Sporothrix, (3) Histoplasma, (4) Blastomyces, (5) Coccidioides, (6) Cryptococcus, (7) Candida, (8) Aspergillus, (9) Mucorales |
(1) Dermatophytes: intact skin barrier; (2) Sporothrix: intact skin barrier; (3) Histoplasma: lymphocyte function; (4) Blastomyces: lymphocyte function; (5) Coccidioides: lymphocyte function; (6) Cryptococcus: lymphocyte function, possibly humoral immunity; (7) Candida: cutaneous infection => intact skin barrier; mucocutaneous infection => lymphocyte function; disseminated infection: PMN function, intact skin and mucosal barrier; (8) Aspergillus: invasive infection => PMN function; (9) Mucorales: invasive infection => PMN function
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(MIDII #40)
Superficial Fungal Infections: DERMATOPHYTOSIS |
(ORGANISM): Caused by Dermatophytes (members of the general Trichophyton, Microsporum, Epidermophyton). (MYCOLOGY): Related species of mold all possessing keratinases. (EPIDEMIOLOGY): Omnipresent. (PATHOGENESIS): Spores on shed skin or hairs adhere to the stratum corneum, germinate, and invade. Individual susceptibility varies. Organisms are confined to the stratum corneum, with surrounding inflammation penetrating deeper layers of skin. (CLINICAL): Tinea corporis (ringworm), Tinia pedis (athlete's foot), Tinea cruris (jock itch), Tinea capitis (scalp and hair), onychomycosis (nails). (DIAGNOSIS): characteristic appearance, KOH preps or Wood's light exam, smear and culture of specimen. (TREATMENT): topical (azoles), systemic (griseofulvin, azoles, allylamines)
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(MIDII #41)
Superficial Fungal Infections: PITYRIASIS VERSICOLOR |
(ORGANISM): Malassezia furfur. (MYCOLOGY): A lipophilic yeast, part of the normal skin flora. (EPIDEMIOLOGY): Omnipresent; the disease is more prevalent in the tropics. (PATHOGENESIS): Yeasts proliferate in settings of lipids and sweat. Rare in kids, appears in adolescence. (CLINICAL): Pityriasis = tinea versicolor. Seborrheic dermatitis. Infusion of lipid-containing nutritional solutions is rarely associated with M. furfur bacteremia. (DIAGNOSIS): Characteristic appearance; UV light fluorescence. (TREATMENT): Topical (selenium sulfide or azoles), catheter removal for fungemia
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(MIDII #42)
Subcutaneous Fungal Infections: SPOROTRICHOSIS |
(ORGANISM): Sporothrix schencki. (MYCOLOGY): Dimorphic. Grows as mycelium in culture; as yeast w/variably sized and shaped cells in the host. (EPIDEMIOLOGY): Worldwide distribution in soil, especially Mexico and South America. (PATHOGENESIS): Thorny plants (roses) or splinters inoculate fungus into subcutaneous tissues. Infection spreads slowly along draining lymphatics. Tissue reaction is mixed pyogenic and granulomatous. Fungi are often difficult to identify in lesions. (CLINICAL): Small hard nodule at the primary inoculation site discolors and ulcerates. There are multiple similar nodules along lymphatics, which themselves become hard and cordlike. Rare bone and joint involvement; rarer dissemination. Likelihood of severe disease appears to be increased with poor nutrition or repeated exposure. (DIAGNOSIS): Culture of tissue or drainage (fungi are rarely seen on smear or section). Skin test determines exposure but not disease. (TREATMENT): ketoconazole, itraconazole, amphotericin B.
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(MIDII #43)
The “Pathogenic” Fungi: HISTOPLASMOSIS Organism, Mycology, Epidemiology, Pathogenesis |
(ORGANISM): Histoplasma capsulatum. (MYCOLOGY): Dimorphic fungus: grows as mycelium in culture; as small budding yeasts in host. (EPIDEMIOLOGY): Worldwide distribution in soils w/high nitrogen content – guano of birds, poultry, bats. Caves. Starling habitats. Endemic in the Ohio-Mississippi Valley, Central & South America, Puerto Rico. (PATHOGENESIS): Spores are inhaled from the soil, transform to yeast in the lungs, where they are phagocytosed by MΦs with intracellular multiplication, dissemination, granulomatous host response as in TB. May resolve with scarring, remain active in the lungs, or disseminate in settings of immunocompromise. Moves through reticuloendothelial organs (liver, spleen, lymph nodes). Like TB, may reactivate years after the initial exposure (in the context of AIDS, etc.)
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(MIDII #44)
The “Pathogenic” Fungi: HISTOPLASMOSIS (II) Clinical presentation, Diagnosis, Treatment |
(CLINICAL) 1) Self-limited disease => asymptomatic (95%) or flu-like syndrome. Noninfectious complications of healing may include mediastinal fibrosis or pericarditis. 2) Chronic pulmonary disease mimics TB; most common in settings of prior lung damage. 3) Disseminated disease (0.01%): fever, wasting, variable hepatosplenomegaly, ulcerations in mouth, GI tract, adrenal insufficiency, pancytopenia. (DIAGNOSTIC TESTS): Skin test confirms exposure, but not infection. It may artificially boost subsequent serologic testing. Antibody titers are often unreliable, especially in settings of immunocompromise. Antigen detection in serum and urine is sensitive but not commercially available. (DIAGNOSIS) 1) Pulmonary: exposure + compatible illness + compatible x-ray + Ab titer +/- sputum culture. 2) Disseminated disease: organisms seen intracellularly in blood/bone marrow/liver/urine/tissue and/or grown in culture. (TREATMENT) Mild pulmonary: none. Severe pulmonary or disseminated: Amphotericin B
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(MIDII #45)
The “Pathogenic” Fungi: COCCIDIOIDOMYCOSIS (“Cocci”) |
(ORGANISM): Coccidioides immitis; (MYCOLOGY): Dimorphic => grows as mycelium in culture; as spherules producing endospores in host; (EPIDEMIOLOGY): Endemic in arid, hot areas of North, Central, South America ('the lower Sonoran life zone.') Creosote bushes and rodent burrows. Soil organisms aerosolize late summer-fall. Note outbreak of cocci in Southern California immediately following LA earthquake of fall 1994. (PATHOGENESIS): Inhaled spores swell into spherules in the lung, burst releasing hundreds of endospores. Spherules evoke mononuclear response, endospores are neutrophilic. Pulmonary pathology: consolidation, caseation, necrosis, cavity, and nodule formation. Hematogenous dissemination of endospores to meninges, skin, bone, liver, spleen with lesions ranging from pyogenic abscesses to granulomas. Reactivation years after exposure may occur.
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(MIDII #46)
The “Pathogenic” Fungi: COCCIDIOIDOMYCOSIS (“Cocci”) |
(CLINICAL): 60% asymptomatic or mild pulmonary infection. 40% significant pulmonary infection: fever, cough, malaise, sputum production, erythema multiforme (“Valley Fever”). 5% progressive pulmonary disease, residual pulmonary nodule or cavity. 0.5% disseminated disease (more common in men, pregnancy, dark-skinned races, immunocompromise). Skin: fungating masses or ulcers; bone: osteolytic and/or blastic lesions; meninges (25%): chronic meningitis.(DIAGNOSIS): Coccidioidin skin test positive 1-3 wks after infection but not reliable: anergy common in disseminated disease. Complement fixation antibody may be (+) in disseminated disease, but not helpful in immunocompromised hosts. Best: smear and culture of pus, tissue. (TREATMENT): For severe primary disease, for primary disease in persons at risk of dissemination, for disseminated disease. Amphotericin B; fluconazole; itraconazole
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(MIDII #47)
The “Pathogenic” Fungi: BLASTOMYCOSIS |
(ORGANISM): Blastomyces dermatitidis. (MYCOLOGY): Dimorphic fungus. Grows as mycelium in culture, as large yeasts with refractile cell walls and broad-based buds in host. (EPIDEMIOLOGY): Primarily in humid, wooded areas of North America. Prefers decaying organic matter and wood to soil. Outbreaks associated with log cabin building, peanut harvesting, camping, beaver dam viewing. (PATHOGENESIS): Conidia inhaled, convert to yeast form in lungs. Evoke neutrophilic and granulomatous response. Dissemination via infected MΦs to skin, bone, urinary tract. In skin, pseudoepitheliomatous hyperplasia can simulate squamous cell cancer. (CLINICAL): Frequency of asymptomatic infection unknown. Pulmonary infection mimics histoplasma, TB. Disseminated disease: Skin involvement is most common: ulcerating, heaped-up pigmented nodules face/hand/legs/mucosa +/- sinus tracts. 25-50% bone disease: well-demarcated osteolysis long bones/skull. Urogenital disease 5-20%: epididymitis/prostatitis/scrotal ulcers. Disease of liver, spleen, GI tract rare. (DIAGNOSIS): No adequate skin test, Ab or Ag assays exist. Best option is smear or culture of affected site. (TREATMENT): Amphotericin B, ketoconazole, itraconazole
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(MIDII #48)
The “Opportunistic” Fungi: CRYPTOCOCCOSIS |
(FUNGUS): Cryptococcus neoformans. (MYCOLOGY): A yeast without a clinically relevant mold phase. Characterized by unique thick polysaccharide capsule. (EPIDEMIOLOGY): The pigeon and its excreta, worldwide. Some species colonize eucalyptus trees instead. (PATHOGENESIS): Aerosolized yeasts inhaled. Pulmonary disease (nodular, miliary) may occur. Hematogenous dissemination to CNS, where symptomatic human disease most common. Result: edematous, mucoid, cloudy meninges, usually with a poor inflammatory response. Intracerebral masses of yeasts may form (cryptococcomas). (CLINICAL): Acute or chronic meningitis, w/headache, fever, elevated intracerebral pressure. Often associated w/AIDS or other immunocompromise, although cases in apparently normal hosts do occur. Cell-mediated immunity of paramount importance. Ab is formed against capsule and may play a role in host defense. (DIAGNOSIS): India ink preparation, culture of CSF (or other body site). Polysaccharide capsule allows for easy cryptococcal Ag assay in serum or CSF -> sensitive and specific when titers are high. (TREATMENT): Amphotericin B +/- 5-flucytosine; fluconazole.
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(MIDII #49)
The “Opportunistic” Fungi: CANDIDIASIS |
ORGANISM: Candida albicans; MYCOLOGY: Yeast cells, pseudohyphae & hyphae in both culture & host. Organism stains Gram (+); EPIDEMIOLOGY: Normal inhabitant of the alimentary tract & mucosa (mouth, vagina, anus). NOT on normal skin, although damage, moisture, or any biochemical change leads to rapid colonization. Also predisposing to colonization: infancy, debilitation, pregnancy, antibiotics.
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Discuss the PATHOGENESIS of CANDIDIASIS!!
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(PATHOGENESIS): Primary host defenses consist of intact skin and mucosa w/normal pH & flora (oral, GI tract, vaginal). Antibiotics, pregnancy, skin maceration leaves even healthy ppl susceptible to superficial Candida infection. Dissemination occurs via defect in mucosa, or formation of biofilm on a catheter/foreign body. Once organism gets thru dermis or into blood, PMNs are 1st line of defense: phagocytize & kill blastopores, damage psuedohyphae. Monocytes & Eos can ingest & kill the organism. Phagocytes w/o myeloperoxidase, or w/o ability to generate superoxide ion can't kill effectively. Serum or plasma alone (with Abs & complement) CANNOT kill Candida. Complement IS necessary for opsonization; IgG also opsonizes. Patients w/disseminated Candidiasis can have a significant Ab response to infection. Lymphocytes protect against proliferation on the skin or mucosa, so HIV infection predisposes primarily to oral/vaginal candidiasis. NK cells w/ anti-candidal activity have been ID'd. Lymphocyte cytokines are necessary to recruit phagocytes in disseminated disease.
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(MIDII #50)
The “Opportunistic” Fungi: CANDIDIASIS Discuss Virulence Factors of Candida albicans!! |
There are NO hypervirulent species of candida. People are infected by their own previously nonpathogenic flora, NOT someone else's “monster strain.” Virulence factors include: (a) ENVIRONMENTAL TOLERANCE => survive acid pH (stomach), bloodstream, mucosal surfaces. (b) SECRETED HYDROLASES => produce extracellular proteases, phospholipases, and other enzymes that destroy CT and kill host cells. (c)ADHERENCE => to host cells as well as dentures, catheters, and prosthetic devices. (d) Ability to grow in HYPHAL form => induced by presence of serum and long associated w/invasive disease in tissue sections. Hyphal form protects yeast after phagocytosis, allowing escape from the phagocytic cell and progression of infection. In the mouse model, mutant Candida deficient in hyphal formation was avirulent. NOTE: gene INT1 encodes surface protein Int1p which enables the organism to grow esp in filamentous form and seems linked to virulence. In vitro, superantigen-like effects (T cells activated; cascade of cytokines ---> sepsis syndrome) result when Int1p is cleaved by heparin (a common clinical anticoagulant).
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(MIDII #51)
The “Opportunistic” Fungi: CANDIDIASIS Discuss the Clinical Presentation of Infection w/Candida albicans, Diagnosis & Treatment |
Mucocutaneous: thrush (oral candidiasis); vaginitis, balanitis, onychomycosis; esophageal candidiasis. UT: dysuria, fever. Disseminated: fever, chills, renal dysfunction, endophthalmitis, skin lesions. Cellular immunity is most impt in protecting against mucosal infection. PMNs protect against invasion.
Dx: (1) Pathognomonic appearance (thrush); (2) Smear/culture of usually sterile site (distinction between colonization and infection can be tricky); (3) Pathologic confirmation: organism in tissue. Rx: (1) Remove the breach of host defense! (2) Local (nystatin, clotrimazole); systemic (amphotericin B, fluconazole, voriconazole, caspofungin) |
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(MIDII #52)
The “Opportunistic” Fungi: ASPERGILLOSIS |
(Organism): Aspergillus fumigatus, A. flavus, others. (Mycology): A mold w/o a yeast phase. Hyphae are septate & dichotomously branch @ acute angles, like extended fingers. Fruiting heads seen in vitro. (Epidemiology): Ubiquitous in the environment. Air, compost, soil, debris. Isolated from snow in the antarctic, winds over the Sahara, an English apple orchard in the spring. Also found on birds and chickens.
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(MIDII #52)
The “Opportunistic” Fungi: ASPERGILLOSIS (Organism): Aspergillus fumigatus, A. flavus, others. (Mycology): A mold w/o a yeast phase. Hyphae are septate & dichotomously branch @ acute angles, like extended fingers. Fruiting heads seen in vitro. (Epidemiology): Ubiquitous in the environment. Air, compost, soil, debris. Isolated from snow in the antarctic, winds over the Sahara, an English apple orchard in the spring. Also found on birds and chickens. Discuss the PATHOGENESIS, CLINICAL PRESENTATION, DIAGNOSIS (Dx), and TREATMENT (Rx) of infection with Aspergillus fumigatus or Aspergillus flavus. |
(A: Pathogenesis) => Airborne spores are inhaled. May lead to: (1) Hypersensitivity in airways (allergic bronchopulmonary aspergillosis). (2) Massive local growth in preexisting abnormality in lungs (aspergilloma). (3) Invasive disease in settings of neutropenia, steroid use: organism penetrates lung parenchyma & vasculature, causing dense pulmonary consolidation, necrosis, cavitation. May occur in sinuses as well. Hematogenous dissemination to skin, bone, heart. (B: Clinical) => (a) Allergic: wheezing, cough, dyspnea; (b) Aspergilloma: hemoptysis; © Invasive pulmonary: fever, dyspnea, systemic toxicity. Phagocytic defenses are of paramount importance (PMNs, monocytes, MФs), cell-mediated immunity is less impt. (C: Dx) => Stain & culture of biopsy specimen. (+) culture of a secretion may represent contamination. (D: Rx) => (a) Allergic: corticosteroids; (b) Aspergilloma: surgery; (c) Invasive: Amphotericin B; itraconazole; voriconazole; caspofungin.
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(MIDII #53)
The “Opportunistic” Fungi: MUCORMYCOSIS (phycomycosis, zygomycosis) (Organisms): Species of the order Mucorales, esp rhizopus. (Mycology): Molds w/o a yeast phase. Broad, nonseptate hyphae, haphazardly branching at right angles. Thrive in warm, acid, sugary solutions. (Epidemiology): Ubiquitous in decaying organic debris – e.g. Moldy bread. Discuss PATHOGENESIS, CLINICAL, DIAGNOSIS & TREATMENT of Infection with Mucorales family of fungi. |
(Pathogenesis): Spores are inhaled into the alveoli & the nasal turbinates. If unchecked, grow w/blood vessel invasion. Erode thru sinuses, nerves, bone. Thrombosis, infarction, tissue necrosis, surrounded by neutrophilic cellular infiltrate. (Clinical): Most fulminant fungal infection known! Disease almost uniformly confined to patients w/acidosis (diabetes, diarrhea, uremia, salicylate ingestion) or leukemia, occasionally other forms of immunocompromise. PMNs are the primary defense, so neutropenia is a major risk. Rare in AIDS but reported. (a) Rhinocerebral: facial pain, headache, sinusitis, facial swelling, orbital cellulitis, cranial nerve signs. (b) Pulmonary: cough, hemoptysis, rapidly progressive pulmonary insufficiency. (Dx): Stain and culture of biopsy specimen. (Rx): Correct hyperglycemia, acidosis, immunocompromise, Amphotericin B
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(MIDII #54)
Targets of Antifungal Agents: Discuss POLYENES (amphotericin B, nystatin) Amphotericin B is produced by Streptomyces nodosus (aerobic actinomycete). (MOA): Focuses on fungal cytoplasmic membrane and binding to sterols, specifically ergosterol. Amphotericin B increases cell membrane permeability via pore and channel formation resulting in fungal cell death from loss of intracellular molecules. (Resistance): Resistance to amphotericin is rare. Resistant strains show slower growth rates and less virulence in vitro. 2 possible mechanisms: (a) resistant mutants replace ergosterol w/other precursor sterols; (b) failure of amphotericin to penetrate the fungal cell wall. Discuss SPECTRUM and PHARMACOKINETICS of Amphotericin! |
(Spectrum): Amphotericin is the most broad spectrum antifungal and is considered the GOLD STANDARD for Rx of a variety of fungal infections including Candida, Cryptococcus neoformans, Blastomyces dermatitidis, Histoplasma capsulatum, Sporothrix schenkii, coccidiodomycosis, paracoccidiodes, Aspergillus, Penicillium, mucormycosis. (Pharmacokinetics): Available only as an injection for IV use. Oral suspension may be compounded for RX of oropharygeal & esophageal candidal infections. When given orally it has negligible GI absorption and is not reliable for treatment of systemic infections. After IV administration, most drug leaves circulation quickly. Stored in liver and other organs. Reenters circulation slowly. Extensively bound to tissues. Half-life is prolonged (~15 days) and can be detected in the body up to 7 wks after discontinuing therapy. 2-5% of each dose is excreted unchanged in the urine. Most drug is degraded in the body. No dose adjustment is needed in patients w/renal and/or hepatic dysfunction. Amphotericin achieves its highest concentrations in the liver & spleen w/less in the kidneys & lungs. It doesn't appear to penetrate CSF, brain, pancreas, muscles, bone, vitreous humor, normal amniotic fluid, & bronchial secretions well.
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(MIDII #55)
Targets of Antifungal Agents: Discuss POLYENES (amphotericin B, nystatin) Discuss FORMULATIONS of Amphotericin! |
Amphotericin B deoxycholate: amphotericin is insoluble in water & is formulated as a complex w/the bile salt deoxycholate. This is “conventional” amphotericin B. Lipid formulation of amphotericin are advantageous w/respect to toxicities. Nephrotoxic but cause less nephrotoxicity than conventional amphotericin. 30-50 times more expensive so their use is cost limited. No difference in efficacy. (a) Amphotericin B colloidal dispersion (ABCD, Amphotec) is a colloidal dispersion containing equal amts of amphotericin B and cholesteryl sulfate. ABCD particles are disk shaped. (b) Amphotericin B lipid complex (ABLC, Abelcet) contains dimyristoyl phophatidylcholine and dimyristoyl phosphatidylglycert in a 7:3 mixture w/35 mol % amphotericin in a ribbon-like sheet structure. © Liposomal amphotericin B (Ambisome) is a unilamellar liposome (one molecule ampho B per 9 molecules lipid). Lipid contains phosphatidylcholine, cholesterol, and distearoylphosphatidylglycerol in a 10:5:4 molar ratio.
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(MIDII #56)
Targets of Antifungal Agents: Discuss POLYENES (amphotericin B, nystatin) Discuss TOXICITIES of Amphotericin: NEPHROTOXICITY |
(1)Nephrotoxicity => All amphotericin products cause some degree of nephrotoxicity. Manifests as a dose-dependent decrease in glomerular filtration rate (GFR) via direct vasoconstrictive effect on afferent renal arterioles. Also: potassium, magnesium, and bicarbonate wasting, and decrease in erythropoietin production. Permanent renal failure is related to the total dose and is due to destruction of renal tubular cells, disruption of the tubular basement membrane, and loss of functioning nephron units. Risk factors for nephrotoxicity include concomitant nephrotoxic drugs (cyclosporine, aminoglycosides), hypotension, intravascular volume depletion, renal transplant, and other pre-existing renal conditions. Nephrotoxicity may be reduced by saline loading w/each dose. May not be possible if patients can't tolerate fluids (heart failure, renal failure, other fluid overload states). Lipid products are less nephrotoxic, but can still cause nephrotoxicity.
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(MIDII #57)
Discuss TOXICITIES of Amphotericin: (2) Electrolyte Abnormalities & (3) Infusion Related Reactions |
(2) Electrolyte Abnormalities => Renal tubular acidosis and renal wasting of potassium, magnesium, and phosphate is seen during treatment w/ amphotericin and for several wks after treatment is discontinued. Close monitoring (daily) and electrolyte supplementation are necessary. (3) Infusion Related Rxns (IRRs) => Common early in course. Rxns are most severe w/1st 3-5 doses. Usually subside w/cont'd use & premedications. Chills, fever, tachypnea may occur during infusion. Premedicating w/diphenhydramine & acetominophen for all doses can diminish rxns. Is recommended. If severe shaking chills (rigors) occur, infusion are temporarily discontinued and meperidine administered to shorten the rigor. These rxns are expected. Should NOT be mistaken for anaphylaxis. Allergic rxns can occur but are extremely rare. (4) Other Rxns => Nausea and vomiting are common. Thrombophlebitis may occur w/peripheral administration. A normocytic, normochromic anemia may occur and is associated w/decreased epoetin levels.
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(MIDII #58)
Discuss CLINICAL USES of Amphotericin |
(1)Candidiasis (azole resistant strains, too), Cryptococcal meningitis, mucormycosis, invasive aspergillosis; (2) Empiric therapy in patients with febrile neutropenia; (3) Intrathecally for coccidiodal meningitis; (4) Intraocular injections for fungal endopthlamitis; (5) Bladder irrigation for fungal cystitis; (6) Oral suspension for oropharyngeal and esophageal candidiasis.
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(MIDII #59)
FLUCYTOSINE => Flucytosine is a fluorinated pyrimidine related to fluorouracil. It is deaminated to 5-fluorocytosine. (MOA): Flucytosine is deaminated to 5-FC, then converted to 5-fluorodeoxyuridylic acid monophosphate which is a noncompetitive inhibitor of thymidylate synthetase and interferes with DNA synthesis. Mammalian cells do not convert flucytosine to fluorouracil, so flucytosine is selective for fungi. (Mechanisms of Resistance): Drug resistance arises during therapy, especially monotherapy. The mechanism can be loss of the permease necessary for cytosine transport or decreased activity of UMP pyrophosphorylase or cytosine deaminase. Discuss: SPECTRUM, PHARMACOKINETICS, TOXICITIES, and CLINICAL USES |
(Sp): Flucytosine has useful activity (in combo w/other agents) against Cryptococcus neoformans, Candida, & chromomycoses. (Ph): Available for oral admin only. Rapid, complete absorption from GI tract. Excreted RENALLY w/90% excreted unchanged in urine. Req's dose adjustment in pts w/renal disease. Penetrates well into CSF (75% of serum levels), aqueous humor, joints, bronchial secretions, peritoneal fluid, brain, bile, & bone. Usual half-life is ~3-6 hrs, but may be increased to ~200 hrs in pts w/renal failure. Serum [Cx] monitoring is recommended. (Tox's): (1) Bone marrow suppression = most common & severe toxicity. Dose-related; associated w/concentrations >100-125mcg/mL. Leukopenia & thrombocytopenia are usual manifestations. Risk factors: underlying hematologic disorders & concomitant BM suppressive drugs. (2) Nausea, vomiting, diarrhea (GI disturbances) are also common. (Clin): Clinically useful against cryptococcal, candidal, & chromomycoses, but NOT a drug of choice. Not as efficacious as other agents. Associated w/development of resistance. Usually used in combo w/other agents (commonly amphotericin).
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(MIDII #60)
Discuss AZOLES as a class of antifungal agents. |
(MIDII #60)
Discuss AZOLES as a class of antifungal agents. |
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(MIDII #61)
Discuss KETOCONAZOLE, an AZOLE Ketoconazole is a synthetic imidazole antifungal. Rarely used. (Spectrum): Used to treat mucocutaneous candidiasis, coccidiodomycosis, histoplasmosis, paracoccidiodomycosis, and blastomycosis in nonimmunosuppressed patients. Not effective for aspergillosis or mucormycosis. (Pharm): Only available for oral administration, absorption varies between individuals. Acidic environment req'd for absorption (affected by antacids and H2-histamine antagonists). Ketoconazole is LIVER metabolized, excreted as inactive drug in BILE, to a small extent in urine. T ½ = 8 hrs. Moderate liver dysfunction has no effect on ketoconazole blood levels. Inhibits CYP3A4. Ketoconazole levels in CSF are minimal (<1%) compared to plasma. Discuss Ketoconazole's TOXICITIES and CLINICAL USES: |
(TOXICITIES): GI disturbances include dose-dependent nausea, vomiting, and anorexia. Endocrinopathies: Ketoconazole inhibits steroid biosynthesis in humans (as it does in fungi) and may result in endocrinopathies. Causes a dose-dependent decrease in testosterone synthesis and can suppress androgen production. Gynecomastia and oligospermia in men and menstrual irregularities in women have been seen. Hepatotoxicity may occur but is less common. Majority of cases occur in the first 3 months of therapy. (CLINICAL USES): Ketoconazole use is very limited for fungal infections and has largely been replaced with itraconazole. Topical ketoconazole shampoo is the most commonly used formulation of ketoconazole.
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(MIDII #62)
Discuss ITRACONAZOLE, an AZOLE => Spectrum, Pharmacokinetics |
Itraconazole is a triazole antifungal w/broader spectrum of activity, a more desirable pharmacokinetic profile, & less toxicity than ketoconazole. Still limited by pharmacokinetics, drug interactions, & toxicities. (SPECTRUM): Blastomycosis, histoplasmosis, coccidiodomycosis, paracoccidiodomycosis, sporotrichosis, ringworm (including onychomycosis), tinea versicolor, & aspergillosis. (PHARMACOKINETICS): Until recently, itraconazole was only available in an oral formulation. Use of this agent has been limited due to variability in Cx's achieved following oral dosing and association w/treatment failures. It is water insoluble. Available in oral capsules and an oral soln. The soln is coformulated w/cyclodextrin to improve H2O solubility and absorption (30% greater than capsules). Oral absorption of capsules is improved w/food. Soln is best absorbed on an empty stomach. Tissue, pus, and bronchial secretion Cx's are higher than plasma levels. CSF and ocular levels are low. Primarily metabolized in the liver by CYP3A4 and also inhibits this enzyme system. Subject to drug interactions. T ½ = 30-40 hrs, will be prolonged in pts w/severe liver disease.
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(MIDII #63)
Discuss ITRACONAZOLE, an AZOLE => Toxicities and Clinical Uses |
(TOXICITIES): (a) GI disturbances: dose-related nausea, diarrhea, & abdominal discomfort. (b) Hepatotoxicity. (c) Thrombophlebitis => venous inflammation with thrombus formation. Significant thrombophlebitis is associated w/the IV formulation when it is administered peripherally. Increased fluid dilation volume is often necessary. (d) Negative inotrope: IV administration in dogs and humans has resulted in neg inotropic effects. Should not be administered to pts w/congestive heart failure or pts w/ventricular dysfunction for the treatment of onychomycosis. (CLINICAL USES): (a) Treatment of pulmonary & extrapulmonary blastomycosis. (b) Histoplasmosis, including chronic cavitary pulmonary disease & disseminated, nonmeningeal histoplasmosis. (c) Pulmonary & extrapulmonary aspergillosis, usually in pts who are resistant to treatment (refractory) with amphotericin or who are intolerant to amphotericin. (d) Empiric fungal therapy in pts w/neutropenic fever.
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(MIDII #64)
Discuss FLUCONAZOLE, an AZOLE => Spectrum and Pharmacokinetics |
Fluconazole is the best tolerated and most widely used antifungal agent. (Spectrum): Candidiasis, Cryptococcus neoformans, Coccidiodomycosis. SOME activity against sporotrichosis, ringworm, histoplasmosis, and blastomycosis, but NOT as efficacious as itraconazole. NO activity against Aspergillus or mucormycosis. (Pharmacokinetics): Available in both oral and IV forms. Oral formulation is very well absorbed from the GI tract. Bioavailability is >80%. Oral absorption is not affected by pH. Fluconazole is mainly excreted renally w/60-75% of the drug appearing unchanged in the urine. Dose adjustment is necessary in pts w/renal disease. Penetrates well into saliva, sputum, urine, and other body fluids including CSF (~70% of plasma levels) and brain. Subject to a limited number of drug interactions including interactions w/phenytoin, cyclosporine, warfarin, rifampin, rifabutin, sulfonylureas, and tacrolimus.
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(MIDII #65)
Discuss FLUCONAZOLE, an AZOLE => Toxicities & Clinical Uses |
(Toxicities): Adverse effects are uncommon. Nausea, vomiting, anorexia may occur at higher doses. Rare hepatotoxicity has occurred (with high, prolonged doses).
(Clinical Uses): Commonly used for infections caused by susceptible Candida sp. (systemic, cutaneous, oropharyngeal, esophageal, intra-abdominal, vaginal, etc.). Has been used as initial treatment and maintenance of cryptococcal meningitis in HIV patients. Fungal prophylaxis in neutropenic patients. Coccidiodomycosis (meningitis and disseminated). |
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(MIDII #66)
Discuss VORICONAZOLE, an AZOLE => Spectrum & Pharmacokinetics |
Voriconazole is the newest triazole antifungal. Structurally related to fluconazole. Expands on fluconazole's clinical activity to include fluconazole-resistant Candida sp., Aspergillus sp., and rare molds (Scedosporium sp., Fusarium sp.) Appears fungistatic against yeast but fungicidal against molds. Available orally w/good bioavailability. Attractive option for long term maintenance therapy for mold infections in immunosuppressed pts. Pharmacokinetic profile is significantly improved over itraconazole but drug interactions and toxicity may still be problematic.
(Spectrum): Candida sp. (incl. most fluconazole-resistant strains), Aspergillus sp., Blastomyces dermatitidis, Coccidiodes immitis, Histoplasma capsulatum. Some strains of Pseudoallescheria boydii, Scedosporium apiospermum, Fusarium sp., Paecilomyces sp., Bipolaris sp., & Alternaria sp. Voriconazole is less active against Sporothrix schenkii. (Pharmacokinetics): Available in IV & ORAL formulations. Oral is best absorbed on an empty stomach w/>90% bioavailability. Exhibits nonlinear pharmacokinetics in adults due to saturation of metabolism. Significant degree of interpatient variability in serum Cx's. In children, elimination is linear; higher doses are req'd to attain similar Cx's as adults. Large Vd & distributes well into CSF (50% of plasma Cx). Metabolized in the liver by CYP2C9, CYP3A4, CYP2C19. Drug interactions are of major importance in drug safety; should be carefully evaluated. Usual t ½ is 6 hrs. Dosage adjustment necessary in pts w/liver dysfunction. The IV form is formulated w/SBECD to increase solubility of voriconazole. SBECD is eliminated via kidneys & accumulates in pts w/renal disease. Use is NOT recommended in pts w/CrCL < 50 ml/min w/o risk/benefit evaluation. |
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(MIDII #67)
Discuss VORICONAZOLE, an AZOLE => Toxicities and Clinical Uses |
(Toxicities): (a) Visual Disturbances occur in 30% of pts but rarely results in discontinuation of therapy. Symptoms occur early in therapy w/1st few doses, begin within 30 min of a dose, and last for 30 min. Visual effects include altered color discrimination, blurred vision, appearance of bright spots, & photophobia. Associated w/changes in electroretinogram tracings, which normalize upon discontinuation of treatment. (b) Hepatotoxicity: elevations in hepatic enzyme levels may occur w/ voriconazole. Most patients have asymptomatic elevations, but life threatening hepatitis has been described. Dose-related effects. Resolve w/discontinuation of therapy. (c) Skin Rashes: Skin rxns have been associated w/voriconazole. Most have been characterized as a photosensitivity rxn. (Clinical Uses): (1) Primary or salvage therapy of invasive aspergillosis. (b) Infections due to fluconaole-resistant Candida sp. (c) Treatment of Psuedoallescheria/Scedosporium and Fusarium sp. Infections. (d) Empiric antifungal therapy in pts w/neutropenic fever. (e) Voriconazole may be useful in cryptococcus, blastomycosis, coccidiodomycosis, & histoplasmosis. Clinical data currently lacking to support routine use for these infections.
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(MIDII #68)
Discuss the ECHINOCANDINS => Caspofungin, Micafungin, Anidulafungin How do the echinocandins differ from other currently available antifungals? |
These drugs, unlike all other currently available antifungals, target the fungal CELL WALL rather than the fungal CELL MEMBRANE. Echinocandins are noncompetitive inhibitors of the β(1,3)-D-glucan synthase enyme which blocks the synthesis of β(1,3)-D-glucan, an essential component of the fungal cell wall. The chains of β(1,3)-D-glucan form a solid 3D matrix which gives the wall its shape and mechanical strength. Mechanism is both fungistatic and fungicidal. Fungistatic effect correlates to decreased cell wall synthesis and reduction in fungal growth. Fungicidal effect results from changes to the integrity of the cell wall. Mammalian cells do not contain β(1,3)-D-glucan so it should be selective against fungal cells.
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(MIDII #69)
Discuss the ECHINOCANDINS => Caspofungin, Micafungin, Anidulafungin => Mechanisms of Resistance and Spectrum of Activity |
(MOR): Little is known about resistance to echinocandins. Potential mechanisms include: (a) mutations in FKS gene coding for the catalytic subunit (Fks p) of β(1,3)-D-glucan synthase which binds intracellular UDP-glucose and a regulatory subunit Rho 1 p (binds intracellular GTP); and (b) mutations in the Rho 01 gene coding for the reg subunit of β(1,3)-D-glucan synthase.
(SPECTRUM): Active primarily against Candida sp. (fungicidal), including azole resistant or amphotericin resistant strains, and Aspergillus sp. (fungistatic). Not active against Cryptococcus neoformans. Echinocandin activity against filamentous fungi varies. In vitro, echinocandins are active against Paecilomyces variotii, but not Paecilomyces lilacinus and are active against Scedosporium apiospermum but not Scedosporium prolificans. Echinocandins are NOT active against Fusarium sp and mucormycosis. Active against Blastomyces dermatitidis and Histoplasma capsulatum, but Sporothrix schenckii is less susceptible. |
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(MIDII #70)
Discuss the ECHINOCANDINS => Caspofungin, Micafungin, Anidulafungin => Pharmacokinetics, Toxicities, and Clinical Uses |
(Pharm): Echinocandins are only available as IV formulations. High levels in kidneys, liver, spleen & lungs. Lower levels in brain. Mainly eliminated in urine & feces as metabolites. Metabolism is independent of the CYP450 system. Do NOT inhibit CYP450 enzymes. Plasma clearance is det'd by rate of distribution into tissues. T ½ = 9-15 hrs for caspofungin/micafungin & 40-50 hrs for anidulafungin. (Toxicities): Extremely well tolerated w/little to no adverse effects. Fever, flushing, nausea, headache, vomiting, & infusion-related phlebitis were the most frequent adverse events seen in clinical trials. Elevations in serum transaminases may rarely occur. (Clinical Uses): (a) Treatment of infections due to Candida sp., especially azole & amphotericin resistant strains. (b) Approved for use in aspergillosis as salvage therapy (caspofungin). (c) Empiric antifungal therapy in pts w/neutropenic fever (caspofungin). (d) Prophylaxis of Candida sp. infections in stem cell transplant recipients (micafungin). (e) Less or limited efficacy has been shown for other pathogens. (f) Clinically useful in combo w/ amphotericin or voriconaole for synergy in Rx of severe, invasive fungal infections (e.g. Invasive aspergillosis).
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(MIDII #71)
Discuss the Anti-Tuberculosis Agents => Primary goals of anti-TB therapy, 1st line agents, 2nd line agents, MOA |
(1)Primary goals of anti-TB therapy is to kill tubercle bacilli rapidly, prevent emergence of drug resistance, and eliminate persistent bacilli from host to prevent relapse. (2) Drugs can be divided into 1st and 2nd line. 1st line agents combine greatest efficacy w/an acceptable degree of toxicity. 2nd line agents are associated w/less efficacy, greater toxicity, or both. (3) Anti-TB drugs differ in MOAs and in their delivery to TB lesions. All first line agents (except ethambutol) are bactericidal. 4 of the 1st line agents (INH, rifampin, streptomycin, and ethambutol) are active against large populations of tubercle bacilli in cavities. Streptomycin, other aminoglycosides, & capreomycin penetrate cells poorly and are inactive at acidic pH. Pyrazinamide is active ONLY in acidic environments. Slowly replicating organisms in necrotic foci are killed by RIFAMPIN and less by INH.
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(MIDII #72)
Discuss ISONIAZID (INH) => Pharmacology |
1st line anti-TB drug. Isoniazid is indicated for all forms of TB. (MOA): Inhibits mycolic acid synthesis, an impt component of mycobacterial cell wall. Bactericidal against actively growing MTB; bacteriostatic against nonreplicating organisms. (MOR): Low level resistance is associated w/point mutations or short deletions in the catalase-peroxidase gene (katG). High level resistance is associated w/major deletions within the gene with most enzymatic activity. Resistance may develop in a 2nd gene involved in mycolic acid synthesis (inhA).
(Pharm): Well absorbed orally or IM. CSF levels: 20% of plasma levels & higher w/inflamed meninges. Metabolized in the liver by N-acetyltransferase. Consider reducing the dose in “slow” acetylators with severe hepatic dysfunction, who exhibit higher levels of INH. (Adverse Effects): (1) Increase serum transaminases (AST, ALT) in 12-15% , hepatotoxicity (1%) => Watch for RUQ pain, dark urine, jaundice. Discourage alcohol use. (2) Peripheral neuropathy => burning, tingling, numbness. Coadminister vit B6. Alcoholics, children, diabetics, & malnourished at ↑ risk. (Drug Interactions): (a) Phenytoin => watch for mental status changes, nystagmus, and ataxia. (b) Rifampin => ↑ risk of hepatotoxicity (20-30%). |
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(MIDII #73)
Discuss RIFAMPIN => Pharmacology |
1st line anti-TB drug. Rifampin is indicated for all forms of TB. (MOA): Inhibits DNA-dependent RNA polymerase. Bactericidal. (MOR): Resistance results from a point mutation or deletion within the region encoding the β subunit of RNA polymerase.
(PHARM): Well absorbed orally. CSF levels: 50% of plasma levels w/inflamed meninges. Deacetylated in the liver to an active form which undergoes biliary excretion & enterohepatic recirculation. Severe liver dysfunction req's a dosage reduction. (Adverse Effects): (1) ↑ in hepatic enzymes (AST, ALT, bilirubin, alkaline phosphatase) 10-15%. Hepatotoxicity (1%) => Watch for RUQ pain, dark urine, jaundice. Alcoholics at ↑ risk. (2) Rash, GI disturbances. (3) Orange discoloration of body fluids => urine, tears, sweat, soft contact lenses, etc. (4) Flu-like syndrome => fever, joint pain, muscle cramps. (Drug Interactions): Interacts w/ >100 drugs => always think drug interactions. DO NOT COADMINISTER protease inhibitors. Rifampin ↓ Cx's of these drugs when coadministered: fluconazole, itraconazole, warfarin, digoxin, metoprolol, quinidine, verapamil, oral contraceptives, cyclosporine, diazepam, haloperidol, methadone, phenytoin, sulfonylureas. |
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(MIDII #74)
Discuss PYRAZINAMIDE (PZA) => Pharmacology |
1st line anti-TB drug. PZA is a req'd component of a 6-month short course x 2 months. Unknown MOA. Bactericidal w/optimal activity against semidormant organisms in an acidic environment. (MOR): Resistance results from mutations in the gene encoding pyrazinamidase (pncA) which converts PZA to the active form of pyrazinoic acid.
(Pharm): Well absorbed orally. Achieves adequate levels in CSF. Metabolized in the liver but metabolites are excreted by the kidneys. Dosage modification in renal dysfunction is necessary. (Adverse Effects): (1) Nausea/vomiting. (2) Hepatotoxicity (↑ liver enzymes) => watch for RUQ pain, dark urine, jaundice. Preexisting liver disease and higher doses ↑ risk. (3) Hyperuricemia => potential for exacerbation of gout. |
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(MIDII #75)
Discuss ETHAMBUTOL => Pharmacology |
1st line anti-TB drug. Ethambutol is commonly used as the 4th drug in RIPE and often in regimens w/isolates resistant to INH or rifampin. (MOA): Inhibits arabinosyl transferase enzymes involved w/synthesis of arabinogalactan and lipoarabinomannan within the cell wall. Bacteriostatic. (MOR): Resistance results from point mutations in the arabinosyl transferase enzyme EmbB, which is coded by the embB gene.
(Pharm): Well absorbed (75-80%). Distributes into CSF. Predominantly excreted via kidneys. Dosage reduction necessary in renal dysfunction. (Adverse Effects): (1) Neuropathy (optic neuritis) => Complaints of blurry vision or inability to see the color green (more common at higher doses). (2) Hyperuricemia => potential for exacerbation of gout. (3) Rash |
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Discuss STREPTOMYCIN => Pharmacology
1st line anti-TB drug. Streptomycin is used as the 4th drug in patients at significant risk of drug resistance or in regimens with known drug resistance. (MOA): Inhibits protein synthesis. Bactericidal. (MOR): Resistance is associated w/mutational changes involving ribosomal binding protein or the ribosomal binding site (gene rpsL). 16-S ribosomal RNA gene. |
(PHARM): Administered IV or IM. Does not reach reliable Cx's in the CSF. Eliminated via the kidneys. Dosage reduction necessary in pts w/renal dysfunction as well as those w/low body wt or age >50 yrs. T ½ = 1.5-3.5 hrs in pts w/normal renal function. (Adverse Effects): (1) Vestibular toxicity => complaints of tinnitis, ↓ hearing, problems w/balance. (2) Renal toxicity (<1%) => ↓ urine output, ↑ serum creatinine levels. (3) Pain at injection site.
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(MIDII #77)
Discuss RIFABUTIN => Pharmacology 2nd line anti-TB drug. Rifabutin is as effective as rifampin. Used in pts w/HIV receiving protease inhibitors b/c it has less effect on their metabolism. (MOA): Inhibits RNA polymerase. Bactericidal. (MOR): Resistance results from a point mutation or deletion within the RNA polymerase. |
(PHARM): Well absorbed. Long plasma half-life and good distribution into tissues. (Adverse Effects): (1) Uveitis => complaints of ocular pain & blurred vision. (2) Polymyalgia syndrome (pseudojaundice) => yellowish-tan discoloration of the skin. (3) Hepatitis (↑ liver enzymes) => watch for RUQ pain, dark urine, jaundice. (4) Rash, GI. (5) May discolor body fluids orange => includes urine, sweat, tears, soft contact lenses, etc. (Drug Interactions): (a) Rifabutin ↓ plasma Cx's of these agents (to a lesser degree than Rifampin): verapamil, methadone, digoxin, cyclosporine, corticosteroids, oral anticoagulants (warfarin), theophylline, barbiturates, ketoconazole, oral contraceptives, quinidine, protease inh, NNRTIs. (b) Indinavir, ritonavir, nelfinavir ↑ Cx of Rifabutin (↓ dose of Rifabutin). (c) DO NOT COADMINISTER rifabutin w/ delavirdine as it ↓ concentrations of delavirdine.
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(MIDII #78)
Discuss QUINOLONES => Pharmacology 2nd Line anti-TB agents. Quinolones (levofloxacin, moxifloxacin) are incorporated into regiments for multi-drug resistant TB. (MOA): Inhibits DNA gyrase. Some bactericidal. (MOR): Resistance results from mutations in the genes responsible for DNA configuration (DNA gyrase). |
(PHARM): Available IV and orally. Well absorbed orally. Distribute well throughout body w/variable penetration into the CSF. Most quinolones are excreted by the kidneys (except moxifloxacin) and require dosage modification in renal dysfunction. (Adverse Effects): (1) GI => nausea, vomiting, diarrhea, abdominal pain. (2) CNS effects => dizziness, insomnia, irritability, anxiety, seizures. (3) Rashes and photosensitivity. (Drug Interactions): (a) Antacids (Al, Ca, Mg-containing), iron result in a significant ↓ in absorption of the quinolones. Separate oral administration times by 2 hrs. (b) Quinolones may inhibit metabolism of warfarin. Watch for ↑ INR, bruising, bleeding. (c) ↓ theophylline metabolism.
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(MIDII #79)
Discuss CAPREOMYCIN |
2nd line anti-TB agent. Capreomycin is used in regimens w/MDR-TB resistant to streptomycin. (MOA): Inhibits cell wall synthesis. (MOR): unknown. (PHARM): IM injection. Excreted via the kidneys. (Adverse Effects): (1) hearing loss, tinnitus. (2) renal dysfunction => ↓ urine output, ↑ serum creatinine levels.
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(MIDII #80)
Discuss AMIKACIN, KANAMYCIN |
2nd line anti-TB agents. Amikacin is used as an alternative to streptomycin and capreomycin in regimens for MDR-TB. (MOA): Inhibits protein synthesis. (MOR): Resistance results from an A to G change at base pair 1408 of the 16-S ribosomal RNA gene. (Pharm): Administered IV or IM. Does not reach reliable Cx's in the CSF. Eliminated via the kidneys. Dosage reduction necessary in pts w/renal dysfunction. (Adverse Effects): (1) Renal toxicity => ↓ urine output, ↑ serum creatinine levels. (2) Hearing loss, tinnitus.
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(MIDII #81)
Discuss Para-aminosalicylic Acid (PAS) |
2nd line anti-TB drug. Use is limited to MDR-TB. (MOA): Inhibits folate synthesis. Bacteriostatic. (Pharm): Incompletely absorbed orally. Distributes well except for CSF (10-50%). Primarily eliminated via kidneys. Dosage adjustment necessary in renal dysfunction. (Adverse Effects): (1) GI => often results in poor compliance. (2) Hepatotoxicity. (3) Hypothyroidism => thyroid hormone replacement may be necessary.
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(MIDII #82)
Discuss CYCLOSERINE |
2nd line anti-TB drug. Alternative in a regimen for MDR-TB. (MOA): Inhibits cell wall synthesis. Bacteriostatic. (MOR): Resistance sometimes mediated by reduced uptake into the cell. (Pharm): Well absorbed orally. Distributes throughout the body including the CSF. Primarily excreted via the kidneys. (Adverse Effects): (1) Peripheral neuropathy. (2) CNS dysfunction => confusion, irritability, somnolence, headache, nervousness, vertigo, seizures.
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(MIDII #83)
Discuss ETHIONAMIDE |
2nd line anti-TB drug. Alternative in a regimen for MDR-TB. (MOA): inhibits mycolic acid synthesis. Bacteriostatic. (MOR): Unknown. (PHARM): Well absorbed orally. Widely distributed including the CSF. Metabolized in the liver w/metabolites excreted renally. (Adverse Effects): (1) Nausea, vomiting. (2) Peripheral neuropathy => burning, tingling, numbness. (3) Psychiatric disturbances. (4) Hepatotoxicity w/increased liver enzymes => watch for RUQ pain, dark urine, jaundice. (5) Poor glycemic control =>↑ glucose, ↑ need for insulin in diabetics.
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(MIDII #84)
Definition: VIRUS PARTICLE or VIRION |
An infectious agent composed of nucleic acid (RNA or DNA), a protein shell (capsid), and, in some cases, a lipid envelope. Virions have full capacity for replication when a susceptible target cell is encountered.
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(MIDII #85)
Definition: CAPSID and CAPSOMERES |
The protein coat that surrounds the viral nucleic acid is called a capsid. This is composed of repeating protein subunits called capsomeres. Generally, capsids have either helical or icosahedral symmetry.
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(MIDII #86)
Definition: NUCLEOCAPSID |
The complete protein-nucleic acid complex of a virus is called a nucleocapsid.
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(MIDII #87)
Definition: SATELLITE or DEFECTIVE VIRUSES |
Viruses which require a second virus (helper virus) for replication. Hepatitis delta virus is the major human pathogen example. It requires the presence of hepatitis B virus to complete its replication cycle.
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(MIDII #88)
Definition: VIROIDS |
Viroids are the smallest known autonomously replicating molecules. They consist of single-stranded, circular RNA, 240-375 residues in length. They are plant pathogens.
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(MIDII #89)
Definition: PRIONS |
Prions are not viruses but are often discussed within this microbiologic category. Prions are infectious protein molecules that contain no definable nucleic acid and are responsible for the transmissible and familial spongiform encephalopathies: Creutzfeldt-Jakob disease, kuru, fatal familial insomnia, Gerstmann-Straussler-Sheinker syndrome, and bovine spongiform encephalopathy (“mad cow disease”). The pathogenic prion protein (PrP^Sc) is formed from a normal human protein (PrP^C) through post-translational processing.
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(MIDII #90)
Discuss viral classification => Modern classification of viruses is based upon what 3 characteristics of viruses? |
(1) Type of viral nucleic acid (RNA or DNA, single-stranded or double-stranded) and its replication strategy.
(2) Capsid symmetry (icosahedral or helical). (3) Presence or absence of a lipid envelope. |
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(MIDII #91)
Discuss Pathogenesis of Viral Diseases => Outcome of a particular virus w/human host is dependent on pathogen and host factors. Viral strains within a genus may have different cell tropisms, replication capacities, and cytopathogenic effects. Name the five key elements of the virus-host interaction and the net results of this interaction. |
Key elements: (1) Viral strain; (2) Inoculum size; (3) Route of exposure; (4) Susceptibility of host (i.e., is there preexistent immunity from past exposure or vaccination?); (5) Immune status and age of host.
Net result of virus-host interaction: (1) No infection; (2) Abortive infection w/limited viral replication; (3) Asymptomatic infection; (4) Symptomatic infection; (5) Depending upon the agent and the immune status of the host, persistent/latent or self-limited infection. |
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(MIDII #92)
Pathogenic Steps in Human Infection: Provide a generalized schema of viral infection leading to disease in the human host. |
(1)Virus enters thru skin, mucous membranes, respiratory tract, GI tract, via a transfusion or transplanted organ or via maternal-fetal transmission. (2) Local replication occurs at site of inoculation. Certain agents exhibit pathology at the skin or mucous membrane surface (e.g., HSV, HPV). (3) For some neurotropic viruses there may be spread along peripheral nerve routes to ganglia (e.g., HSV) or the CNS (e.g. Rabies virus). For other neurotropic agents, the CNS is seeded following viremia. (4) For many agents there is replication in regional lymph nodes w/subsequent viremia and spread to target organs. Some viruses travel in the bloodstream free in the plasma (e.g. Picornaviruses); others are cell-associated (e.g., cytomegalovirus). (5) Replication in target organs may lead to local damage and further rounds of viremia. (6) Non-specific and specific host immune responses come into play to try to control and downregulate the viral replicative process.
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(MIDII #93)
Immune Responses to Viral Infections => Non-specific Immunity, Specific Immunity, and Intense Immunologic Rxns |
(1)Non-specific immunity => elements of the immune system that can clear virus or virally infected cells immediately upon or shortly after viral exposure and which are NOT dependent on immunologic memory. Non-specific immunity may include: (a) Phagocytic cells like PMNs, Mfs and monocytes, (b) Cytokines (IFNs) and Chemokines, (c) NK cells, (d) Poorly defined antiviral factors may exist in blood or body fluids. (2) Specific immunity => antigen specific B and T cell responses that lead to development of Abs, cytotoxic T cells and Ab-dependent cellular cytotoxicity (ADCC). (3) sometimes an intense immunologic rxn to a viral agent can result in immunopathology and a serious clinical syndrome. Example: dengue hemorrhagic fever which is likely due to Ab-dependent enhancement and T cell activation on re-exposure to the dengue virus.
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(MIDII #94)
Mechanisms of Viral Persistence => Chronic Persistent Infection and Latent Infection |
(1)Viruses may cause chronic, persistent infection w/continuous viral replication in face of an immune response. Examples: HIV, hep B and C viruses. Some viruses may demonstrate persistent infection in immune compromised hosts, including herpesviruses, human papillomavirus, and rubella virus. (2) Latent infection is characterized by a quiescent or minimally transcriptionally active viral genome w/periods of reactivation. Examples: herpesviruses (cytomegalovirus, Epstein-Barr virus, herpes simplex virus, varicella-zoster virus), human papillomavirus, human retroviruses. Recurrent herpes labialis or genital herpes due to HSV or herpes zoster due to varicella zoster virus are examples of latency & reactivation. Viruses which exhibit latency may exhibit chronic, persistent replication in the setting of immune compromised host.
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(MIDII #95)
Mechanisms of Viral Persistence => How do viruses go about producing chronic infections? What mechanisms of persistence do they employ? What are sites of persistent viral infection? |
Mechanisms of persistence include antigenic variation to escape Ab or cytotoxic T cell responses, downregulation of Class I MHC resulting in diminished recognition by cytotoxic T cells and modulation of apoptosis. Viruses which establish latent infection escape recognition by the immune system thru decreased viral antigen expression and presentation.
Sites of persistence include the nervous system (herpes simplex virus, varicella zoster virus, measles virus, poliovirus, JC virus), the liver (hepatitis B virus, hepatitis C virus), and leukocytes (HIV, cytomegalovirus, Epstein-Barr virus). |
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(MIDII #96)
Discuss the association of certain viruses with oncogenesis. |
Several viruses are associated with human cancers, including: (a) Epstein-Barr Virus w/lymphoma, nasopharyngeal carcinoma, & leiomyosarcoma; (b) herpesvirus 8 w/ Kaposi's sarcoma and body cavity B-cell lymphoma; (c) hepatitis B and C viruses w/hepatocellular carcinoma; (d) human papillomavirus w/cervical cancer and anogenital carcinoma. Mechanisms of oncogenesis include transformation (EBV and herpesvirus 8) and binding of tumor suppressor proteins (HPV).
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(MIDII #97)
Diagnosis of Viral Infections => Methods to diagnose viral infections. (A) Dx of viral infection relies 1st on recognition of a distinct clinical syndrome (e.g. Herpes zoster infection) or a consideration of the viral infection in the differential diagnosis of a presenting syndrome (e.g., aseptic meningitis). (B) The 2nd consideration is knowledge of appropriate specimens to send out to the laboratory (blood, body fluids, lesion scraping, tissue) to diagnose a particular infection. Remember that isolation of viruses relies on use of proper viral transport medium and quick delivery to the lab. (C) A variety of methods exist to diagnose viral infections. Discuss these! |
(1)Isolation of virus in tissue culture, animals, embryonated eggs. Most diagnostic labs only use tissue culture to isolate viruses. A specific cytopathic effect or induction of a characteristic function (e.g., hemagglutination) can indicate growth of viruses in tissue culture. Can be confirmed w/virus-specific antisera applied to the tissue monolayer linked to a tissue stain or to neutralize the cytopathic effect or hemagglutination. (2) Ag detection in body fluids (e.g. Respiratory tract for respiratory viruses) or blood (e.g., cytomegalovirus) or lesion scrapings (for HSV or varicella-zoster virus) w/specific immune sera linked to fluorescence or enzyme immunoassay detection. (3) PCR amplification and/or nucleic acid probes to detect viral nucleic acid in body fluids or tissues. (4) Ab detection. IgM Ab detection can assist w/acute diagnosis. 4X rises in IgG specific Ab or conversion from seronegative status to seropositive status can secure a Dx. Not helpful in an acute setting. (5) Examination of tissue samples by light microscopy for viral induced cytopathology and Ag detection by immunohistochemical staining. (6) Examination of body fluids or tissues by electron microscopy. Not efficient. Depends on LOTS of virions present to permit detection.
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(MIDII #98)
Prevention and Therapy for Viral Infections |
(A) Vaccines => Eradication of smallpox occurred thru a vaccine. Effective vaccines exist for polio, mumps, measles, rubella, influenza, hepatitis A, hepatitis B, varicella-zoster, rabies, adenovirus, Japanese B encephalitis and yellow fever. (B) Immune globulin can prevent or ameliorate clinical disease due to certain viral agents. Examples: varicella-zoster immune globulin for exposure in immune compromised hosts, rabies immune globulin (administered w/rabies vaccine) following an exposure, CMV immune globulin for transplant recipients, respiratory syncytial virus immune globulin and immune serum globulin for hepatitis A. (C) Screening of blood for prevention of transmission of HIV, hep B and C, and CMV in certain transplant situations. (D) Safe sexual practices for prevention of HIV, Hep B and HPV infection. (E) Advances in specific antiviral therapy over the past 30 yrs have been marked. Effective therapy exists for: HSV, varicella-zoster virus, cytomegalovirus (CMV), HIV, influenza virus, RSV (respiratory syncytial virus), hepatitis B and hepatitis C.
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(MIDII #99)
STEPS IN VIRAL REPLICATION: Step 1 => Attachment |
This is the first step in viral replication. Surface proteins of the virus interact w/specific receptors on the target cell surface. These may be specialized proteins w/limited distribution or molecules that are more widely distributed on tissues throughout the body. Presence of a virus-specific receptor is necessary but not sufficient for viruses to infect cells and complete the replicative cycle.
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(MIDII #100)
STEPS IN VIRAL REPLICATION: Step 2 => Penetration |
Enveloped viruses (e.g., HIV, influenza virus) penetrate cells through fusion of the viral envelope w/the host cell membrane. Non-enveloped viruses penetrate cells by translocation of the virion across the host cell membrane or receptor mediated endocytosis of the virion in clathrin coated pits w/accumulation of viruses in cytoplasmic vesicles.
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(MIDII #101)
STEPS IN VIRAL REPLICATION: Step 3 => Uncoating (disassembly) |
A complex process which differs by taxonomic class and is not fully understood for many agents. This process makes the nucleic acid available for transcription to permit multiplication of the virus.
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(MIDII #102)
STEPS IN VIRAL REPLICATION: Step 4 => Transcription and Translation |
The key to understanding the genomic expression of viruses is noting the fact that viruses must use HOST cellular machinery to replicate and make functional and structural proteins.
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(MIDII #103)
STEPS IN VIRAL REPLICATION: Step 5 => Assembly and Release |
The process of virion assembly involves bringing together newly formed viral nucleic acid and the structural proteins to form the nucleocapsid of the virus. There are basically 3 strategies that viruses employ: (1) Non-enveloped viruses exhibit full maturation in the cytoplasm (e.g. Picornaviruses) or the nucleus (e.g. Adenoviruses) w/disintegration of the cell & release of virions. (2) For enveloped viruses, including (-) strand RNA viruses, the (+) strand togaviruses, & retroviruses, final maturation of the virion takes place as the virion exits the cell. Viral proteins are inserted into the host cell membrane. Nucleocapsids bind to the regions of the host cell membranes w/tehse inserted proteins and bud into the extracellular space. Further cleavage & maturation of proteins may occur after viral extrusion to impart full infectivity on the virion. Viruses differ in their degree of cytolytic activity. (3) Herpesviruses (which are enveloped) assemble their nucleocapsids in the nuclei of infected cells and mature at the inner lamella of the nuclear membrane. Virions accumulate in this region, in the ER and in vesicles protected from the cytoplasm. Release of virions from the cell surface is associated w/cytolysis.
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(MIDII #104)
Strategies of Genomic Expression => Positive (+) Strand RNA Viruses Coding for One Genome-Sized mRNA [e.g., poliovirus, flaviviruses including hep C virus] |
(1)Genomic RNA binds to ribosomes and is translated into a polyprotein. (2) Polyprotein is cleaved. (3) Genomic RNA's serve as templates for synthesis of complementary full length (-) strand RNA's by a viral polymerase. (4) (-) strand RNA serves as a template for (+) strand RNAs. These (+) strands can serve to produce more polyprotein, more (-) strand RNAs or as part of new virions which are forming.
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(MIDII #105)
Strategies of Genomic Expression => Positive (+) Strand RNA Viruses Coding for Subgenomic RNA's (e.g. Togaviruses) |
(1)Genomic RNA binds to ribosomes but only a portion of the 5' end is translated into non-structural proteins.
(2) (-) strand RNA is synthesized. Different size classes of (+) RNAs are produced. One is translated into a polyprotein which is cleaved to form structural proteins. Another is full length and serves as genomic RNA for new virions which are forming. |
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(MIDII #106)
Strategies of Genomic Expression => Single Strand RNA Viruses with 2 Identical Strands (e.g., retroviruses) |
(1) Genomic RNA serves as a template for production of DNA copy. This is produced by an RNA-dependent DNA polymerase (reverse transcriptase) contained in the virion. (2) Digestion of genomic RNA and synthesis of second, complementary DNA strands then proceeds. (3) Double-stranded DNA migrates to the nucleus and integrates into the host cell genome. (4) Integrated DNA may remain silent or be transcribed into genomic, full-length RNA or shorter, spliced RNA's. The latter code for accessory and structural proteins. Full-length RNA transcripts are packaged into forming virions.
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(MIDII #107)
Strategies of Genomic Expression => Negative (-) Strand Nonsegmented RNA Viruses (e.g. Paramyxoviruses, rhabdoviruses, filoviruses) |
(1)Transcription of (-) strand occurs after entry and is mediated by virion packaged transcriptase.
(2) (+) strand RNAs are produced; proteins are synthesized. (3) Full-length (-) strand RNA's are produced and packaged into newly forming virions. (4) Transcription and translation take place entirely in the cytoplasm of infected cells. |
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(MIDII #108)
Strategies of Genomic Expression => Negative (-) Strand Segmented RNA Viruses (e.g.bunyaviruses and orthomyxoviruses) |
(1) mRNAs are synthesized from each segment. (2) Viral proteins are synthesized. (3) (+) strand RNAs are synthesized and serve as templates for (-) strand genomic RNAs.
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(MIDII #109)
Strategies of Genomic Expression => Double Stranded RNA Viruses (e.g., reoviruses) |
(1)Genome is transcribed by virion packaged polymerase. Messenger RNAs (mRNAs) are translated to viral proteins or transcribed to complementary strands to yield double stranded RNA genomes for new virion formation.
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(MIDII #110)
Strategies of Genomic Expression => Double Stranded DNA Viruses Which Replicate in Nucleus (e.g., papovaviruses, papillomaviruses, adenoviruses, herpesviruses). |
(1)Sequential, ordered rounds of mRNA and protein production regulate replication.
(2) Structural proteins produced during last cycle of transcription. |
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(MIDII #111)
Strategies of Genomic Expression => Single-Stranded DNA Viruses (e.g., parvoviruses) |
(1)Complementary DNA strand synthesized in nucleus.
(2) Transcription of the genome ensues. |
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(MIDII #112)
Strategies of Genomic Expression => Partially Double Stranded DNA Viruses (hepadnaviruses) |
(1) Genome of hepatitis B is circular and partially double stranded; it is replicated in the nucleus.
(2) Genome is converted to a closed circular molecule by a DNA polymerase which is virion packaged. (3) 2 classes of RNA species are produced: one that codes for viral proteins and one that serves to produce genomic DNA by a virally encoded reverse transcriptase. |
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(MIDII #113)
What three requirements must be satisfied to ensure successful viral infection in an individual host? |
(1)Sufficient virus must be available to initiate infection. (2) Cells at the site of infection must be accessible, susceptible, and permissive for the virus. (3) Local host anti-viral defense systems must be absent or initially ineffective.
To infect its host, a virus must first enter cells at a body surface. Common sites of entry include the mucosal linings of the respiratory, alimentary, and urogenital tracts, the outer surface of the eye (conjunctival membranes or cornea) and the skin. |
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(MIDII #114)
Discuss viral entry through the Respiratory Tract (RT) |
Respiratory tract (RT) => most common route of viral entry. 140 m^2 of absorptive area in human lung. 6 L of air per min are exchanged, introducing large #'s of foreign particles & aerosolized droplets into the lungs w/each breath. Many of these particles/droplets contain viruses. Mechanical barriers play significant role in anti-viral defense. Tract is lined w/mucociliary blanket: ciliated cells, mucous-secreting goblet cells, sub-epithelial mucous-secreting glands. Foreign particles deposited in the nasal cavity or upper RT are trapped in mucus, carried to the back of the throat & swallowed. Lower RT: particles trapped in mucus are brought up from the lungs to the throat by ciliary action. Lowest portions of the RT (alveoli) lack cilia or mucus but MΦs lining the alveoli ingest & destroy particles. Other cellular & humoral immune responses also intervene. Viruses enter the RT as aerosolized droplets expelled by an infected individual by coughing/sneezing, or through contact w/saliva from an infected individual. Larger virus-containing droplets are deposited in the nose, while smaller droplets find their way into the airways or the alveoli. To successfully infect the respiratory tract, viruses must NOT be swept away by mucus, neutralized by Ab, or destroyed by alveolar MΦs.
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(MIDII #115)
Discuss viral entry through the Alimentary Tract (AT): |
The alimentary tract (AT) is a common route of infection & dispersal. Eating, drinking & kissing/sex place viruses in the AT, which is designed to mix, digest & absorb food. Good opportunity for viruses to encounter susceptible cells & interact w/cells of the circulatory, lymphatic, & immune systems. Extremely hostile environment. Stomach is acidic, intestine is alkaline, digestive enzymes & bile detergents abound, mucus lines the epithelium, lumenal surfaces of intestines contain Abs & phagocytic cells. Viruses that infect via intestinal rte must be resistant to extremes of pH, proteases, & bile detergents. Viruses lacking those features are destroyed when exposed to the alimentary tract – must infect at other sites.
The entire intestinal surface is covered w/columnar villous epithelial cells w/apical surfaces densely packed w/microvilli. Brush border, together w/surface coat of glycoproteins & glycolipids and the overlying mucous layer, is permeable to electrolytes & nutrients but presents a formidable barrier to microorganisms. However, enteric adenoviruses & Norwalk virus (a calicivirus) replicate extensively in intestinal epithelial cells. Mechanisms by which they bypass physical barriers & enter susceptible cells are not well understood. Scattered throughout intestinal mucosa are lymphoid follicles covered on the lumenal side w/follicle-associated epithelium consisting of columnar absorptive cells and M cells. M-cell transcytosis provides mechanism by which some enteric viruses enter deeper tissues of the host from the intestinal lumen. |
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(MIDII #116)
How does the hostile environment of the Alimentary Tract facilitate infection by some viruses? |
Reovirus particles are converted by host proteases in the intestinal lumen into infectious subviral particles which subsequently infect intestinal cells. Most enveloped viruses do not initiate infection in the alimentary tract b/c viral envelopes are susceptible to dissociation by detergents (such as bile salts). Enteric coronaviruses are notable exceptions => not known why these enveloped viruses can withstand the harsh conditions of the alimentary tract.
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(MIDII #117)
Discuss viral entry through the Urogenital Tract. |
Some viruses enter the urogenital tract as the result of sexual activities. UG tract is well-protected by physical barriers including mucus & low pH (vagina). Normal sexual activity can result in minute tears or abrasions in the vaginal epithelium or urethra, allowing viruses to enter. Some viruses infect the epithelium and produce local lesions (HPV => genital warts). Other viruses access cells in the underlying tissues and infect cells of the immune system (HIV type 1) or sensory and autonomic neurons (herpes simplex virus).
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(MIDII #118)
Discuss viral entry through the eyes. |
The epithelium covering the exposed part of the sclera & conjunctivae is the route of entry for several viruses. Every few seconds the eyelid passes over the sclera, bathing it in secretions that wash away foreign particles. Little opportunity for viral infection of the eye, unless it is injured by abrasion. Direct inoculation into the eye may occur during ophthalmologic procedures or from environmental contamination (e.g. improperly sanitized swimming pools). Usually replication is localized and results in inflammation of the conjunctiva (conjunctivitis). Systemic spread of the virus from the eye is rare but does occur. Herpesviruses can infect the cornea at the site of a scratch or other injury, which can lead to immune destruction of the cornea & blindness.
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Discuss viral entry through the skin.
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Skin is an effective barrier against viral infections as the dead outer layer cannot support viral growth. Entry occurs when skin's integrity is breached through breaks or punctures. Replication is limited to the site of entry b/c the epidermis is devoid of blood or lymphatic vessels that could provide pathways for further spread. Other viruses gain entry to vascularized dermis through bites of arthropod vectors such as mosquitoes, mites, ticks, & sandflies. Deeper inoculation into the tissue & muscle below the dermis can occur by hypodermic needle punctures, body piercing or tattooing, animal bites, or sexual contact when body fluids are mingled through skin abrasions or ulcerations. Viruses that initiate infection in dermal or sub-dermal tissue can reach nearby blood vessels, lymphatic tissues, and cells of the nervous system. So they can spread to other sites in the body.
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(MIDII #120)
Discuss viral spread => What are disseminated infections? Systemic? |
After replication at site of entry, virus particles can remain localized or can spread to other tissues. Local spread of infection in the epithelium occurs when newly released virus infects adjacent cells. Infections are contained by the physical constraints of the tissue and brought under control by intrinsic & immune defenses. Infection that spreads beyond the primary site of infection is called DISSEMINATED. If many organs become infected, the infection is described as systemic. For an infection to spread beyond the primary site, physical and immune barriers must be breached. After crossing the epithelium, virus particles reach the basement membrane (bm). Integrity of the bm may be compromised by epithelial cell destruction & inflammation. Below the bm are sub-epithelial tissues where the virus encounters tissue fluids, the lymphatic system, & phagocytes. These play an impt role in clearing foreign particles but may disseminate infectious virus from the primary site of infection.
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(MIDII #121)
Discuss the directional release of viral particles from polarized cells at the mucosal surface, an important mechanism for avoiding local host defenses and facilitating spread within the body. |
Virions can be released from the apical surface, from the basolateral surface, or from both. After replication, virus released from the apical surface is outside the host. Such directional release facilitates the dispersal of many newly replicated enteric viruses in the feces (e.g., poliovirus). Virus particles released from the basolateral surfaces of polarized epithelial cells have been moved away from the defenses of the lumenal surface. Directional release is therefore a major determinant of the infection pattern. Generally, viruses released at apical membranes establish a localized or limited infection, while release of viruses at the basal membrane provides access to the underlying tissues and may facilitate systemic spread.
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(MIDII #122)
Discuss Hematogenous Spread of Viruses |
Viruses that escape from local defenses often do so by entering the bloodstream. Virus particles may enter the blood directly thru capillaries, by replicating in endothelial cells, or thru inoculation by a vector bite. Once in the blood, viruses may access almost every tissue in the host. Hematogenous spread begins when newly replicated particles produced at the entry site are released into the extracellular fluids which can be taken up by the local lymphatics. Lymphatic capillaries are more permeable than circulatory system capillaries, facilitating viral entry. Since lymphatic vessels ultimately join the venous system, virus particles in the lymph have free access to the bloodstream. Virions pass through lymph nodes in the lymphatics, where they encounter migratory cells of the immune system. Viral pathogenesis resulting from direct infection of immune cells (HIV, measles) initiates this way. Some viruses replicate in infected lymphoid cells. Progeny are released into the blood plasma. Infected lymphoid cells may migrate away from the local lymph node to distant parts of the circulatory system.
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(MIDII #123)
What is Viremia? Active Viremia? Passive Viremia? Primary Viremia? Secondary Viremia? |
(1)VIREMIA refers to presence of infectious virus particles in the blood. May be free in the blood or contained within infected cells (lymphocytes). (2) ACTIVE VIREMIA is produced by virus replication, while (3) PASSIVE VIREMIA results when viral particles are introduced into the blood w/o viral replication at the site of entry (injection of a viral suspension into a vein). (4) Progeny virions released into the blood after initial replication at the site of entry constitute PRIMARY VIREMIA. Cx of virus particles during primary viremia is low. (5) Subsequent disseminated infections that result are often extensive, releasing considerably more virus particles. Delayed appearance of a high Cx of infectious virus in the blood is termed SECONDARY VIREMIA.
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(MIDII #124)
How is viremia helpful in a diagnostic sense? What practical problems can ensue from viremia? |
Viremias are of diagnostic value and can be used to monitor the course of an infection, but they also present practical problems. Infections can be spread inadvertently in the population when pooled blood from thousands of individuals is used directly for therapeutic purposes (transfusions) or as a source of therapeutic proteins (e.g., gamma globulin or blood-clotting factors).
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(MIDII #125)
Discuss the neural spread of viruses. |
Many viruses spread from the primary site of infection by entering local nerve endings. For some virsues (rabies virus, alpha herpesviruses), neuronal spread is the definitive characteristic of their pathogenesis. For other viruses (poliovirus & reovirus), invasion of the nervous system is a less frequent diversion from their site of replication & destination. Some viruses (mumps, HIV, measles virus) may replicate in the brain but spread by a hematogenous route. Because protein synthesis does not occur in the extended processes of neuronal cells, virus particles must be transported over relatively long distances to the site of viral replication. All evidence indicates that viruses are carried in the infected neuron by cellular systems, but viral proteins may facilitate the direction of spread.
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(MIDII #126)
Discuss Viral Spread to the CNS: Neural, Olfactory, & Hematogenous |
(1)NEURAL: Poliovirus, yellow fever virus, mouse hepatitis virus, Venezuelan encephalitis virus, rabies virus, reovirus, herpes simplex virus (HSV) types 1 & 2, pseudorabies virus
(2)OLFACTORY: Poliovirus (experimental), HSV, coronavirus (3)HEMATOGENOUS: Poliovirus, coxsackievirus, arenavirus, mumps virus, measles virus, HSV, cytomegalovirus |
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(MIDII #127)
What is a NEUROTROPIC virus? NEUROINVASIVE virus? NEUROVIRULENT virus? Give examples. |
(a) A NEUROTROPIC virus can infect neural cells. Infection may occur by neural or hematogenous spread initiating from a peripheral site.
(b) A NEUROINVASIVE virus can enter the CNS (spinal cord & brain) after infection of a peripheral site. (c) A NEUROVIRULENT virus can cause disease of nervous tissue, manifested by neurological symptoms and often death. Examples:(1) Herpes simplex virus has low neuroinvasiveness of the CNS but high neurovirulence. Always enters the peripheral nervous system but rarely enters the CNS. When it does, the consequences are almost always severe if not fatal. (2) Mumps has high neuroinvasiveness but low neurovirulence. Most infections lead to invasion of the CNS but neurological disease is mild. (3) Rabies virus has high neuroinvasiveness and high neurovirulence. Readily infects the peripheral nervous system and spreads to the CNS with 100% lethality unless antiviral therapy is administered shortly after infection. |
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(MIDII #128)
ORGAN INVASION => Once virions enter the blood and are dispersed from the primary site, any subsequent replication requires invasion of new cells & tissues. 3 main types of blood vessel-tissue junctions provide routes of tissue invasion. Discuss. |
3 types of blood vessel-tissue junctions are: capillary, venule, & sinusoid.
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(MIDII #129)
ORGAN INVASION => Skin |
In some systemic viral infections, rashes occur when virions leave blood vessels, producing different types of skin lesions: macules & papules when inflammation occurs in the dermis, w/inflammation confined in/near the vascular bed. Vesicles & pustules occur when viruses spread from capillaries to superficial layers of skin. Destruction of cells by virus replication is the primary cause of lesions.
Examples: (a) Coxsackievirus A 16 => hand-foot-and-mouth disease w/maculopapular rash; (b) Echoviruses 4, 6, 9, 16; Coxsackieviruses A9, 16, 23 => maculopapular rash; (c) Measles virus => maculopapular rash; (d) Parvovirus => erythema infectiosum w/maculopapular rash; (e) Rubella virus => German measles w/maculopapular rash; (f) Varicella-zoster virus => chickenpox, zoster (shingles) w/vesicular rash. |
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(MIDII #130)
ORGAN INVASION => Liver, Spleen, Bone Marrow & Adrenal Glands |
These tissues are characterized by presence of sinusoids lined with MФs (reticuloendothelial system) to filter the blood & remove foreign particles. Invade a portal of entry into various tissues. Viruses that infect the liver enter from the blood, leading to infection of Kupffer cells ( MФs) that line the liver sinusoids. Virions may be transcytosed across Kupffer and endothelial cells w/o replication to reach the underlying hepatic cells. Alternately, viruses may multiply in Kupffer and endothelial cells and then infect underlying hepatocytes. Either mechanism may induce inflammation and necrosis of liver tissue, a condition called HEPATITIS.
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(MIDII #131)
ORGAN INVASION => CNS, Connective Tissue, Skeletal & Cardiac Muscle |
Capillary endothelial cells in these tissues are usually not fenestrated; are backed w/ a dense basement membrane. In several well-defined parts of the brain, the capillary epithelium is fenestrated & the basement membrane is sparse. These highly vascularized sites include the choroid plexus. Some viruses (mumps virus, togaviruses) pass thru capillary endothelium & enter stroma of the choroid plexus, where they cross the epithelium into the CSF by transcytosis, or replication & directed release. Once in the CSF these viruses infect the ependymal cells lining the ventricles & invade the underlying brain tissue. Other virsues may directly infect or be transported across the capillary endothelium (picornaviruses & togaviruses). Some viruses cross the endothelium within infected monocytes or lymphocytes (HIV & measles virus). Increased local permeability of the capillary endothelium caused by certain hormones also permit viral entry into brain & spinal cord.
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(MIDII #132)
ORGAN INVASION => The Renal Glomerulus, Pancreas, Ileum & Colon |
To enter tissues that lack sinusoids, viruses must first adhere to endothelial cells lining capillaries or venules where blood flow is slowest and walls are thinnest. Once blood-borne viruses have adhered to the vessel wall, they can invade the renal glomerulus, pancreas, ileum or colon b/c the endothelial cells that make up the capillaries are fenestrated, permitting the virus or virus-infected cells to cross into the underlying tissues (poliovirus). Some viruses (herpes simplex, yellow fever, measles viruses) cross the endothelium while being carried by infected monocytes or lymphocytes via diapedesis.
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(MIDII #133)
ORGAN INVASION => The Fetus |
In a pregnant female, viremia may lead to infection of the developing fetus. The basement membrane is less well developed in the fetus. Infection can occur by invasion of the placental tissues followed by fetal tissue. Infected circulating cells (monocytes) may enter the fetal bloodstream directly. Virus may be transmitted to the baby during delivery or breast-feeding.
Examples: (a) Fetal death and abortion => smallpox virus, parvovirus; (b) Congenital defects => cytomegaloviruses, rubella; (c) Immunodeficiency => HIV 1; (d) Inapparent (lifelong carrier) => Lymphocytic choriomeningitis virus. |
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(MIDII #134)
TROPISM |
Most viruses do not infect all the cells of a host but are restricted to specific cell types of certain organs. The spectrum of tissues infected by virus is called TROPISM. ENTEROTROPIC virus replicates in the gut. A NEUROTROPIC virus replicates in cells of the nervous system. Some viruses are PANTROPIC, infecting and replicating in many cell types and tissues.
Tropism is governed by 4 parameters: (1) Distribution of receptors for entry (SUSCEPTIBILITY); (2) Requirement of the virus for differentially expressed intracellular gene products to complete the infection (PERMISSIVITY); (3) Even if a cell is permissive and susceptible, infection may not occur b/c virus is physically prevented from interacting w/the tissue (ACCESSIBILITY); (4) An infection may not occur even when tissue is accessible & cells are permissive and susceptible b/c of local intrinsic and innate immune defenses. |
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(MIDII #135)
Discuss CELLULAR PROTEASES and their role in viral infections. |
Many viruses require cellular proteases to cleave viral proteins for form the mature infectious virus particle. A cellular protease cleaves influenza virus HA precursor into 2 subunits so that fusion of the viral envelope and cell membrane can proceed. In mammals, the replication of flu virus is restricted to epithelial cells of the upper and lower respiratory tract. Tropism of this virus is influenced by limited expression of the protease that processes HA, called TRYPTASE CLARA, is secreted by non-ciliated CLARA cells of the bronchial and bronchiolar epithelia.
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(MIDII #136)
VIRAL VIRULENCE |
Viral virulence refers to the capacity of a virus to cause disease in an infected host. It is a quantitative statement of the degree or extent of pathogenesis. A virulent virus causes significant disease, whereas an avirulent virus causes no disease and an attenuated virus causes reduced disease.
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(MIDII #137)
How is viral virulence measured? |
(1)Determine Cx of virus that causes death or disease in 50% of infected animals: the 50% lethal dose (LD50), the 50% paralytic dose (PD50), or the 50% infectious dose (ID50), depending on the parameter measured. (2) Mean time to death or appearance of symptoms, and measurement of fever or weight loss. (3) Virus-induced tissue damage can be measured directly by examining histological sections or blood. (4) Safety of live attenuated poliovirus vaccine is det'd by assessing extent of pathological lesions in the CNS. (5) Reduction in blood Cx of CD4+ lymphocytes caused by HIV type 1 is a measurement of virulence. (6) Indirect measurements of virulence include assays for liver enzymes (alanine or aspartate amino-transferases) that are released into the blood as a result of virus-induced liver damage.
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(MIDII #138)
General Determinants of Virulence (1 of 4) => “Gene products that alter the ability of the virus to replicate” |
Genes that encode proteins affecting viral replication & virulence can be placed in 1 of 2 subclasses. (a) Viral mutants of subclass exhibit reduced or no replication in the animal host and in many cultured cell types. Reduced virulence results from failure to produce sufficient numbers of virus particles to cause disease, due to mutations in any viral gene. (b) Mutants of 2nd subclass exhibit impaired virulence in animals, but no replication defects in cells in culture.
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(MIDII #139)
General Determinants of Virulence (2 of 4) => “Gene products that modify the host's defense mechanisms” |
The study of viral virulence genes has ID'd a diverse array of viral proteins that sabotage the body's intrinsic defenses and innate & adaptive systems. Some of these viral proteins are called VIROKINES (secreted proteins that mimic cytokines, growth factors, or extra-cellular immune regulators) or VIROCEPTORS (homologs of host receptors). Mutations in genes encoding either class of protein affect virulence, but these genes are NOT required for growth in cell culture. Most virokines and viroreceptors have been discovered in the genomes of large DNA viruses.
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(MIDII #140)
Genetic Determinants of Virulence (3 of 4) => “Genes that enable the virus to spread in the host” |
Mutation of some viral genes disrupts spread from peripheral sites of inoculation to the organ where disease occurs. After intramuscular inoculation in mice, reovirus type 1 spreads to the CNS thru the blood while type 3 spreads by neural routes. The gene encoding the viral outer capsid protein S1 (which recognizes the cell receptor), determines route of spread.
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(MIDII #141)
Genetic Determinants of Virulence (4 of 4) => “Toxic viral proteins” |
Some viral gene products cause cell injury directly, and alterations in these genes reduces viral virulence. Evidence of intrinsic activity is obtained by adding purified proteins to cultured cells, or by synthesis of proteins from plasmids or viral vectors. The most convincing example of a viral protein w/intrinsic toxicity relevant to the viral disease is the NSP4 protein of rotaviruses which causes gastroenteritis and diarrhea. NSP4 is a non-structural glycoprotein, participates in formation of a transient envelope as particles bud into the ER. When protein is fed to young mice it causes diarrhea by potentiating chloride secretion. Acts as a viral enterotoxin and triggers a signal transduction pathway in the intestinal mucosa.
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(MIDII #142)
Injury Caused By Viral Infections => Do the clinical symptoms of viral disease result from the host response to infection or from the virus itself? |
Clinical symptoms of viral disease in the host (fever, tissue damage, aches, pains, nausea) result primarily from the host response to infection which is initiated by cell injury caused by viral replication. Cell injury can result from the direct effects of viral replication on the cell, or from the consequences of the host's intrinsic, innate, and adaptive immune responses.
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(MIDII #143)
Injury Caused By Viral Infections => Direct Effects of Primary Infection: Cytopathic Effect |
(1)Infection of cultured cells can result in visible changes in the cells called CYTOPATHIC EFFECT. Direct alteration of the cell can clearly account for some of the damage observed during infections in an animal host. Poliovirus induces cytopathic effects in cultured neuronal cells. Virus-induced killing of neurons in the CNS can account for paralytic symptoms characteristic of poliomylitis. Apoptosis of virally infected cells leads to visible cell damage. (2) Viral infection may also cause cessation of essential host processes such as translation, DNA & RNA synthesis, & vesicular transport; ↑ permeability of cell membranes. Lysosomal contents diffuse into the cytoplasm resulting in autolytic digestion of the cell. (3) Host genome can be directly damaged by viral infection. Retrovirus replication cycle requires insertion of a proviral DNA copy into random locations in the cell genome. Insertion affects expression or integrity of a cellular gene, a process known as INSERTIONAL MUTAGENESIS.
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(MIDII #144)
How is immunopathology “too much of a good thing”? |
Most symptoms and many diseases caused by viral infection are a consequence of the immune response. Damage caused by the immune system is called immunopathology – price paid by the host to eliminate a viral infection. For non-cytolytic viruses the immune response is the sole cause of disease.
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(MIDII #145)
Immunopathological Lesions => Lesions caused by cytotoxic T lymphocytes (CTLs) |
Examples: (1) Myocarditis (inflammation of the heart muscle) caused by coxsackievirus B infection of mice requires presence of CTLs. Perforin is a major determinant of endocarditis. Mice lacking the perforin gene develop a mild form of heart disease but are still able to clear the infection. (2) The acute and fatal respiratory disease caused by hantaviruses is characterized by prominent infiltration of CTLs into the lung.
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(MIDII #146)
Immunopathological Lesions => Lesions caused by CD4+ T cells |
CD4+ T cells elaborate more cytokines than CTLs and recruit and activate many non-specific effector cells => Delayed type hypersensitivity responses. Most recruited cells are PMNs and mononuclear cells which are protective and cause tissue damage. Immunopathology results from release of proteolytic enzymes, reactive free radicals such as H2O2 and nitric oxide (NO), and cytokines (TNF-alpha).
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(MIDII #147)
Immunopathological Lesions => Lesions Caused by CD4+ Th1 Cells: Herpes Stromal Keratitis |
(MIDII #147)
Immunopathological Lesions => Lesions Caused by CD4+ Th1 Cells: Herpes Stromal Keratitis |
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(MIDII #148)
Immunopathological Lesions => Lesions Caused by CD4+ Th2 Cells: Respiratory Syncytial Virus |
RSV may be mediated by CD4+ Th2 cells. Non-cytopathic virus. Impt cause of lower respiratory tract disease in infants and the elderly. Lesions are minor in immunosuppressed mice, but become severe after transfer of viral antigen-specific T cells, particularly CD4+ Th2 cells. Lesions in the respiratory tract contain many eos, which may be responsible for pathology. Th2 cells secrete cytokines that recruit eos.
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(MIDII #149)
Immunopathologic Lesions => Lesions Caused By B Cells: Viral-Antibody Complexes |
Virus-Ab complexes accumulate in high Cx's when lots of viral replication occurs at sites inaccessible to the immune system or continues in the presence of an inadequate immune response. These complexes aren't efficiently cleared by the reticuloendothelial system and continue to circulate in the blood. They become deposited in the smallest capillaries and cause lesions that are exacerbated when complement is activated. Deposition of these immune complexes in blood vessels, kidney and brain may result in vasculitis, glomerulonephritis, and mental confusion, respectively.
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(MIDII #150)
How can Abs enhance viral infection in Dengue Hemorrhagic Fever? |
Disease is transmitted by mosquitoes. Endemic in the Caribbean, Central & South America, Africa & Southeast Asia where billions of ppl are at risk. Primary infection is usually asymptomatic, may result in a self-limiting acute febrile illness with severe headache, back & limb pain, and a rash. There are 4 viral serotypes and Abs to any one of these does not protect against infection by the other. After infection by another serotype of dengue virus, non-protective Abs bind virus particles and facilitate uptake into normally non-susceptible peripheral blood monocytes carrying Fc-receptors. The infected monocytes produce pro-inflammatory cytokines which stimulate T cells to produce more cytokines, resulting in high Cx's of cytokines and chemical mediators that trigger plasma leakage & hemorrhage characteristic of dengue hemorrhagic fever. Lots of internal bleeding => fatal dengue shock syndrome can result. Dengue hemorrhagic fever occurs in 1 in 14,000 primary infections. After infection w/dengue virus of another serotype, incidence of hemorrhagic fever increases to 1 in 90, and shock syndrome is seen in as many as 1 in 50.
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(MIDII #151)
Discuss Viral Infection Injury Mediated By Free Radicals. |
NO is produced in virus-infected tissues during inflammation as part of the innate immune response. Inhibits replication of viruses in cultured cells and animal models. Low Cx's of NO have a protective effect. High Cx's or prolonged production can contribute to tissue damage. Treating infected animals w/ inhibitors of NO synthase prevents tissue damage. NO is relatively inert but rapidly reacts with O2 to form peroxynitrite (ONOO-) which is much more reactive and may be responsible for cytotoxic effects on cells.
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(MIDII #152)
What is the basis for establishing a diagnosis of HIV in established (non-acute) HIV infection? |
Initial test: ELISA that can be HIV-1 specific or may screen for HIV-1 and HIV-2 (frequently seen in blood banks). A positive ELISA Ab must be confirmed by a 2nd test, typically a western blot which detects serum Abs to specific HIV proteins (antigens) that are separated on a gel. Recently, rapid HIV antibody tests that can give results in 30 minutes to a few hours have been approved by the FDA. [Remember, an HIV test cannot be legally performed on any person w/o written permission. Pre-test and post-test counseling must be provided to all individuals willing to be tested.]
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(MIDII #153)
What testing should be done on a patient presenting with acute (or primary) HIV infection? |
Patient may present to a health care provider prior to full seroconversion. HIV Ab should be done but the ELISA may be negative or the ELISA may be positive with a negative or indeterminate Western blot. A plasma HIV-1 RNA test should be done as the viral load (RNA concentration in plasma) is typically very high during the acute phase of HIV infection. A follow-up Ab test should be done to confirm that full seroconversion (positive ELISA and Western blot) has occurred.
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(MIDII #154)
Discuss the structure of the HIV virus. |
HIV is a retrovirus. It is a single-stranded RNA virus w/an icosahedral nucleocapsid and a lipid envelope. Virion has 2 identical copies of RNA and carries a unique viral enzyme, the reverse transcriptase. Virus replication scheme is as follows: (1) Binding & infection; (2) Reverse transcription & integration of viral DNA into the host genome; (3) Transcription & translation of HIV proteins; (4) Modification and assembly; (5) Budding and final assembly.
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(MIDII #155)
The HIV genome is 10 kB in length and consists of 3 major (Gag, Pol, Env) and 6 accessory genes. Discuss these: |
(1) Gag codes for internal structural proteins. (2) Pol codes for the viruses major enzymes – reverse transcriptase, protease and integrase. (3) Env codes for the gp120 envelope glycoprotein and the gp41 transmembrane protein, which mediate attachment and entry of the virus into the host cell. (4) Tat, Rev, Nef, Vif, Vpr and Vpu are accessory proteins which are involved in amplification of virus replication, infectivity, and pathogenesis.
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(MIDII #156)
What are the pathogenic steps for primary (acute) HIV infection? |
(1)Viruses must interact with Dcs – first encounter the virus has following deposition on the mucosal surface. Primary infection is w/R5 (MΦ-[M]-tropic) viral strains. DC-SIGN is an impt HIV receptor on the surface of DC's. (2) Virus is delivered to lymph nodes where very active replication takes place. DC's act as transporters of HIV and do not primarily support HIV replication. (3) High levels of viremia and viral dissemination occur. (4) Downregulation of virus replication by immune response occurs in the absence of treatment. Mediated by CD8+ cytotoxic T cells. Neutralizing Abs are formed but virus titers fall before these Abs are fully developed. (5) A viral 'set point' is reached after approximately 6 months. Viral set point is predictive of the rate of subsequent disease progression.
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(MIDII #157)
Does HIV viral replication occur during the long latency period between the time of infection and the development of clinical AIDS? How is clinical AIDS defined? What are rapid progressors and long-term non-progressors? |
Active viral replication is present throughout the course of disease despite clinical latency period. Clinical AIDS is defined as a CD4+ count <200/mm3, or the development of an HIV-related opportunistic infection or malignancy). Clinical illness develops as the CD4 count falls below 200/mm^3. Risk is progressive as CD4 count falls below this level. Avg time from infection to clinical AIDS is 8-10 yrs. There are rapid progressors who develop AIDS within 2 yrs and long-term non-progressors (LTNPs) who maintain normal CD4 counts and very low viral loads in the absence of treatment for >10-15 yrs. These form a very small percentage of overall HIV infected population but provide insights into how an HIV vaccine might be created.
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(MIDII #158)
HIV virus is measured in peripheral blood. Are there reservoirs of infection outside the blood compartment? |
Yes! Include lymphoreticular tissues (the major “factory” of HIV in lymph nodes, spleen & GI tract), the CNS, and the genital tract.
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(MIDII #159)
Does HIV exist in the host as one species or multiple quasispecies? |
The virus exists as multiple quasispecies or swarms of viruses. Mixtures of viruses w/differential phenotypic & genotypic characteristics may coexist in the same body compartment or across body compartments. Viruses with different cell tropisms or drug resistance patterns may (and do) coexist in an infected person.
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(MIDII #160)
How many virions are produced and destroyed each day in the life of an infected individual? What is the half life of HIV in plasma? |
10 x 10^9 virions are produced and destroyed each day in the life of an infected individual. Turnover of HIV in the body is enormous with the half life in plasma estimated at <6 hrs and as short as 30 min. Outcome of infection is a balance between virulence of the pathogen and host factors. Strength of innate and acquired immune responses (especially CD8+ cytotoxic T cells), chemokine receptor status and HLA type of the infected person are impt codeterminants of the outcome.
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(MIDII #161)
Gastrointestinal viruses are major causes of morbidity and mortality throughout the world. All of these viruses enter through the GI tract but the diseases associated with them are not confined to the GI tract. Among enteroviruses, rotaviruses and calciviruses, which family of viruses produces a number of different disease syndromes and which have infections largely confined to GI illness? |
Enteroviruses produce a variety of disease syndromes. Rotaviruses and calciviruses are mainly confined to GI illness.
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(MIDII #162)
Discuss Enteroviruses as a family. |
Members of the Picornaviridae family of very small RNA viruses which also includes aphthoviruses, cardioviruses and rhinoviruses. Enteroviruses have been divided into subgroups consisting of polioviruses, coxsacieviruses, echoviruses, and the so-called 'newer enteroviruses.' They are small, non-enveloped single stranded positive sense RNA viruses.
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(MIDII #163)
Discuss molecular biology and pathogenesis of infection by enteroviruses. |
Enter the body thru GI tract, usually from fecally contaminated material. Virus multiplies in submucosal lymphatic tissues of the gut and passes to regional lymph nodes and the reticuloendothelial system. Usually contained in the immune system resulting in subclinical infection. However, sometimes heavy sustained replication occurs and the virus is shed into the bloodstream causing disease at many distant sites. Virus penetrates host cells, uncoats and releases its RNA into the cytoplasm within minutes. Inside the cell, RNA is translated into a polyprotein which is subsequently cleaved to form: (a) 4 viral capsid proteins which make up the icosohedral covering of the virus protecting the viral RNA and allowing the virus to attach to its host cell. (b) 8 non-structural proteins whose functions include: RNA replication, protease activity, and inhibition of host cell protein synthesis.
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(MIDII #164)
At what point in enterovirus infection are inflammatory or necrotic lesions noted in body tissues? Are such lesions found in the gut or lymphoreticular system where the virus originally replicates? |
While virus originally replicates in gut or lymphoreticular system, few inflammatory or necrotic lesions are noted in these tissues. However, targets of the viremic stage usually show significant inflammation and necrosis which correlates with the titer of virus present. Produces much of the morbidity associated with the infection.
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(MIDII #165)
POLIOVIRUS => Discuss Pathogenesis of the Virus. |
Polioviruses cause poliomyelitis, a systemic infectious disease of varying severity. Usually affects the CNS and can result in paralysis. Humans are the only natural host and reservoir of polioviruses. Discuss the characteristic histopathology of poliovirus, with regard to the distribution of lesions.
Polio enters thru the gut, replicates in the submucosal lymphoid tissue, & spreads to the reticuloendothelial system. In susceptible hosts, virus spreads thru blood to CNS where it causes extensive necrosis of neurons in the gray matter of the spinal cord & brain. Polio primarily infects autonomic and motor neurons. Destruction of these neurons is accompanied by an inflammatory infiltrate of PMNs, lymphocytes and MΦs. Main sites of attack are the gray matter of the anterior horn of the spinal cord and motor nuclei of the pons and medulla. |
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(MIDII #166)
Discuss the Epidemiology of Poliomyelitis. |
Before 1900 polioviruses were ubiquitous, resulted in mostly inapparent early childhood infection. With rising hygienic standards, infection was delayed until later in childhood, creating a pool of susceptible hosts and conditions for an epidemic. Increase in paralytic disease in the 1950s was due to the fact that (while infected infants are protected by maternal Ab) older children have no natural immunity. Introduction of the 1st polio vaccine in 1955 led to dramatic reductions in polio cases in the US and other developed countries. Last case of WT polio in the US occurred in 1979. Polio has been eradicated from the western hemisphere and Europe. Polio infections still occur in developing countries.
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(MIDII #167)
Clinical Features of Polio Infection |
The incubation period of polio (from presumed contact until onset of the prodrome) is 9-12 days. Manifestations of infection by poliovirus range from inapparent illness to severe paralysis and death. At least 95% of infections are asymptomatic. Symptomatic disease can take a number of increasingly severe forms, including: (1) Abortive poliomyelitis, (2) Nonparalytic poliomyelitis, (3) Spinal paralytic poliomyelitis, (4) Bulbar paralytic poliomyelitis, (5) Polioencephalitis.
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(MIDII #168)
Clinical Features of Polio Infection => Abortive Poliomyelitis and Nonparalytic Poliomyelitis |
ABORTIVE POLIOMYELITIS: Occurs in 4-8% of infections. Characterized by fever, headache, sore throat, listlessness, anorexia, vomiting, and abdominal pain. Neurological exam is normal and illness lasts only a few days.
NONPARALYTIC POLIOMYELITIS: Differs from abortive polio b/c there are signs of meningeal irritation. Systemic symptoms are generally more severe. Clinically indistinguishable from other enterovirus-associated meningitides and full recovery is the norm. |
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(MIDII #169)
Clinical Features of Polio Infection => Spinal Paralytic Poliomyelitis |
SPINAL PARALYTIC POLIOMYELITIS occurs in 0.1% of polio infections. In kids there is a biphasic course with 'minor' and 'major' illnesses. The minor illness corresponds with viremia and symptoms mimic those of abortive polio. Patient recovers after 1-3 days of mild illness, remains well for 2-5 days but then abruptly becomes ill w/headache, fever, vomiting, & neck stiffness. Characteristic of onset of this major illness is muscle pain that is relieved by motion. This phase lasts 1-2 days before frank weakness and flaccid paralysis ensues. Severity is variable, ranging from a single portion of one muscle to quadriplegia. Paralysis is asymmetric, w/proximal muscles more affected than distal muscles. Continues to evolve until fever dissipates in 2-3 days. Sensory loss is very rare in polio and suggests an alternate diagnosis.
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(MIDII #170)
Clinical Features of Polio Infection => Bulbar Paralytic Poliomyelitis |
BULBAR PARALYTIC POLIOMYELITIS is characterized by paralysis of the muscles innervated by the cranial nerves. Results in dysphagia, nasal speech, and dyspnea with cranial nerves 9 and 10 (vagus) most commonly affected. Involvement of vasomotor and respiratory centers is less common, but results in a rapid pulse, hypoxia, and elevated BP followed by a circulatory collapse which can result in death.
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(MIDII #171)
Clinical Features of Polio Infection => Polioencephalitis |
POLIOENCEPHALITIS is manifested by confusion and changes in mental status. It is uncommon and occurs primarily in infants. Paralysis, if it occurs, is spastic, suggesting upper motor neuron disease.
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(MIDII #172)
How is poliovirus infection diagnosed? |
Poliovirus can be diagnosed from throat secretions in the 1st wk of illness, and from feces for several wks. Unlike other enteroviruses, RARELY isolated from the CSF. Diagnosis can also be made by testing paired acute and convalescent sera for a rise in Ab titer.
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(MIDII #173)
Discuss prevention of poliovirus infection by vaccines. |
Poliovirus vaccines have been used successfully for over 30 yrs. Wiped out WT poliovirus infections from the western hemisphere. 2 vaccine formulations are currently available: (1) the oral polio vaccine (OPV) and (2) the inactivated polio vaccine (IPV). OPV is a live attenuated vaccine and was the mainstay of vaccination compaigns worldwide for many yrs. Given orally, more immunogenic than the original IPV, and since it is excreted in the feces of vaccinated individuals, it allows for spread of vaccine virus to unimmunized individuals. As cases of naturally occuring poliovirus infection fell in the developed world, the risk of the very rare (but real) paralytic disease resulting from the OPV virus itself exceeded that of naturally occurring polio and the US has since recommended that we only use IPV. The original Salk IPV has been modified to make it more immunogenic (at least equal to OPV). Excellent safety record and can be safely given to immunocompromised individuals as it contains no live virus.
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(MIDII #174)
Central Nervous System Infections Caused by Enteroviruses: => Aseptic Meningitis |
Aseptic meningitis is characterized by signs & symptoms of meningeal irritation in the absence of bacteria or fungi. Most community acquired cases of aseptic meningitis are caused by viruses. 90% are caused by group B coxsackieviruses & echoviruses. Infants less than 3 months of age have the highest rates of clinically recognized aseptic meningitis. In older kids and adults severity of disease varies widely. Typical patient has prodrome of fever & chills followed by headache, stiff neck, & symptoms of an upper RT infection. These infections are usually self-limited & uncomplicated. Dx depends on examination of CSF which shows clear fluid with 10-500 white cells. White cells may be predominantly PMNs initially but the differential will shift to a lymphocyte predominance over 1st 1-2 days of illness. CSF glucose and protein Cx's are normal or very slightly elevated. Enteroviruses can be detected in the CSF by PCR or cell culture. Differential Dx includes partially treated bacterial meningitis, other viral meningitis (arbovirus, LCMV, HIV-associated meningitis), Lyme disease, leptospirosis.
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(MIDII #175)
CNS infections caused by Enteroviruses => Aseptic Meningtis How do we treat aseptic meningitis caused by enteroviruses? |
Treatment consists of asymptomatic relief. Pleconaril, an orally administered picornaviral capsid-stabilizing drug, decreases the duration of symptoms but has been disappointing in clinical trials of severely ill patients.
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(MIDII #176)
CNS infections caused by Enteroviruses => ENCEPHALITIS |
Enterovirus caused encephalitis is a rare manifestation of echo virus and coxsackievirus CNS infection. Enteroviruses (including polio) account for 11-22% of viral encephalitis cases. Kids and young adults are most commonly affected w/clinical manifestations ranging from lethargy and drowsiness to seizures and coma. The prognosis (except in infants) is excellent.
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(MIDII #177)
CNS infections caused by Enteroviruses => Chronic Meningoencephalitis |
Seen in pts w/acquired or hereditary defects in B-lymphocyte function. Mostly children with X-linked agammaglobulinemia. Mostly caused by echoviruses. Nervous system manifestations range from mild nuchal rigidity & headache to seizures & ataxia. Enterovirus can be recovered from the CSF for months to years. In many (if not most) affected persons the disease ends in death. Prophylactic use of intravenous immune globulin is currently used to prevent enteroviral infection in pts w/B cell defects. Used less successfully to treat those w/chronic meningoencephalitis.
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(MIDII #178)
CNS infections caused by Enteroviruses => Paralysis |
Paralysis is associated w/infection by coxsackie and enterovirus infection. Coxsackievirus A7 and enterovirus 71 have been associated w/outbreaks of flaccid paralysis. Paralytic disease caused by nonpolio enteroviruses is less severe than poliovirus associated paralysis. Paresis (partial or incomplete paralysis) is not permanent. Guillain-Barre syndrome, transverse myelitis, and Reye's syndrome have all been associated w/enteroviruses.
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(MIDII #179)
Enterovirus associated exanthems or rashes => MORBILLIFORM EXANTHEMS |
[NOTE: Exanthems or Rashes are common features of enterovirus infections. Note that these rashes can take many forms and (with the exception of hand-foot-and-mouth disease) are not distinctive enough o make a definitive diagnosis.]
Morbilliform Exanthems are fine, erythematous, maculopapular (both flat and raised) rashes that are common manifestations of echovirus infections especially during summer outbreaks. Most common serotype associated w/this rash is echovirus 9. Rash appears simultaneously w/fever and starts on the face spreading to the chest and extremities. |
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(MIDII #180)
Enterovirus associated exanthems or rashes => ROSEOLIFORM EXANTHEMS |
Discrete, nonpruritic (not itchy), salmon-pink macules and papules which appear on the face and upper chest. Usually associated with a prodrome of fever and pharyngitis. Rash doesn't appear until after the patient has defervesced. Generally lasts 1-5 days. Infections are quite contagious, usually occur in young children. Echovirus 16 is most commonly associated w/this syndrome.
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(MIDII #181)
Enterovirus associated exanthems or rashes => Hand-Foot-and-Mouth Disease |
Distinctive vesicular eruption caused by coxsackie virus A16 or enterovirus 71. Common in children under age 10. Characterized by fever and vesicles in the oral cavity, hands and feet. Palms and soles may be affected. Lesions are tender – mixed papules and clear vesicles with surrounding erythema. The Differential Dx is chickenpox. However, while patients with HFM disease invariably have oral mucosal lesions, oral lesions are less common in chickenpox. Pts with chickenpox appear more ill than those with HFM disease. It can be tough to tell them apart, however, and these may account for 'repeat' cases of chickenpox.
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(MIDII #182)
Enterovirus associated exanthems or rashes => Generalized vesicular eruptions |
Coxsackievirus A9 and echovirus 11 cause generalized vesicular eruptions. Similar to the lesions of HFM disease but occur in crops on the head, trunk, and extremities. Unlike chickenpox, they do not evolve into pustules and scabs.
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(MIDII #183)
Enterovirus associated exanthems or rashes => Herpangina |
Well-characterized vesicular rash involving the pharynx and soft palate accompanied by fever, sore throat, and pain on swallowing. Usually seen in summer outbreaks. Group A coxsackieviruses are commonly associated. Illness begins suddenly w/fever, vomiting, myalgia and headache which resolve quickly. Sore throat and pain on swallowing precede development of oral lesions. Prompt recovery over a week occurs in all cases.
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(MIDII #184)
Enterovirus Associated Respiratory Disease => COLDS |
Many enteroviruses cause undifferentiated febrile illness with sore throat, cough, and corya (runny nose). Account for a large number of viruses recovered from children with summer colds. Coxsackieviruses A21 and A24 produce common cold symptoms indistinguishable from rhinovirus infections except for a higher percentage of fever. Echovirus 11 is the most common echovirus cause of cold-like syndromes.
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(MIDII #185)
Enterovirus Associated Respiratory Diseases => EPIDEMIC PLEURODYNIA |
Acute disease characterized by fever and sharp, spasmodic pain in the chest or upper abdomen. Group B coxsackieviruses are the most common etiologic agents, can cause major epidemics. Pleurodynia is a disease of muscle (not pleura) and tenderness mimicking the pain of infection can be elicited by placing pressure on the affected muscle. Characterized by abrupt onset of spasmodic pain with fever which peak one hr after each paroxysm and subside as pain decreases. Most patients are ill for 4-6 days and adults are more severely affected than children. Disease may relapse and can occur over a several month period, but all patients eventually recover completely.
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(MIDII #186)
Discuss Enterovirus Associated Myopericarditis => Pathogenesis |
Myopericarditis is inflammation of the myocardium and pericardium. Enteroviruses are the most common viral etiologic agents accounting for 50% of all cases of acute myopericarditis. All group B coxsackieviruses, group A types 4 and 16 and echoviruses types 9 and 22 have been definitively linked to myopericarditis. Virus reaches the heart during the viremia that follows replication in the retinculoendothelial system. Virus replication occurs in the myofibers and results in scattered myofiber necrosis followed by focal inflammatory infiltrates. Healing is accompanied by a variable degree of interstitial fibrosis and evidence of myocyte loss.
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(MIDII #187)
Discuss Enterovirus Associated Myopericarditis => Clinical Manifestations and Sequelae |
Variable clinical manifestations. Occurs in all ages. Special predilection for physically active adolescents and young adults. Incidence in males is 2x that in females. In >60% of cases, upper respiratory illness precedes onset of cardiac symptoms by 7-14 days. Cardiac involvement is heralded by dyspnea, chest pain, fever & malaise. Chest pain is in the precordial area, usually dull and relieved by sitting up and forward. EKG abnormalities are almost always present. Echocardiograms may show dilatation and dysfunction of the heart muscles. Serum levels of myocardium enzymes are elevated. Frank congestive heart failure is present in 20% of cases. Chronic dilated cardiomyopathy leading to chronic congestive heart failure is the most dreaded complication of enteroviral myopericarditis. 1/3 of pts will have some permanent sequelae including EKG changes, cardiomegaly & chronic constrictive pericarditis. Management is mainly supportive. IV IG (pooled immunoglobulin from multiple blood donors) has shown some value.
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(MIDII #188)
Discuss Enteroviral Infection of Newborn Infants => How do they catch infection? |
Neonates are uniquely susceptible to enterovirus infections. Group B coxsackieviruses serotypes 2-5 and echovirus 11 are the most common culprits. Most neonatal enteroviral infections are acquired directly from the mother but nosocomial outbreaks have been reported. Most neonates are infected in the perinatal period. 60-70% of women transmitting the infection will have fever in the wk prior to delivery. Once newborn is infected, enterovirus spreads systemically through the bloodstream. Has particular tropism for the heart & liver. Neonates can form neutralizing Ab to enteroviral infections but lack the MΦ activity needed to control infection completely.
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(MIDII #189)
Discuss the Clinical Manifestations of Enteroviral Infection of Neonates. |
Symptoms develop between 3-7 days of life. Generally mild and nonspecific. 1/3 have a biphasic illness w/ a period of 1-7 days of well-being between initial symptoms and more serious manifestations. Generalized enterovirus disease in the newborn usually occurs in 1 of 2 characteristic clinical syndromes: myocarditis or hepatitis. Myocarditis, which is often accompanied by encephalitis, is usually caused by Group B coxsackieviruses. Fulminant hepatitis is characterized by hypotension, profuse bleeding, jaundice, and multiple organ failure and results from echovirus 11 infection. Dx of neonatal enterovirus infection is rapidly made w/PCR or viral culture. Virus can be detected in urine, feces, blood, CSF, and oropharyngeal secretions. Management is supportive. IVIG may be considered (as may pleconaril but results with this drug have been disappointing to date.)
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(MIDII #190)
Discuss Acute Hemorrhagic Conjunctivitis associated with Enterovirus 70 Infection. |
Contagious ocular infection characterized by pain, swelling of the eyelids, and subconjunctival hemorrhage that generally resolves spontaneously within a wk. Enterovirus 70 causes this infection. Has caused epidemics in Africa, Asia, and Europe. Acute hemorrhagic conjunctivitis is spread from fingers directly to the eye. Highly contagious and spreads rapidly. Begins abruptly with burning, pain, photophobia and watery discharge in one eye followed a few hours later by symptoms in the other eye. Conjunctival hemorrhage can be pinpoint or occupy the entire conjunctiva. Most cases resolve spontaneously but a few may be followed by motor paralysis mimicking poliomyelitis.
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(MIDII #191)
ROTAVIRUSES => General Description |
Rotaviruses are large, non-enveloped RNA viruses that are responsible for 10-20% of all diarrhea related deaths in children worldwide and account for up to 120,000 hospitalizations in the US each year. They are members of the Reovirus family. Wheel-like appearance. Genome is segmented dsRNA. Segmented genome allows for reassortment of strands when 2 different strains coinfect a single host cell. Allows the virus to adapt to combat host defenses, although major antigenic shifts like those in influenza A don't occur. Since the genome RNA is double-stranded it can't function directly as mRNA so these viruses package their own RNA polymerase to make mRNA.
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(MIDII #192)
ROTAVIRUSES => Describe the replicative cycle of rotaviruses. |
(1) Viral entry via phagosome; (2) Release from phagosome; (3) Uncoating, release of RNA, and transcription into mRNA; (4) Production of viral proteins; (5) Viral RNA synthesis; (6) Movement of viral proteins; (7) Movement of core to ER; (8) Assembly of viral particle; (9) Release of viral particle.
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(MIDII #193)
Discuss Pathogenesis of Infection with Rotaviruses. |
There are 7 (A-G) antigenic groups of Rotaviruses. Only groups A-C cause disease in humans with group A viruses responsible for most human disease worldwide. Rotaviruses are spread via the oral-fecal route. Since they lack an envelope they are quite resistant to gastric acid (and disinfectants). Highly infectious, infectious dose as low as 1pfu. Replicate in mature villus epithelial cells of the small intestine. Infection of the villus epithelium results in loss of those cells, resulting in decrease in absorptive area of the intestine. Can result in lactase deficiency, a common sequela of viral and bacterial gastroenteritis. Cause vomiting and diarrhea. NSP4 protein of rotavirus acts in a toxinlike manner to promote Ca2+ ion influx into enterocytes, release of neuronal activators, and a neuronal alteration in water absorption.
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(MIDII #194)
Discuss the Epidemiology of Infection with Rotaviruses. |
Occur worldwide. Almost everyone over age 2 has been infected w/at least 1 strain of rotavirus. Infections in temperate climates are seasonal, occurring over a 3-4 month period in the winter. In North America infections begin in late autumn in Mexico and spread north and east ending up in eastern Canada by the spring. No cases in the summer months.
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(MIDII #195)
ROTAVIRUSES => Clinical Features |
Range from asymptomatic to severe gastroenteritis. First infection is the most severe. Rotavirus infection involves both vomiting and diarrhea accompanied in severe cases by nausea and a high fever. Diarrhea is watery w/o mucous or blood. Fecal leukocytes might be present in severe rotavirus infections (not in viral diarrheas). Dehydration and electrolyte imbalance are the most common reasons for hospitalization and death from rotavirus infection.
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(MIDII #196)
ROTAVIRUSES => Diagnosis and Treatment |
(Dx) Diagnosis can be suspected clinically in a febrile young infant with both vomiting and diarrhea in the winter. Most clinical labs use ELISAs to detect rotavirus antigens in stool samples or PCR. Electron microscopy of stool will show characteristic wheel-shaped viral particles (but this doesn't happen in most hospital labs). (Rx) Treatment is supportive w/replacement of fluid and electrolytes either orally or IV. Early feeding is encouraged, promotes enterocyte regeneration and decreases intestinal permeability. Antidiarrheal medications are not recommended (body is trying to get rid of the virus for a reason and we don't want to interfere with that attempt).
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(MIDII #197)
ROTAVIRUSES => Prevention |
Good hygiene (washing hands!!) and chemical disinfection are the best ways to prevent rotavirus spread in communities and households. Almost everyone is infected and mounts an immune response to infection by age 2, but immunity to rotavirus is NOT complete and infections do occur in older children and adults. Usually these infections are milder than in young infants. A vaccine called Rotashield was licensed for use in the US in 1998 and was highly effective but after 10 months on the market there were 10 reported cases of intussusception (telescoping of the bowel on itself – a nasty complication that requires surgical repair and can be fatal) were reported in young vaccinated infants. In July of 1999 the FDA halted vaccination and the vaccine was pulled from the market. Few children die from Rotavirus infection in the US, so this is reasonable here, but in the developing world death rates are much higher to the decision to pull the vaccine is more controversial.
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(MIDII #198)
CALICIVIRUSES (“The Love Boat Bugs”) => General Description |
Single stranded, positive sense RNA viruses that are responsible for many outbreaks of gastrointestinal illness across the world. They get their name from the 'cuplike' indentations on their surfaces. Caliciviruses are simple, non-enveloped viruses whose genome encodes 4 polypeptide products: (1) HELICASE which unwinds double helical regions in RNA during recombination, replication, transcription and splicing. (2) PROTEASE which is responsible for cleaving the single polypeptide into its functional parts. (3) RNA POLYMERASE which is responsible for replicating RNA. (4) CAPSIDE which covers the RNA genome.
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(MIDII #199)
CALICIVIRUSES => Pathogenesis |
Caliciviruses can't grow in cell culture. Spread thru oral-fecal route. Since they are non-enveloped they can survive gastric acid and pass into the small bowel where they cause disease. Acute calicivirus infection results in a reversible lesion in the jejunum characterized by blunting of the villi which appears within 24 hrs of infection. Mucosa remains intact. PMNs are seen in the lamina propria. Diarrhea is associated w/ transient malabsorption of D-xylose and fat; and decreased activity of brush-border enzymes. Infection is NOT associated w/ detectable toxin production. Exact mechanism behind diarrhea & vomiting is not known. Virus shedding in stool is highest in the first 24-48 hrs after illness; rarely detected beyond 72 hrs after illness onset. Patients are most infectious while symptomatic.
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(MIDII #200)
CALICIVIRUSES => Epidemiology |
Caliciviruses are widespread and common. Disease can occur throughout the year and affects all age groups. Almost any type of food that has contact with contaminated water (shellfish) may serve as a vehicle for outbreaks of calicivirus gastroenteritis. Contaminated drinking water and swimming pools and lakes in which infected ppl have swum can be vehicles for outbreaks. Viruses are hardy, can withstand chlorination, heat inactivation (cooking doesn't eliminate risk of transmission). Responsible for recent large outbreaks of diarrheal illness reported on cruise ships.
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(MIDII #201)
CALICIVIRUSES => Clinical Manifestations |
Caliciviruses were first ID'd in point-source outbreaks of gastroenteritis and remain impt causes of such outbreaks. Features: short-lived illness (2-3 days duration), with vomiting as predominant symptom, incubation period of 24-48 hrs, high secondary attack rates (spread well!). Both vomiting and diarrhea generally occur; myalgias, malaise, and fever are common. Disease manifestations generally last 48-72 hrs and remit without sequelae.
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(MIDII #202)
CALICIVIRUSES => Diagnosis, Treatment and Prevention |
(Dx) Diagnosis can be suspected on clinical and epidemiological grounds and by the absence of any other pathogen. Lab tests are NOT useful. Electron microscopy of stool samples can reveal characteristic virus particles but is not used outside of research setting. An ELISA test for calicivirus antigens is in the works but is not yet widely available. (Rx and Prevention): Treatment is supportive only. Oral fluid replacement is all that is necessary. Some will need IV rehydration. No vaccine is available. Prevention is primarily through judicious food and water handling.
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(MIDII #203)
INFLUENZA => General Description |
Influenza viruses cause acute, self-limited febrile illnesses most often in the winter months. Belong to orthomyxoviridae family. 3 types: flu A, B, and C. Influenza A and B cause human disease w/significant morbidity & mortality. Flu C infections are generally subclinical. Influenza viruses are enveloped viruses w/segmented, neg sense RNA genomes. Flu A and B have 8 segments in their genome while Flu C has 7 (lacks a neuraminidase protein).
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(MIDII #204)
INFLUENZA => Discuss the important Viral Proteins |
(1)PB I, PB2, and PA => viral polymerase proteins, allow the virus to replicate its RNA. (2) NA (neuraminidase protein) => protrudes thru the viral envelope, catalyzes removal of sialic acid residues, allowing the virus to escape from its host cell and move thru mucus. (3) HA (hemagglutinin protein) => protrudes thru the viral envelope, binds to sialic acid residues, major attachment protein for the virus. Mediates fusion between the viral envelope and the endosome, which is how the virus gains entry into cells. NA and HA are the 2 major antigenic proteins against which neutralizing Abs are made to influenza. (4) NP is the nucleocapsid protein, covers viral genome. (5) M protein(s) located inside the viral envelope. M1 is found in Flu A&B and provides stability to the virion. M2 (only in flu A) acts as an ion channel within the endosome. (6) NS => nonstructural proteins, function is not clear.
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(MIDII #205)
INFLUENZA => Immune Evasion Influenza is constantly changing in order to avoid immune detection. Accounts for annual flu seasons and periodic pandemics. Mechanisms that the virus uses to change its antigenic sites are called DRIFT and SHIFT. Discuss and distinguish between ANTIGENIC DRIFT and ANTIGENIC SHIFT. |
(1: Antigenic Drift): HA &NA proteins of influenza viruses are major sites for Ab recognition on the virus. To help the virus evade Ab detection, the RNA segments that encode NA & HA mutate, keeping their functions intact but making them less well recognized by Abs. Ongoing mutation = antigenic drift: occurs in influenza A & B. Drift is responsible for year-to-year variation in the influenza viruses; reason we must keep changing the makeup of the flu vaccine. (2: Antigenic Shift): Since RNA genomes of influenza are segmented they undergo reassortment (mixing up) if 2 different influenza viruses infect the same cell. Impt in understanding how influenza causes pandemics. When circulating human influenza virus infects an animal or bird host already infected w/ its own virus, segments of the 2 viruses can be mixed up & packaged together. When a foreign HA and/or NA ends up in a virus w/human segments encoding other proteins, we get a virus that can replicate in human cells but is not recognized at all by any human Abs. Pandemics occur when human populations are faced w/influenza viruses to which they have no immunity. Antigenic shift only occurs w/flu A, b/c these viruses infect both humans & animals.
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(MIDII #206)
INFLUENZA => Discuss the History of Influenza Pandemics and fears about future pandemics caused by Avian flu: A/H5N1. |
1918 Spanish flu killed 20-40 million ppl => result of antigenic shift. Most recent shift occurred in 1968 (Hong Kong flu), and drifted variants of this flu (A/H3N2) are predominant strains circulating today. Flu shifts occur every 30 yrs. Avian flu A/H5N1 is the next big worry, killed 5 people and millions of birds in Hong Kong in the late 1990's. H5N1 has been circulating in birds for some time but this strain of H5N1 killed the birds. Humans could be infected; mortality rate in humans was over 50%. This flu strain has several virulence factors including a highly cleavable hemagglutinin that can be activated by multiple cellular proteases, a specific substitution in the polymerase basic protein 2 that enhances replication, and a substitution in nonstructural protein 1 that confers increased resistance to inhibition by IFNs and TNF-α in vitro and prolonged replication in swine, as well as greater elaboration of cytokines, particularly TNF-α, in human MФs exposed to the virus. Humans infected have exaggerated symptoms of the flu and die of primary influenza pneumonia. For the virus to make the jump to pandemic status it will need to be efficiently transmitted from person-to-person (not from bird-to-person) and it has not done this yet.
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(MIDII #207)
INFLUENZA => Clinical Manifestations |
Nasty, self-limited infection. Classic presentations require presence of fever above 101 along with at least one systemic symptom (myalgias, chills, malaise) and at least one respiratory symptom (cough, nasal discharge). The onset of symptoms is abrupt and occurs 1-2 days after acquisition of the virus. Systemic symptoms usually dissipate after 3-4 days but other symptoms can persist for up to 2 wks. GI symptoms other than anorexia are rare (no such thing as the stomach flu). Complications are quite common and can be deadly.
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(MIDII #208)
INFLUENZA => Pneumonia |
Most common complication of influenza infection. Can be primary viral pneumonia or secondary bacterial pneumonia. Primary influenza pneumonia virus directly infects the lower RT causing rapidly progressive bilateral pneumonia which is very often fatal. Influenza pneumonia is responsible for the overwhelming majority of deaths in pandemics, especially in otherwise healthy young adults. In older adults and those w/chronic medical conditions, secondary bacterial pneumonia is the major cause of mortality. Influenza infection allows pathogenic bacteria to secondarily infect the lung with a resulting bacterial pneumonia. Strep pneumo and Staph aureus are common post-influenza pulmonary pathogens.
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(MIDII #209)
INFLUENZA => Myositis, Neurologic Complications, Reye's Syndrome |
(1)MYOSITIS: Inflammation of the muscles is seen in children following some influenza B infections. Muscles of the legs are particularly involved. (2) Neurologic complications include a post-infectious encephalitis and Guillain-Barre syndrome. (3) Reye's syndrome involves changes in mental status and liver dysfunction. Seen in children with influenza and other viruses who are given aspirin. Mortality from increased intracranial pressure is high and aspirin is no longer recommended as an antipyretic in children.
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(MIDII #210)
INFLUENZA => Diagnosis |
Self-diagnosis on the basis of clinical symptoms is adequate for most people. Gold standard for lab diagnosis is virus culture, but this is time and labor consuming and is used primarily by state labs to monitor outbreaks. Rapid antigen tests are the current diagnostic tests of choice for influenza. These test are performed directly on pt samples and can be highly sensitive and specific. PCR is now available for influenza although it is not yet widespread.
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(MIDII #211)
INFLUENZA => Treatment |
Most ppl require only rest and fluids. Some will benefit from specific antiviral agents. (a) Amantidine and rimantadine are primary symmetric amines which interfere with viral uncoating by blocking the action if influenza A's M2 protein. If given within 48 hrs of onset of symptoms, these drugs can reduce duration of symptoms by 1-2 days. Very effective at preventing infection if given during an influenza outbreak. Unfortunately, many viruses are resistant to amantidine & rimantidine. Side effects (esp CNS effects) are a problem with these agents. Dose adjustments have to be made in elderly pts and in ppl w/renal insufficiency. (b) The neuraminidase inhibitors are preferable. Decrease duration of symptoms of influenza and prevent infections. Block neuraminidase activity. Effective against both flu A & B. Side effects are milder than amantidine & rimantidine and they work against viruses resistant to those drugs. However, NONE of these agents prevents the complications of influenza infection.
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(MIDII #212)
INFLUENZA => Prevention |
Trivalent inactivated influenza vaccine is the mainstay of prevention. Vaccine is made up of inactivated viruses thought to circulate in the coming flu season. Since the virus is inactivated it is IMPOSSIBLE to get the flu from the flu vaccine. Efficacy of the vaccine is 50-80% and is lower in elderly & immunosuppressed populations. Vaccine reduces hospitalizations by 70% and death by 80% in these groups so it's definitely worth giving. Recommended that all individuals >50 receive the vaccine along w/anyone w/cardiac, pulmonary (asthma included), or renal disease, & ppl w/diabetes, hemoglobinopathies, immunosuppressive illnesses. Residents of nursing homes should be vaccinated as should caregivers of any of the above groups. Takes 2 wks for protective Ab to develop and Ab titers decline over several months. Optimal time to get the flu vaccine is from October to mid-November in the US. Yearly vaccination is req'd for cont'd protection. 5% of vaccinees will experience low grade fever and mild systemic symptoms. 30% will notice some tenderness at the vaccination site.
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(MIDII #213)
INFLUENZA => Discuss the Live Attenuated Nasally Administered Vaccine |
A live attenuated nasally administered vaccine was approved 2 yrs ago for prevention of influenza in healthy individuals aged 5-49. Will soon be approved for infants as young as 6 months and for older adults. It is highly efficacious. Shedding and some limited transmission of the vaccine virus has been seen; however, it remained attenuated and no-one got sick.
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(MIDII #214)
RESPIRATORY SYNCYTIAL VIRUS => General Description |
RSV is a member of paramyxoviridae family (which includes the parainfluenza viruses, mumps, and measles viruses). Most common cause of bronchiolitis in infants. Major contributor to morbidity & mortality especially in premature infants and the elderly. RSV is an enveloped, single-stranded, negative sense RNA virus. Genome encodes 10 viral proteins: (a) the glycosylated surface proteins F, G, and SH which mediate attachment of the virus to its host cell and fusion of viral w/host membranes. (b) proteins N, L, and P are associated w/the nucleocapsid. (c) M and M2 are non-glycosylated matrix proteins. (d) NS 1 and NS 2 are highly conserved non-structural proteins that may play a role in RNA replications.
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(MIDII #216)
RSV => Epidemiology |
Ubiquitous virus. Outbreaks occur every year: seasonality in winter and early spring. Begin in Nov, peak in Jan, continue 'til Apr. Virtually all kids are infected by age 2. Serious illness is more common in young infants. Boys & kids from lower socioeconomic backgrounds are more at risk for serious disease. Particularly at risk: preemies, esp w/bronchopulmonary dysplasia, kids w/congenital heart disease, kids w/pulmonary disease. RSV is impt pathogen in the elderly w/hospitalizations for complications of RSV disease being as common in this group as hospitalizations for influenza.
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(MIDII #217)
RSV => Clinical Manifestations |
Primary infection w/RSV is usually symptomatic. Lower RT involvement is most often seen in primary RSV infections. Pneumonia & bronchiolitis are seen most commonly in infants w/primary infection. Symptoms start w/nasal congestion, sore throat & fever. Cough develops in 1st few days, becomes deeper & more prominent as infection proceeds. Increased resp rate; retraction of lower intercostal muscles. Duration of symptoms: 7-21 days. Hospitalization rates due to lower RT involvement ~ 40% in infants <6 mo. Infection in adults & older kids is rarely asymptomatic despite previous immunity. Nasal congestion & cough mimicking common cold are the most common manifestations. Older adults at greater risk for serious infection than younger adults. Mortality from RSV pneumonia almost 20% in older adults. Immunocompromised individs at particular risk. Kids w/SCID & adults w/transplants & hematologic malignancies are at particular risk of fatal lower RT infections. Many infections are acquired nosocomially as RSV spreads very efficiently in hospitals.
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(MIDII #218)
RSV => Treatment |
Supportive care is mainstay of therapy in management of seriously ill infants. Supplemental oxygen should be given to hypoxic infants. Efficacy of bronchodilators is questionable although they are routinely used. Ribavirin: broad spectrum antiviral, works by interfering with viral RNA polymerase activity & inhibiting inosine 5'-monophosphate dehydrogenase which depletes intracellular nucleotide pools). Currently approved for Rx of lower tract RSV disease. Usually administered by aerosol and is generally reserved for high-risk pts.
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(MIDII #219)
RSV => Prevention |
Prevention reqs strict hand-washing and avoidance of secretions. Difficult to accomplish at home but in hospitals use of gown and glove isolation, strict hand washing and cohorting of infected pts is warranted. To prevent RSV infection in high risk infants, RSV Ig or a monoclonal Ab against RSV (PALIVIUMAB) may be used. Palivizumab is currently the preferred agent. Either is given 1x/month to high risk infants, significantly reduces severity & # of RSV infections. Use should be considered in any pre-term infant < 32 wks gestation who will be < 6 mo at onset of RSV season (Nov). Also used in RSV outbreaks in neonatal ICUs and in young kids w/bronchopulmonary dysplasia who require O2 or who have been off O2 for < 6 mo @ start of RSV season. RSV Ig doesn't benefit kids w/congenital heart disease. There is NO vaccine against RSV.
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(MIDII #220)
Rhinoviruses => Molecular Biology/General Description |
Rhinoviruses are most frequently associated w/common cold symptoms: 30% of upper RT infections. Small, non-enveloped single-stranded RNA viruses. They are members of picornaviridae family which include the enteroviruses (polioviruses, coxsackieviruses, echoviruses, & other enteroviruses) and hep A virus. 110 rhinovirus serotypes, enormous diversity makes vaccine development impossible. Optimal growth at 33 deg. C, corresponds to temp of the nose and large airways. Majority of rhinovirus serotypes uses a single cellular receptor-intercellular adhesion molecule (ICAM-1), which is found on many cell type surfaces. Cell surface ligand for LFA-1, impt role in immunologic and inflammatory rxns. Smaller group utilizes members of the low-density lipoprotein receptor family.
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(MIDII #221)
RHINOVIRUSES => Pathogenesis |
Enter nasopharynx thru nasal or ophthalmic mucosal (by touching nose or eyes). Viral replication occurs in nonciliated lymphoepithelial cells of the nasopharynx. Primary infection involves adenoidal tissues. Small number of epithelial cells are infected. Viremia does not occur. Rhinoviruses enter thru ICAM-1. Found on luminal surface of nonciliated lymphoepithelial cells in the nasopharynx, in the endothelial cells of the microvasculature, & in the germinal centers of the pharyngeal lymph nodes. Virus is deposited in nares & conjunctiva of the host, transported to the nasopharynx via mucociliary action, encounters ICAM-1 rich adenoidal crypts. Infection spread anteriorly along the nasal passages. Infection of the lower airways by rhinovirus may be more common in children. Fatal rhinovirus pneumonia and histologic evidence of rhinovirus in alveolar cells have been described in infants.
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(MIDII #222)
It used to be assumed that, like influenza and adenovirus, the symptoms associated with rhinovirus resulted from direct cytopathic effects on infected epithelial cells. Is this the case? |
In situ hybridization of the nasal mucosa biopsy specimens suggest that only a few cells are infected and cytopathology is conspicuously absent. Host inflamm rxn, NOT direct viral damage, is responsible for symptoms of the common cold. Elevated levels of pro-inflamm cytokines (IL-6, IL-8), TNF-alpha and GM-CSF have been documented during rhinovirus infection. IL-8 induces proinflamm changes associated w/infection. IL-8 Cx increases proportionally w/severity of rhinorrhea & nasal obstruction. Rhinovirus interacts w/its receptor, resulting in release of IL-8.
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(MIDII #223)
Rhinovirus => Epidemiology |
Most adults experience between 1-3 acute respiratory illnesses per yr. Infants <1 yr have highest rates of illness, w/avg of 6.1 infections per yr. Rates decline steadily w/increased age except for a slight increase in the 20-29 yr old age group. Due to presence of children in the home, supported by higher rates of illness in women in this age group who are primary caregivers for their kids. Multiple serotypes simultaneously present in the community, antigenic drift, and reinfection possibility permit multiple infections within a single individual; contribute to frequency of rhinovirus infections. 80% of infections are associated w/clinical illness. Illness is mild. Infected ppl don't seek medical attn.
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(MIDII #224)
Rhinoviruses => Seasonal Pattern Do rhinoviruses display a seasonal pattern of infection? |
Well-established seasonal pattern in temperate climates. Peaks are seen in early fall & spring. Rhinovirus activity is low in the winter w/coronaviruses & other agents are responsible for more debilitating winter colds. In tropical climates rhinovirus activity is greatest during the rainy season. Not known why. Seasonal changes in living conditions account for outbreaks. Environmental temperatures do not affect infection rates or severity of illness, despite popular belief exposure to cold or rainy weather does not affect host resistance to rhinovirus infection.
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(MIDII #225)
Rhinoviruses => Transmission |
Spread from person-to-person throughout communities via virally contaminated respiratory secretions. In homes or schools (relatively closed communities) spread is very efficient; secondary attack rates of 25-70%. Spread of rhinovirus colds among ppl at work is less common. Direct contact w/infected secretions & aerosols are efficient means of rhinovirus spread. Rhinoviruses can survive on environmental surfaces for several hrs. Porous materials such as tissues and cotton handkerchiefs do NOT allow virus survival and are NOT efficient modes of virus transmission. Decontamination of environmental surfaces w/virucidal disinfectants like Lysol decreases rate of transmission.
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(MIDII #215)
RSV => Pathogenesis Is Cell-Mediated Immunity or Humoral Immunity involved in viral pathogenesis? Which combination of these immunities contributes to infection? Which type of immunity is important for protection from severe disease with respiratory syncytial virus? |
Presence of RSV is detected by characteristic formation of syncytia (cells which have fused to form multinucleated giant cells). RSV is inoculated thru eyes or nose. Infection is confined to the RT. May involve upper RT or may spread to involve entire lower RT. In lower RT involvement, pathology shows a lymphocytic peribronchiolar infiltrate w/edema of the bronchial walls. Later, proliferation & necrosis of the bronchioles develops. Collections of sloughed epithelium lead to obstruction of small bronchioles and subsequent air trapping. Reabsorption of trapped air leads to atelectasis (collapse of parts of the lung) esp in young children. Viral infection in alveolar spaces can lead to frank viral pneumonia w/syncytia formation.
Infections occur when Abs are high and cellular immunity is low (during infancy or late adulthood). Infants given an RSV vaccine had MORE serious illness than UNvaccinated infants so immunologic mechanisms probably play a role in RSV pathogenesis (non-protective Abs are not helpful). Immunity to RSV is incomplete so reinfections are common. Cell-mediated immunity is impt & necessary to protect against severe disease. |
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(MIDII #216)
RSV => Epidemiology |
Ubiquitous virus. Outbreaks occur every year: seasonality in winter and early spring. Begin in Nov, peak in Jan, continue 'til Apr. Virtually all kids are infected by age 2. Serious illness is more common in young infants. Boys & kids from lower socioeconomic backgrounds are more at risk for serious disease. Particularly at risk: preemies, esp w/bronchopulmonary dysplasia, kids w/congenital heart disease, kids w/pulmonary disease. RSV is impt pathogen in the elderly w/hospitalizations for complications of RSV disease being as common in this group as hospitalizations for influenza.
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(MIDII #217)
RSV => Clinical Manifestations |
Primary infection w/RSV is usually symptomatic. Lower RT involvement is most often seen in primary RSV infections. Pneumonia & bronchiolitis are seen most commonly in infants w/primary infection. Symptoms start w/nasal congestion, sore throat & fever. Cough develops in 1st few days, becomes deeper & more prominent as infection proceeds. Increased resp rate; retraction of lower intercostal muscles. Duration of symptoms: 7-21 days. Hospitalization rates due to lower RT involvement ~ 40% in infants <6 mo. Infection in adults & older kids is rarely asymptomatic despite previous immunity. Nasal congestion & cough mimicking common cold are the most common manifestations. Older adults at greater risk for serious infection than younger adults. Mortality from RSV pneumonia almost 20% in older adults. Immunocompromised individs at particular risk. Kids w/SCID & adults w/transplants & hematologic malignancies are at particular risk of fatal lower RT infections. Many infections are acquired nosocomially as RSV spreads very efficiently in hospitals.
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(MIDII #218)
RSV => Treatment |
Supportive care is mainstay of therapy in management of seriously ill infants. Supplemental oxygen should be given to hypoxic infants. Efficacy of bronchodilators is questionable although they are routinely used. Ribavirin: broad spectrum antiviral, works by interfering with viral RNA polymerase activity & inhibiting inosine 5'-monophosphate dehydrogenase which depletes intracellular nucleotide pools). Currently approved for Rx of lower tract RSV disease. Usually administered by aerosol and is generally reserved for high-risk pts.
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(MIDII #219)
RSV => Prevention |
Prevention reqs strict hand-washing and avoidance of secretions. Difficult to accomplish at home but in hospitals use of gown and glove isolation, strict hand washing and cohorting of infected pts is warranted. To prevent RSV infection in high risk infants, RSV Ig or a monoclonal Ab against RSV (PALIVIUMAB) may be used. Palivizumab is currently the preferred agent. Either is given 1x/month to high risk infants, significantly reduces severity & # of RSV infections. Use should be considered in any pre-term infant < 32 wks gestation who will be < 6 mo at onset of RSV season (Nov). Also used in RSV outbreaks in neonatal ICUs and in young kids w/bronchopulmonary dysplasia who require O2 or who have been off O2 for < 6 mo @ start of RSV season. RSV Ig doesn't benefit kids w/congenital heart disease. There is NO vaccine against RSV.
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(MIDII #220)
Rhinoviruses => Molecular Biology/General Description |
Rhinoviruses are most frequently associated w/common cold symptoms: 30% of upper RT infections. Small, non-enveloped single-stranded RNA viruses. They are members of picornaviridae family which include the enteroviruses (polioviruses, coxsackieviruses, echoviruses, & other enteroviruses) and hep A virus. 110 rhinovirus serotypes, enormous diversity makes vaccine development impossible. Optimal growth at 33 deg. C, corresponds to temp of the nose and large airways. Majority of rhinovirus serotypes uses a single cellular receptor-intercellular adhesion molecule (ICAM-1), which is found on many cell type surfaces. Cell surface ligand for LFA-1, impt role in immunologic and inflammatory rxns. Smaller group utilizes members of the low-density lipoprotein receptor family.
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(MIDII #221)
RHINOVIRUSES => Pathogenesis |
Enter nasopharynx thru nasal or ophthalmic mucosal (by touching nose or eyes). Viral replication occurs in nonciliated lymphoepithelial cells of the nasopharynx. Primary infection involves adenoidal tissues. Small number of epithelial cells are infected. Viremia does not occur. Rhinoviruses enter thru ICAM-1. Found on luminal surface of nonciliated lymphoepithelial cells in the nasopharynx, in the endothelial cells of the microvasculature, & in the germinal centers of the pharyngeal lymph nodes. Virus is deposited in nares & conjunctiva of the host, transported to the nasopharynx via mucociliary action, encounters ICAM-1 rich adenoidal crypts. Infection spread anteriorly along the nasal passages. Infection of the lower airways by rhinovirus may be more common in children. Fatal rhinovirus pneumonia and histologic evidence of rhinovirus in alveolar cells have been described in infants.
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(MIDII #222)
It used to be assumed that, like influenza and adenovirus, the symptoms associated with rhinovirus resulted from direct cytopathic effects on infected epithelial cells. Is this the case? |
In situ hybridization of the nasal mucosa biopsy specimens suggest that only a few cells are infected and cytopathology is conspicuously absent. Host inflamm rxn, NOT direct viral damage, is responsible for symptoms of the common cold. Elevated levels of pro-inflamm cytokines (IL-6, IL-8), TNF-alpha and GM-CSF have been documented during rhinovirus infection. IL-8 induces proinflamm changes associated w/infection. IL-8 Cx increases proportionally w/severity of rhinorrhea & nasal obstruction. Rhinovirus interacts w/its receptor, resulting in release of IL-8.
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(MIDII #223)
Rhinovirus => Epidemiology |
Most adults experience between 1-3 acute respiratory illnesses per yr. Infants <1 yr have highest rates of illness, w/avg of 6.1 infections per yr. Rates decline steadily w/increased age except for a slight increase in the 20-29 yr old age group. Due to presence of children in the home, supported by higher rates of illness in women in this age group who are primary caregivers for their kids. Multiple serotypes simultaneously present in the community, antigenic drift, and reinfection possibility permit multiple infections within a single individual; contribute to frequency of rhinovirus infections. 80% of infections are associated w/clinical illness. Illness is mild. Infected ppl don't seek medical attn.
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(MIDII #224)
Rhinoviruses => Seasonal Pattern Do rhinoviruses display a seasonal pattern of infection? |
Well-established seasonal pattern in temperate climates. Peaks are seen in early fall & spring. Rhinovirus activity is low in the winter w/coronaviruses & other agents are responsible for more debilitating winter colds. In tropical climates rhinovirus activity is greatest during the rainy season. Not known why. Seasonal changes in living conditions account for outbreaks. Environmental temperatures do not affect infection rates or severity of illness, despite popular belief exposure to cold or rainy weather does not affect host resistance to rhinovirus infection.
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(MIDII #225)
Rhinoviruses => Transmission |
Spread from person-to-person throughout communities via virally contaminated respiratory secretions. In homes or schools (relatively closed communities) spread is very efficient; secondary attack rates of 25-70%. Spread of rhinovirus colds among ppl at work is less common. Direct contact w/infected secretions & aerosols are efficient means of rhinovirus spread. Rhinoviruses can survive on environmental surfaces for several hrs. Porous materials such as tissues and cotton handkerchiefs do NOT allow virus survival and are NOT efficient modes of virus transmission. Decontamination of environmental surfaces w/virucidal disinfectants like Lysol decreases rate of transmission.
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(MIDII #236)
HIV and AIDS => Natural Hx of HIV Infection (1)Does HIV have a period of clinical latency? Microbial latency? (2)When HIV is difficult to culture, is the HIV virus still replicating? (3)When are levels of viremia highest? (4)At what point is a viral set point established and what does this set point predict? |
(1) HIV is a chronic, progressive process w/a variable period of clinical latency but NO microbial latency. (2) Virtually all pts have evidence of active viral replication at all times. (3) Levels of viremia are highest right after infection and then actively suppressed by a host cellular immune response after a few months. (4) A set point is established for concentration of HIV RNA in plasma by 6 months which is predictive for the subsequent course of HIV disease.
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(MIDII #237)
HIV and AIDS => Natural Hx of HIV Infection (1)What is the hallmark of the progressive immunodeficiency of HIV disease? (2)What is the outcome of untreated HIV disease? How do treatments ameliorate disease course? |
(1)CD4+ T cell depletion is the hallmark of HIV. There is a series of CD4 levels below which risk of specific opportunistic infections rise greatly; valuable in targeting diagnostic evaluations and using specific prophylactic mechanisms. (2) Ultimate outcome of untreated disease is progression to AIDS and death in nearly all pts. Better clinical care w/prophylaxis of opportunistic infections extends survival. Combination anti-retroviral therapy can reverse even severe immunodeficiency, reducing risk of opportunistic infections or death dramatically.
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(MIDII #238)
HIV and AIDS => Natural Hx of HIV Infection (1) What accounts for variability in speed of HIV progression? (2) What distinguishes long-term progressors from other patients? |
There is substantial variability in HIV's course. (1) Viral load setpoint accounts for most variability seen in the speed of HIV progression. (2) Long-term non-progressors are a small subgroup (5-10%) who have relatively normal CD4 counts (>500) and no HIV-related disease for 10 yrs or more without anti-retroviral therapy. Maintain much lower HIV viral loads than pts starting at same time after infection w/same CD4 count who have more rapidly progressing disease.
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(MIDII #239)
HIV and AIDS => Acute Retroviral Syndrome (1) Do all HIV infected pts display an “acute retroviral syndrome”? (2) What impact does the severity of clinical symptoms associated with this syndrome have on disease progression, if any? (3) What clinical beneift, if any, is associated with identifying pts at the onset of infection? |
(1) Only 20% of HIV pts seek care for a clinical illness coinciding w/appearance of HIV Abs several wks to a few months after HIV infection. Usually mild, self-limited, and non-specific. Clinical features include fever, fatigue, sore throat, lymphadenopathy, and a macular erythematous rash. (2) Severity of these initial symptoms predicts more rapid progression of HIV infection than in pts with few or no symptoms. (3) Identifying pts at onset of infection may have a significant therapeutic benefit => antiretroviral therapy at this early stage can extend the time to disease progression. Under investigation whether viral load set point may reset to a lower level when pts are treated for approximately 1 yr after acute infection and then stop HIV therapy.
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(MIDII #240)
HIV and AIDS => Asymptomatic Phase of HIV Infection (1)Are CD4 cells depleted during the variable asymptomatic period (during which there is ongoing viral replication but no symptoms of infection or its complications)? (2) What are 3 compelling reasons for early identification of HIV positive, asymptomatic pts? |
(1)Progressive CD4 cell depletion characterizes the variable asymptomatic period. Average pt has a viral load setpoint of 30,000 copies of HIV-1 RNA per ml of plasma and loses 50 CD4+ T cells per year. There are NO symptoms in most pts during this time. (2) There are compelling reasons to ID HIV positive asymptomatic patients: (a) Behavior changes can be made to lower or eliminate risk of further transmission of HIV; (b) Prophylactic regimens to prevent life-threatening opportunistic infections can be utilized based on CD4 cell risk staging; (c) If antiretroviral treatment is initiated before the late stages of HIV disease immune deterioration can be halted or reversed before complications develop.
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(MIDII #241)
HIV and AIDS => Early Manifestions of HIV Disease Discuss some of the clinical manifestations which occur more often in HIV patients as prodromal events (although they are not HIV-specific). |
These illnesses include bacterial pneumonia esp due to S. pneumoniae, herpes zoster, new onset or major flares of psoriasis and sebhorreic dermatitis, salmonella septicemia; and increasingly frequent or severe recurrences of ano-genital Herpes simplex. Most of these events are associated with moderately advanced immunodeficiency and are quickly followed by an AIDS-defining event if HIV infection is not recognized and prophylaxis initiated. There are 2 exceptions: Herpes zoster may precede AIDS by years, as well as tuberculosis. Any of these manifestations in an individual with hx of HIV risk behavior or otherwise healthy young adults should raise possibility of HIV infection.
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(MIDII #242)
HIV and AIDS => Prognostic Markers for the Course of HIV Disease |
Absolute value of the CD4 count is the best surrogate marker to predict time to AIDS, risk of specific opportunistic infections, or death, especially once counts have fallen from the normal range of 800-1200 to 300 or less. The CD4% by itself is less accurate prognostically. Immune activation markers (neopterin, beta-2 microglobulin) may add to precision of CD4. Combining HIV-1 viral load measurement w/CD4 count provides an accurate prediction of risk of developing AIDS 5 yrs in the future, even w/pts with nearly normal CD4 counts at baseline.
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(MIDII #243)
HIV and AIDS => Clinical Features: Spotlight on PNEUMOCYSTIS PNEUMONIA (PCP) (1)Pathogen (2)Risk factors (3)Pathogenesis |
(1: Pathogen) Pneumocystis is a fungus. Most ppl become exposed during childhood; fungus is widely distributed. Caused by pneumocystis jirovecii. (2: Risk Factors) Prototypic opportunistic pathogen, initially implicated in nursery outbreaks among malnourished infants. Prior to AIDS, encountered in US in congenitally immunodeficient or iatrogenically immunosuppressed transplant & cancer pts. Most AIDS pts w/PCP have CD4 counts <200. Pts w/higher counts (>350) and symptoms like oral thrush, fever, & wt loss are at high risk as well. Reinfection rather than reactivation accounts for some cases but secondary cases/outbreaks have not been well-documented. (3: Pathogenesis) Proliferation in alveoli leading to exudative response produces typical disease. Hematogenous dissemination occurs in some cases. Extrapulmonary involvement at numerous sites has been encountered.
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(MIDII #244)
HIV and AIDS => Clinical Features: Spotlight on Pneumocystis Pneumonia (1)Clinical Features (2)Diagnosis (3)Treatment (4)Prevention |
(1: Clinical Features) Fever & dry cough w/slowly progressive dyspnea (over 4 wks) are common. Chest X-ray may show diffuse interstial infiltrate or various localized abnormalities. Severe disease is defined by an A-a gradient >35 or pO2 <70. (2: Dx) No culture, antigen detection, or serologic diagnostic procedure is available. Dx rests on histological ID of cysts or trophozoites. Lung biopsy is definitive. Alveolar contents obtained by bronchoscopic lavage has excellent yield. (3: Rx) Trimethoprim-sufamethoxazole or pentamidine isethionate have comparable efficacy. High rate of drug intolerance so they've looked for other agents. Atovaquone is approved only for mild-moderate disease w/limited bioavailability & efficacy. Dapsone w/trimethoprim, or clindamycin w/primaquine are other alternatives. Pts progressing to respiratory failure have a high mortality rate. No salvage regimen has been found. Early use of systemic corticosteroids in pts w/severe disease can lower mortality by 50%. (4: Prevention) TMP-SMZ orally is the most effective agent (failure rate <5%). Dapsone or aerosolized pentamidine (given by inhalation monthly) are good but far less effective alternatives.
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(MIDII #245)
HIV and AIDS => Clinical Features: Spotlight on TOXOPLASMOSIS (1)Microbiology (2)Risk Factors (3)Pathogenesis (4)Clinical Manifestations |
(1)Toxoplasma gondii is a protooon parasite of members of the cat family. Affects other animals (incl humans) who ingest fecally excreted oocysts which survive in the environment or who ingest organisms encysted in skeletal muscle of domestic animals (undercooked meat). (2: Risk Factors) Prior infection as indicated by serum Abs is a reliable way to establish risk. Some cases have been reported in sero-negatives. CD4 counts <100 when toxoplasmosis develops. IgG Abs are reliable indicator of prior infection and population studies show dramatically different rates between populations. (3: Pathogenesis) Reactivation of a dormant cyst. Most disease is recognized in the brain, although cysts are widely distributed throughout skeletal and smooth muscle. (4: Clinical) Cases present as focal CNS events consistent with an expanding mass lesion. Seizures, motor defects or a “stroke” are most common.
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(MIDII #246)
HIV and AIDS => Clinical Features: Spotlight on TOXOPLASMOSIS (1)Diagnosis (2)Treatment (3)Prevention |
(1: Diagnosis) => Typical clinical presentation plus focal lesions on head CT or MRI in an HIV positive pt w/T gondii Abs is sufficient to begin therapy. Characteristically, symptomatic & radiologic improvement is evident after 1-2 wks treatment. Diagnostic brain biopsy needed if no response. (2: Treatment) => A combo of pyrimethamine and sulfadiazine is standard and reliably effective but not tolerated for long-term use. Clindamycin can substitute for sulfa drugs. Long-term suppression with one of these combos is needed. (3: Prevention) => Trimethoprim-sulfamethoxazole lowers risk of toxoplasmosis compared to dapsone or aerosolized pentamidine. Individuals w/ T gondii Abs and CD4 counts less than 100 should have pyrimethamine added to dapsone or pentamidine PCP prophylaxis if they are unable to tolerate TMP-SMZ.
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(MIDII #247)
HIV and AIDS => Clinical Features: Spotlight on TB (1)Risk Factors (2)Pathogenesis (3)Clinical Manifestations |
(1: Risk Factors) Globally, TB is greatest cause of HIV-associated mortality. Past infection or recent infection are impt contributors to high rate of TB in HIV pts. (2: Pathogenesis) HIV is most powerful accelerant to promote activation of latent TB infection. Reinfection w/new strains occurs in AIDS pts; also increased susceptibility to primary infection. Lack effective cell-mediated immunity so pts w/advanced HIV disease experience reactivation of dormant TB infection at a high rate, but don't develop immune responses producing characteristic lung cavities & productive sputum (that you'd see in non-HIV pts). PPD rxn may be absent making Dx difficult. (3: Clinical) TB can occur in HIV pts at any CD4 count but frequency/severity rise & manifestations change as CD4 count drops. Pulmonary disease most common. Typical pattern of apical cavity on x-ray, productive cough, AFB (+) sputum smear is less common at low CD4 counts. Hilar adenopathy & lower lobe infiltrates in these pts may reflect atypical reactivation, primary infection, or reinfection. Proportion of TB cases w/disseminated or extrapulmonary disease is ↑ in advanced HIV infection.
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(MIDII #248)
HIV and AIDS => Clinical Features: Spotlight on TB (1)Diagnosis (2)Treatment (3)Prevention |
(1: Dx) TB is defined by reactive PPD (>/= 5 mm) in an HIV infected pt. Many pts w/advanced HIV are anergic. Typical cases of active pulmonary disease are easy to detect, but many outbreaks start when atypical presentations are missed. Sputum AFB smears are only (+) in 50% of cases. An aggressive, invasive approach may be needed to detect extrapulmonary sites. Culture takes several wks. Rapid tests (PCR) are helpful if (+) but false (-) results may occur. (2: Rx) Standard therapy works well for sensitive isolates. 6-9 months of Rx is recommended. Drug resistant TB epidemics have been centered in AIDS treatment facilities; characterized by very high early mortality rates. Therapy for resistant TB is best guided by sensitivity test results. (3: Prevention) Strict adherence to isolation protocols is vital to avoid nosocomial infection. INH prophylaxis (for 9 rather than 6 months) is effective in PPD+/HIV+ pts.
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(MIDII #249)
HIV and AIDS => Clinical Features: Spotlight on Cryptococcal Disease (1)Microbiology (2)Risk Factors (3)Pathogenesis (4)Clinical Manifestations |
(1: Microbio) Cryptococcus neoformans is a widely distributed soil fungus associated w/pigeon (bird) droppings. Polysaccharide capsule is antiphagocytic and a major virulence factor. (2: Risk Factors) Cryptococcal infection usually begins as subclinical pulmonary infection leading to silent hematogenous dissemination. Most AIDS pts w/cryptococcosis have severe immunodeficiency (CD4 </= 100). (3: Pathogenesis) Reactivation of foci seeded during primary infection occurs when immunity is compromised. Reactivation cryptococcal disease can occur in apparently normal, HIV negative ppl as well. (4: Clinical) Meningitis is the most common cryptococcal syndrome in AIDS pts. Mild headache, low grade fever. Stiff neck & major mental status compromise are uncommon. Widespread dissemination throughout body is frequent, involving lungs, pleura, mediastinal nodes, skin. Blood cultures are often (+).
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HIV and AIDS => Clinical Features: Spotlight on Cryptococcal Disease
(1)Diagnosis (2)Treatment (3)Prevention |
(1: Dx) CSF is usually only mildly abnormal, with lymphocyte pleocytosis and elevated protein. But the test for cryptococcal antigen is almost always (+) in CSF culture. (2: Rx) IV Amphotericin B is the mainstay of acute therapy. Addition of 5-fluorocytosine may be helpful. Long-term suppression w/oral fluconazole is highly effective. (3: Prevention) Use of fluconazole to prevent fungal disease in HIV+ pts w/low CD4 counts is effective in lowering incidence of cryptococcal & candida disease but NOT mortality. Due to lack of mortality effect and concern about fluconazole-resistant candida, routine use of this prophylactic regimen is NOT recommended.
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(MIDII #250)
HIV and AIDS => Clinical Features: Spotlight on MYCOBACTERIUM AVIUM COMPLEX DISASE (1)Microbiology (2)Risk Factors (3)Pathogenesis (4)Clinical Manifestations |
(1: Micro) M.avium and M.intracellulare are soil & water organisms widely distributed throughout the world. Referred to as MAC b/c difficult to distinguish. Isolated as saphrophytes from sputum in immunologically intact hosts. (2: Risks) Exposure is more intense in certain regions (Southeastern US). HIV infected pts w/very advanced disease (CD4 < 50) at risk for disseminated MAC infection. (3: Path) Reactivation of dormant MAC focus is usual pattern of disease. Re-infection via GI route may be common. Loss of immune control (deficient IFN-γ production) may account for disseminated MAC in AIDS pts. Never seen in other comparably immune deficient HIV-neg pts. (4: Clinical) Disseminated MAC presents in indolent, non-specific fashion in pts who are already chronically ill w/advanced HIV disease. Fever, weight loss, anemia, diarrhea. Hepatosplenomegaly reflects massive infiltration of reticuloendothelial viscera by MAC. Skin, lungs, & brain are RARELY sites of involvement.
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(MIDII #251)
HIV and AIDS => Clinical Features: Spotlight on MAC Disease (1)Diagnosis (2)Treatment (3)Prevention |
(1: Dx) Biopsy with acid fast staining of affected organs is a reliable means of diagnosis. Blood culture on appropriate media is usually sufficient since there is a high level of mycobacteremia in most pts. (2: Rx) MAC organisms are resistant to standard anti-mycobacterial drugs. Macrolides clarithromycin & azithromycin are main therapeutic agents. Treatment calls for one of these drugs in combo w/one additional agent (Ethambutol or Rifabutin) to prevent resistance. Treatment is lifelong – this regimen is only suppressive and relapses are common. (3: Prevention) Rifabutin, Clarithromycin, and Azithromycin have been approved for preventing MAC. Major concern is development of resistance (50% of pts w/breakthrough mycobacteremia while on clarithromycin will have resistant organisms) which then removes the best agent for treating MAC disease.
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(MIDII #252)
HIV and AIDS => Clinical Features: Spotlight on CYTOMEGALOVIRUS (CMV) DISEASE (1)Microbiology (2)Risk Factors (3)Pathogenesis (4)Clinical Manifestations |
(1: Micro) CMV is a herpes group DNA virus. Establishes latent infection w/intermittent asymptomatic shedding. Commonly acquired thru sexual or other exposure to infectious oral or urogenital secretions. ½ of adults are seropositive. (2: Risks) CMV infections occur in most advanced stages of HIV diseases. Rarely the 1st HIV-related complications experienced by pt. Mean CD4 count: 29. Re-infection accounts for a portion of CMV episodes. (3: Pathogenesis) CMV disseminates throughout body. Persists in proviral state. Reactivation can occur anywhere. Loss of cellular immunity allows latent virus replication. CMV pneumonia is common in organ transplant pts but NOT in AIDS pts. Retinitis and GI tract involvement are most common in AIDS pts. CMV hepatitis is most common in liver transplant pts. (4: Clinical) Retinitis w/visual impairment & eventual blindness is major morbidity in AIDS pts. GI tract can be involved: oral & esophageal ulcers, gastritis, enteritis, colitis, intestinal perforation. CNS CMV disease is recognized as polyradiculopathy, encephalitis, ventriculitis.
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(MIDII #253)
HIV and AIDS => Clinical Features: Spotlight on CYTOMEGALOVIRUS (CMV) DISEASE (1)Diagnosis (2)Treatment (3)Prevention |
(1: Dx) Retinitis is diagnosed by pattern of hemorrage & exudate on ocular fundus exam. GI/other sites req biopsy confirmation since secretions are often (+) due to asymptomatic shedding of CMV in AIDS or immunocompromised pts, not specific for dx of active CMV disease. PCR of serum allows detection of CMV viremia. (2: Rx) Ganciclovir, Foscarnet, Cidofovir. Ganciclovir is now available in a well-absorbed valine ester form. The other 2 agents req IV administration for induction & long-term suppression. All 3 have substantial toxicity potential. Delay progression of CMV retinitis but do not stop it. Reinduction is often needed. Loss of vision may occur despite aggressive treatment. Another therapy is an intra-ocular implant which releases ganciclovir. Highly effective in the treated eye but no protection to other eye or systemically. (3: Prevention) Prophylaxis has not been routinely used b/c of toxicity & expense of agents.
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(MIDII #254)
HIV and AIDS => Clinical Features: Spotlight on Cryptosporidiosis and other infectious diarrheas. |
Diarrhea is a very common complain in HIV pts in late stages of disease. Cryptosporidium parvum causes self-limited if severe diarrhea in normal hosts. In AIDS pts it causes a chronic, watery diarrhea as severe as cholera and other secretory processes leading to hypovolemia, acidosis & death. Many other intestinal pathogens are associated w/increased frequency or severity of diarrhea in AIDS pts. 2 late stage opportunistic infections (MAC and CMV) may present w/diarrhea as dominant symptoms. No specific etiology is usually found for HIV diarrhea, treatment is usually symptomatic.
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(MIDII #255)
HIV and AIDS => Clinical Spotlight on Regional Mycoses |
Disseminated histoplasmosis and coccidiodomycosis are important AIDS opportunistic infections in endemic areas (the Midwest, Caribbean, and Central America for Histo and the Southwest and West for Cocci). Histoplasmosis can present in a variety of disseminated forms including a fulminant, septic syndrome.
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(MIDII #256)
HIV and AIDS => Clinical Spotlight on Neuropsychiatric Processes |
Nervous system is frequently involved in a variety of ways in AIDS pts. Painful peripheral neuropathy and subcortical dementia are prominent complications. Progressive multifocal leukoencephalopathy is an opportunistic, JC-virus induced white matter disease presenting as behavioral change or dementia in advanced AIDS pts. Depression, suicidality, pain control & substance abuse are other frequent issues in AIDS care.
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(MIDII #257)
HIV and AIDS => Clinical Spotlight on Malignancies |
Kaposi's Sarcoma (KS), Non-Hodkins lymphoma (NHL), and cervical cancer occur at increased frequency in AIDS. KS is strongly linked to male-to-male sex, and is caused by herpes virus 8 (HHV 8). Lymphoma is increased in advanced HIV disease esp primary CNS lymphoma. Early detection of cervical dysplasia through frequent pap smears is an effective control strategy. Current therapy for KS or NHL is palliative w/chemo or radiotherapy. The best therapy: restoration of immune control by effective anti-retroviral therapy.
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(MIDII #258)
HIV and AIDS => Clinical Spotlight on Wasting Syndrome and Nutrition Issues |
Weight loss is a common feature of AIDS. Often attributable to chronic systemic infections and/or a GI infiltrative, ulcerative, or diarrheal disease. Weight restoration occurs with successful treatment of OI, or w/initiation of anti-retroviral therapy. Nutritional supplements and dietary counseling might be helpful for some pts. Severe unexplained weight loss in an HIV infected pt is an AIDS defining event. Neither pathogenesis nor treatment are clear, but there is interest in therapy w/growth hormone, testosterone, anabolic steroids, and anti-tumor necrosis factor agents.
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(MIDII #259)
(1)What parts of the viral life cycle are potential antiviral targets for HIV? (2) What are the 5 classes of FDA approved anti-retroviral agents? (3) Are drugs used independently or in combination? (4) Why are current therapies imperfect? |
(1)Every step in the viral life cycle is a potential antiviral target. (2) 5 classes of anti-retroviral agents approved by the FDA: (a) Nucleoside analog reverse transcriptase (RT) inhibitors [NsRTI's]; (b) Nucleotide analog RT inhibitors [NtRTI's]; (c) Non-nucleoside RT inhibitors (NNRTI's); (d) Protease Inhibitors (PI's); (e) Entry (fusion) inhibitors. (3) Drugs must be used in combination to be effective. (4) Current therapies are imperfect due to the complexities of some regiments; toxicities; and drug resistance.
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(MIDII #260)
NUCLEOSIDE ANALOG REVERSE TRANSCRIPTASE INHIBITORS (NsRTIs) to treat HIV |
(1) Approved nucleoside analog reverse transcriptase inhibitors (NsRTI's) include: Zidovudine (ZDV, AZT), Didanosine (ddI), Zalcitabine (ddC), Stavudine (d4T), Lamivudine (3TC), Abacavir (ABC), Emtricitabine (FTC). (2) NsRTIs were the 1st class of anti-HIV agents developed, work against HIV-1 and HIV-2. (3) Parent cmpds are NOT active. Need to undergo intracellular anabolic phosphorylation to the triphosphate (TP) form of the drug to be active vs HIV. (3) MOA: NsRTIs inhibit the HIV RT by competing with normal nucleoside triphosphates for incorporation into the growing proviral DNA chain. Viral DNA chain elongation is terminated prematurely b/c the absence of the 3'-OH sugar moiety prevents addition of another nucleotide. Viral replication ceases.
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(MIDII #261)
NUCLEOTIDE ANALOG REVERSE TRANSCRIPTASE INHIBITOR (NtRTIs) to treat HIV |
(1)Tenofovir disoproxil fumarate (TDF) is FDA approved prodrug of tenofovir. Lead cmpd in the 4th class of antiretroviral agents approved for clinical use. (2) Nucleotides contain a phosphate group, so only need to be diphosphorylated intracellularly to be metabolized to their active forms. (3) MOA => Tenofovir-diphosphate is the active moiety and acts as a competitive inhibitor of the HIV RT in the same fashion as nucleoside analog triphosphates.
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(MIDII #262)
NON-NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS (nnRTIs) to treat HIV |
(1)FDA approved nnRTIs are Nevirapine (NVP), Delavirdine (DLV), and Efavirenz (EFZ). (2) NNRTIs were the 2nd class of anti-HIV drugs developed. Potent but subject to rapid emergence of resistance. Active vs. HIV-1 only (except Group O). Inactive vs. HIV-2 (impt in areas of the world where HIV-2 is seen => West Africa, immigrants to Europe). (3) In contrast to NRTIs, the parent molecules are the active moieties so they are immediately active once they enter the cell. (4) MOA => NNRTI's inhibit the HIV-1 RT by binding to a hydrophobic pocket on the enzyme close to the active site, locking the enzyme in an inactive conformation. (5) Drug-drug interactions are a major problem w/NNRTIs. Metabolized by CYP3A4. Also, NVP & EFZ induce CYP3A4 while DLV inhibits CYP3A4. So potential for major DDIs w/numerous HIV (esp PI's) and non-HIV agents which are also metabolized by same hepatic pathway. So, DO NOT prescribe without first checking for potential DDIs. May be contraindications or need for dose adjustments.
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(MIDII #263)
PROTEASE INHIBITORS (PI's) to treat HIV |
(1)PI's were 3rd class of anti-HIV agents developed. Highly potent against HIV. Introduced in 1996. (2) Active against HIV-1 and -2. (3) MOA: Inhibit HIV protease by binding to the active site of the enzyme, preventing cleavage of gag and gag-pol precursor polyproteins at late stage of viral replication. Virions are produced by they are incomplete and non-infectious. (4) DDI's are major problem. Metabolized by CYP3A4. Inhibit CYP3A4 to varying degrees. Ritonavir is the most potent CYP3A4 inhibitor known. So low dose RTV has been used as a pharmacoenhancer of other PI's. Lopinavir is coformulated w/Ritonavir to enhance former's pharmacokinetic profile. Potential for major DDI's w/numerous HIV drugs (esp NNRTIs) and non-HIV agents. DO NOT prescribe w/o checking for DDI's. May be contraindicatons or need for dose adjustment(s).
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(MIDII #264)
FUSION INHIBITOR to treat HIV |
(1)Enfuvirtide, a fusion inhibitor, is a 5th class of antiretroviral agents approved by the FDA. (2) 36 aa peptide, binds to a region of the gp41 transmembrane glycoprotein of HIV and prevents virus-cell fusion. Must be given as a subcutaneous injection. Major toxicity is injection site rxns. Resistance can develop, characterized by development of aa substitutions in the gp41 protein that prevents proper binding of the inhibitor.
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(MIDII #265)
What factors should be taken into consideration when deciding when to initiate antiretroviral therapy in HIV patients? |
(1)Patient's disease stage as measured by (a) Symptomatic status. All symptomatic pts should be offered treatment irrespective of the CD4 count or plasma HIV-1 RNA level. (b) CD4 cell count: measure of immune status. (c) Plasma HIV-1 RNA level, reflective of the productively infected cell population in the body. (2) Pts commitment to therapy: drug adherence is critical to treatment success. (c) Philosophy of treatment: How aggressive the pt and physician wish to be w/treatment (starting earlier vs later) is an impt factor.
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(MIDII #266)
When should anti-retroviral therapy be started in an ASYMPTOMATIC person with HIV? |
Not clear. Delaying therapy until CD4 count falls below 200/mm^3 compromises ultimate outcome w/regard to developing an AIDS defining illness or death. Consensus: start therapy when CD4 count falls below 350/mm^3 to provide a safety margin for the pt. When CD4 count is above 350/mm^3, the level of plasma HIV-1 RNA is factored in. Predicts rate of CD4 cell count decline. Plasma HIV-1 RNA levels >100,000 copies/ml are independent predictors of disease progression in asymptomatic pts w/CD4 cell counts >350/mm^3.
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(MIDII #267)
Discuss Antiretroviral Regimens for HIV |
(A) NNRTI + 2 nucleoside RTI's are most widely prescribed at present. Newer option is NNRTI + 1 NsRTI + 1 NtRTI. This is PI sparing. (B) Protease Inhibitor (+/- low dose RTV) + 2 nucleoside RTI's. This is NNRTI sparing. (C) 3 nucleoside/nucleotide RTI's. PT and NNRTI sparing. No longer a first line option. Shouldn't be used, has a higher virologic failure rate. (D) 3 nucleoside RTI's + 1 NtRTI. PT and NNRTI sparing. Under investigation. (E) PI/low-dose RTV + 1 NNRTI + 1-2 NRTI's => consider only in special circumstances, acquisition of a drug-resistant virus. (F) PI/low-dose RTV + 1 NNRTI => NRTI sparing, currently in clinical trials.
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(MIDII #268)
What are the definitions for antiretroviral treatment failure for HIV? What are reasons for drug failure? |
(1)Definitions of treatment failure: (A) Clinical failure as measured by disease progression; (B) Immunologic failure as measured by CD4 cell count decline; (C) Virologic failure as measured by a rise in plasma HIV-1 RNA level above a certain threshold. (2) Reasons for Drug Failure => Development of drug resistance; Incomplete or poor drug adherence; Pharmacologic factors leading to diminished drug levels; Insufficiently potent regimens; Tissue or cell sanctuaries that allow virus to escape drug inhibitory effects; Cellular mechanisms of resistance which may lead to drug efflux from cells; Compromised host immune status which may facilitate higher degrees of viral replication.
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(MIDII #269)
Discuss HIV drug resistance. |
Genetic variants of HIV are continuously produced as a result of high viral turnover and inherent error rate of HIV's reverse transcriptase. Mutations at each base position occur daily. Survival of resulting viral mutants depends on the replication competence of the mutants and the presence of drug or immune selective pressure. Implications: resistant mutations exist before drug exposure and may emerge quickly after it is introduced. Drugs which develop high level resistance w/a single mutation are at greatest risk (3TC, FTC, NNRTI's) and resistance to agents which require multiple mutations will evolve more slowly (ZDV, PI's). So potent combo regimens need to be constructed that pose a high 'genetic barrier' for the virus to overcome.
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(MIDII #270)
What challenges remain in reducing HIV-related morbidity and mortality? Summarize! |
(A) Some regimens remain complex, particularly for treatment experienced pts. (B) Drugs have neg effects of quality of life even if no toxicities are apparent. (C) Toxicities: hyperlipidemia, fat redistribution, insulin resistance, decreased bone density, and mitochondrial dysfunction are a major focus of clinical concern and one reason why pts and clinicians are waiting to start treatment until the risk/benefit ratio is acceptable. (D) Drug class cross resistance. (E) Drug interactions (esp NNRTI's and PI's) (F) Logistics and cost of delivering this life-saving therapy to the developing world.
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(MIDII #271)
HERPESVIRUSES => Name four common features of herpesviruses. Discuss latent infection in more detail. |
Common features of herpes viruses are: (1) similar morphology, (2) similar modes of replication, (3) ability to cause a PRIMARY infection followed by a LATENT infection that is lifelong for the host, (4) ubiquitous and found all over the world.
Herpesviruses can replicate in both lytic & latent fashion. During lytic infection, all viral genes are expressed and host cell dies as a result. During latent infection there is limited gene expression, and the host cell survives, in some cases for many years. During latent infection host has no symptoms. Latency can be overcome, leading to lytic infection. HSV-1 causes primary infection in the mouth (gingivostomatitis) followed by latency. Years later the latent (limited gene expression) HSV can reactivate (express all of its genes) to cause a cold sore at the corner of the mouth, which can be painful, annoying, & enables the virus to spread to another person. After primary infection or reactivated latent infection, continuous low grade virus multiplication can rarely occur, often with some symptoms => persistent infection with lytic replication. |
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(MIDII #272)
Do herpesviruses cause reinfections? |
Yes! Immunity to these viruses is often incomplete. Although there is only 1 antigenic type of HSV-1, individuals infected with HSV previously can be reinfected with a slightly different type of HSV-1.
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(MIDII #273)
How many herpesviruses are there which infect humans? Discuss the alpha, beta, and gamma herpesviruses. |
There are 8 known Herpesviruses that infect humans. ALPHAVIRUSES include HSV-1, HSV-2, and varicella-zoster virus (VZV). Short replication cycle, variable host range, become latent in sensory neurons. HSV causes a variety of infections of the skin and mucous membranes, genitalia, and nervous system. VZV causes chickenpox & shingles (zoster). BETAherpesVIRUSES include CMV and Human Herpes Viruses 6 & 7 (HHV 6, HHV 7). Long replication cycle, narrow host range, latent in lymphoid and other cells (salivary glands & kidney). Cause systemic infections that are often asymptomatic in otherwise healthy people. Cause severe infections in the fetus and in immunocompromised pts. GAMMAherpesVIRUSES include EBV and HHV 8 (or Kaposi sarcoma virus: KSV). Narrow host range, become latent in lymphoid cells, and are associated w/tumors. EBV causes infectious mononucleosis and a variety of tumors.
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(MIDII #274)
Discuss transcription of the herpes viral genome! Process is shared by all herpesviruses. |
Replication is associated with expression of viral genes. Progresses as a cascade in 3 stages: immediate early (IE), early (E), and late (L), leading to LYTIC infection. Latency may involve a break that occurs between the 1st and 2nd stages of viral gene expression. IE genes translate proteins that bind DNA and regulate gene expression. E genes encode for transcription factors & enzymes like DNA pol, and thymidine kinase (TK), which are crucial for viral replication. (Enzymes are excellent targets for antiviral therapy!) L genes encode for structural proteins, such as glycoproteins of the virus which form its envelope or coat. Envelope is req'd for infectivity of the virus.
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(MIDII #275)
Describe the morphology of a typical herpesvirus! Pictured in the slide is VZV. |
Composed of a phospho-glycolipid envelope, a tegument, and icosahedral (20-sided) capsid, and a DNA core. VZV, HSV-1, HSV-2, CMV, EBV, all look indistinguishable as seen by electron microscopy. Viral envelope contains glycoproteins (gps) called gB, gC, gE, etc. Appear on the surface of the virion and on the surface of the infected host cell. Play an impt role in spreading infection from one cell to another and are a significant target for host immunity. Herpesviruses can spread in 2 ways, as the free enveloped particle and also from cell-to-cell. For later spread, cellular immunity is critical in host defense. Abs cannot reach viruses multiplying within cells. Herpesviruses use a LOT of cell-to-cell spread, which is why cellular immunity is critical for host defense against this virus. The TEGUMENT contains ORFs (open reading frame proteins) #'s 4, 10, 21, 62, and 63. ORF 62 is an impt IE gene, critical for new virus formation and a lynchpin for VZV synthesis.
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(MIDII #276)
Describe the organization of the VZV genome. |
Divided into unique long and short sequences which contain internal and external repeats. U = unique, L = long, S = short, T = terminal, R = repeat.
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(MIDII #277)
What are the receptors for Varicella Zoster Virus (VZV)? Is VZV released extracellularly in infectious form? Can it spread from cell-to-cell in an infected host? What form of immunity, cellular or Ab-mediated, is most effective against VZV infection? |
VZV receptors are heparan sulfate & mannose 6 phosphate receptor (MPR). Newly synthesized cellular proteins are sorted from exit from cells at the Golgi complex. Mannose 6 phosphate receptors are normally present in human cells of the trans-Golgi network and cell surface and play a role in the sorting of some cellular proteins into endosomes or lysosomes. VZV follows this pathway during egress because its envelope contains mannose-6-phosphate. Since the gps of VZV contain M-6-P, the virions are incorporated into endosomes, where they are inactivated by the acid environment and are not released extracellularly in infectious form. Virus spreads only from cell-to-cell in the infected host. So VZV must be attacked with a cell-mediated response; an Ab response is not helpful.
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(MIDII #278)
Where is herpesvirus formed in an infected cell? |
DNA replicates in the nucleus. Nucleocapsids are formed there. Extruded into the perinuclear space. Env is seen surrounding the capside but is NOT final envelope. Nucleocapsid w/early env progresses to the cytosol where it is extruded as its envelope is fused with the RER, releasing the naked nucleocapsid into the cytosol. Glycoproteins are made in the RER and transported to the Golgi. Tegument proteins are also made in the cytosol and transported to the Golgi. In the trans-Golgi network (TGN), due to the processes of protein signaling, capsid, tegument, and glycoproteins come together. Nucleocapsids are then enveloped by tegument proteins and glycoproteins, leading to enveloped virions.
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(MIDII #279)
(1) What are the receptors for herpes simplex virus (HSV) and what is their role in pathogenesis of HSV infection? (2) What glycoproteins on the cell surface of HSV enable it to attach to host cells and infect them? (3) Can HSV be released extracellularly in infectious form? What is the primary form of host defense against HSV infection: Ab-mediated or cellular? |
(1)Enveloped viral particles invade cells by utilizing receptors on the cell surface. Receptors for HSV include heparin sulfate, and Hve A-C and Nectin-1 and -2, which are members of the immunoglobulin and TNF families. (2) Gps B, D, H, & L on the virion enable HSV to attach to cells and infect them. These gps are also present on the surface of infected cells and facilitate cell-to-cell spread of HSV, utilizing the same gps to attach to the cell and invade it. Glycoprotein D is the major gp of HSV; (VZV lacks GpD and uses GpE instead.) (3) HSV has an unknown means by which it is able to evade endosomes and so it is released extracellularly in infectious form. Although the primary form of the host defense against HSV is cellular immunity, Abs play more of a role in defense than for VZV.
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(MIDII #280)
What is the result of lytic infection with HSV? Latent infection? |
Lytic infection with HSV results in cell death. Latent infection allows cell to live unless reactivation occurs, at which point the cell dies. Latency for HSV is different from VZV. With HSV there is a very limited repertoire of gene expression, with only a few latency associated transcripts (LATs) expressed, and no protein expression. There is minimal transcription of DNA and no translation of proteins in latency of HSV.
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(MIDII #281)
Discuss classification of HSV infections. |
Primary, non-primary, first episode, recurrent, & reinfection. Many HSV infections are asymptomatic. (a) PRIMARY HSV-1 infection is very common, occurs in 1st few years of life, may be symptomatic (gingivostomatitis) or asymptomatic. (b) PRIMARY genital HSV-2 infection is less universal than HSV-1 infection. Occurs after 1st decade of life when sexual activity begins. Can be transmitted from a pregnant woman to her baby, seen in newborn infants, in whom it is severe or fatal if untreated. (c) NON-PRIMARY infection is defined as 1st infection w/one HSV in setting of past infection w/other. HSV-2 infection in someone already infected w/HSV-1. Non-primary infections tend to be milder than primary infections. (d) FIRST EPISODE DISEASE is when an individual has a 1st HSV infection that is asymptomatic, but then develops a symptomatic infection, either due to reactivation of the 1st HSV, or reinfection w/a new one. (e) RECURRENT INFECTIONS are due to reactivation of latent infection. HSV-1: painful ulcers or vesicles at corners of the mouth. For HSV-1, infections usually occur above the belt on the face or trunk. For HSV-2, commonly below the belt. Genital HSV-2 may also be primary, non-primary, first episode or recurrent.
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(MIDII #282)
(1)What provokes recurrent HSV infections? (2) Are HSV infections always symptomatic? (3) What host factors determine the severity of HSV infections? |
(1)Recurrent HSV infections are provoked by fever, trauma, sunlight, stress, & menstruation. Reactivation occurs despite presence of specific Abs. May be related to deficient IFN-γ. Severing CN V reactivates latent HSV-1 in humans and animals. NOTE: A RECURRENT vesicular rash in the same area of skin (usually face) is diagnostic of reactivation of HSV (NOT VZV). (2) Many HSV infections are asymptomatic. Infectious virus is still produced and is “shed.” 3% of healthy adults shed HSV-1 with no symptoms. Individuals shedding virus are infectious. Asymptomatic shedding is the major means by which HSV 2 is spread sexually. (3) Host factors are very impt in whether HSV infections are severe. Cell-mediated immune response is critical. Severe infections are seen in immunocompromised pts, newborn babies (w/immature cell-mediated immunity). Pts receiving chemo or radiation therapy for cancer, transplant pts, pts on high dose steroids, pts w/HIV, pts born w/immunodeficiency diseases, particularly those w/congenital defects in cell-mediated immunity.
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(MIDII #283)
HSV 1 and/or 2 cause a variety of infections which can affect skin and/or mucous membranes, occur in neonates, and involve the CNS. Discuss. |
(A) HSV-1: gingivostomatitis, whitlow of the finger, keratitis (infection of the cornea of the eye), encephalitis, and severe infection of the skin in people with underlying eczema (eczema herpeticum). Neonatal infection with HSV-1 occurs but is unusual. (B) HSV-2: genital infection sometimes accompanied by meningitis (during primary infection), and neonatal infection. HSV-2 can be passed from mother to child in the birth canal and causes severe infection in the newborn. Disease is due to presence of virus growing in cells and also from the immune response to the virus.
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(MIDII #284)
HSV-1 => GINGIVOSTOMATITIS |
Baby with primary HSV-1 gingivostomatitis. Ulcers on the oral mucosa, along with swollen and friable gums. Secondary infection on the thumb from sucking on it. Satellite lesions on the surrounding skin. Looks very severe but is a self-limited infection. Poor nutrition and dehydration for a few days can be a problem. Primary infection can be asymptomatic but recurrent disease (fever blisters) are symptomatic. Painful but causes limited problems. Patients are usually not treated w/antiviral meds. (It is customary to treat pts in whom genital HSV 2 is diagnosed. HSV 2 commonly recurs, more often than HSV 1).
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(MIDII #285)
HSV-1 => HERPETIC WHITLOW |
Lesions are painful and extremely infectious to others. Punctures of these sores produces watery fluid from which HSV can be cultured. Infected fingertips, looks like a staph infection.
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(MIDII #286)
Which form of herpes causes encephalitis? Is it treatable? |
HSV 1 is the cause of the most common form of focal encephalitis in US. Symptoms/signs include headache, personality change, focal seizures, abnormal EEG, CT, MR. Personality change is caused by pathological involvement of the temporal lobe. Radiological findings are not useful for early dx of HSV infection, appear late in the course of infection. DDx for pt with these symptoms includes other infections as well as tumors. Dx is best accomplished by performing PCR on CSF. Rare to isolate HSV from CSF in encephalitis. If HSV 1 encephalitis is strongly suspected, antiviral treatment is usually begun before result of PCR is known. Best prognosis is in children (not adults) who are treated soon after disease onset. Adults may survive, but with neurological deficits. HSV-1 is one of the few forms of treatable encephalitis.
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(MIDII #287)
Discuss perinatal HSV infection. Is this caused by HSV-1 or -2? |
Perinatal HSV can be severe or fatal. Usually due to HSV-2. Baby is infected from contact w/mom's infected genital tissues and secretions if she has genital HSV at the time of delivery. Mom has no symptoms of genital infection. Attack rate is >10 times greater in maternal primary infection compared to recurrence. Mom who is newly infected near time of birth is 10 times more likely to pass on HSV 2 to her infant when giving birth vaginally. Women with obvious vaginal HSV at delivery usually have a cesarean section to protect baby from infection. SIGNS: skin vesicles, fever, seizures, pneumonia, DIC, and conjunctivitis. Spectrum ranges from apparently mild to very severe. Therapy is aimed at preventing mild disease from progressing to severe disease. Dx is made by testing skin lesions and/or CSF for HSV 2 by culture, for virus, immunofluorescence, & PCR. Infant should be treated with antiviral therapy even if he/she is asymptomatic if at risk (has only skin vesicles). May be life-saving for the infant. Late treatment or untreated disease has a VERY poor prognosis for the infant: retardation or death.
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(MIDII #288)
Can a baby be diagnosed with HSV 1? If so, would you treat such a baby with antivirals? What is the prognosis? |
Baby kissed by mom with undiagnosed HSV-1 kissed the newborn after birth and gave the baby HSV-1 infection. Prompt diagnosis and treatment result in a normal baby. Prognosis of neonatal HSV-1 is better than that of HSV-2 because HSV-1 is more sensitive to antiviral therapy than HSV 2.
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(MIDII #289)
What are the 3 clinical categories of neonatal HSV infection? How do we diagnose these babies? |
Diagnosis: immunofluorescence, culture, PCR. Abs in mom and babe isn't useful b/c it takes too long and may not yield useful data. Impt to begin antiviral therapy ASAP for best outcome. Recurrent skin vesicles in the baby are associated w/poorer prognosis. 3 CLINICAL CATEGORIES =>(1) Skin and mucous membrane infection only (40% of HSV infected babies). No symptoms other than skin rash (grouped vesicles). Excellent prognosis with early therapy, keeps virus from spreading. Possible to dx these infections easily, virus produces skin lesions from which it can be ID'd. (2) CNS infection (35% of infected babies): fever, lethargy, seizures. CSF is abnormal. Babies have major sequelae if they survive. Diseas is hard to diagnose b/c don't usually have skin vesicles. (3) Disseminated disease (25% of infected babies): 2/3 develop skin vesicles but the 1/3 who don't are hard to diagnose. Hepatosplenomegaly, jaundice, hepatitis, pneumonia. Mortality is very high (70%).
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(MIDII #290)
Varicella-Zoster Virus (VZV): Primary vs. Secondary Infection. Is there asymptomatic shedding of VZV? |
PRIMARY: Varicella is a highly contagious disease, spread by airborne route. Complications: bacterial superinfection, encephalitis, pneumonia, congenital syndrome. A young boy w/classic chickenpox is not very ill, has skin vesicles characteristic of varicella. Vesicles are full of infectious virus. Enveloped virions are produced in the body here (otherwise cell-to-cell spread through the body is the rule.) Virions can be aerosolized, so disease spreads by airborne route from the skin. SECONDARY: Zoster is due to reactivation of latent VZV. Zoster occurs when the cell-mediated immune response to VZV is low. There is NO asymptomatic shedding of VZV. Zoster is infectious only when it is clinically apparent. When zoster spreads VZV to others, they develop chickenpox, not shingles. Classically the rash is on one side of the body, stops abruptly at the midline. Distribution of the rash reflects the pathogenesis of the illness. Zoster ONLY occurs in ppl who had chickenpox (varicella) previously.
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(MIDII #291)
PATHOGENESIS of Varicella |
Virions infect respiratory mucosa and spread to T lymphocytes (viremia) where virus is not accessible to Abs. Virus spreads slowly from cell-to-cell. Incubation period of 2-3 wks. Slow spread keeps virus from overwhelming the host. Immune system develops cell-mediated response that can control the virus. Immunocompromised pts are deficient in this response and can develop severe or fatal varicella if untreated. This long incubation period is why the varicella vaccine works so well.
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(MIDII #292)
Describe CONGENITAL VARICELLA |
Infant's mom had varicella during pregnancy. Intrauterine immune response to virus was immature, resulting in fetal infection and poorly checked viral replication. Led to overwhelming latent infection. Baby died before age 1. Rare outcome of maternal infection.
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(MIDII #293)
Can a baby develop ZOSTER (shingles)? |
3 month old baby with classic zoster. Baby's mom had varicella during pregnancy and the baby developed latent infection. Virus reactivated at an early age and produced this illness.
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(MIDII #294)
What happens when varicella or zoster occurs in an immunocompromised patient? How can we avert this? |
Severe, even fatal. When an immunocompromised susceptible is exposed to someone w/a VZV infection, severe infection can be averted by passive immunization, providing specific Abs to modify an infection. VZIG must be given as soon as possible after exposure to work. Only useful when given to a susceptible. Will not prevent reinfection and will not prevent zoster. People given VZIG either develop no varicella or only a mild case. Often, immunocompromised pts will not know they have been exposed to VZV and will present with full blown varicella. Impt to treat them with antiviral meds ASAP. Immunocompromised pts who have had chickenpox are at increased risk to develop zoster (shingles). Should receive antiviral therapy. Due to defects in cell-mediated immunity. More likely to develop a poorly understood pain syndrome following zoster: post herpetic neuralgia (PHN). Pts over age 50 are also at risk to develop zoster and PHN.
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(MIDII #295)
Discuss pathogenesis of latent VZV infection and ZOSTER. |
During varicella the virions are present on skin and can invade sensory neurons without multiplying (which would kill the neuron). Virus becomes latent. In latency it expresses 6 of 68 genes, but cascade of lytic infection is blocked. Subsequently the virus reactivates in 15% of ppl who have had varicella. 6 regulatory proteins (from IE and E genes) are expressed. In lytic infection this expression is nuclear but in latent infection it is cytoplasmic. Cascade of gene expression is blocked b/c regulatory proteins are excluded from the nucleus in VZV latency. For latent infection to occur, cell free, enveloped virus must be able to infect neurons. Latent VZV infection only occurs in neurons.
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(MIDII #296)
Is there a vaccine for any of the herpesviruses? |
VZV is the only herpesvirus with a vaccine. Live attenuated strain (Oka) of VZV. Licensed for routine use in healthy persons. Very safe. Given to 4 million American children annually. Incidence of varicella has decreased in all age groups, including herd immunity. Very few contraindications to varicella vaccine: being pregnant, being allergic to the vaccine components, and being immunocompromised. The vaccine causes a mild rash 1 month after vaccination in 5% of those immunized. Spread of vaccine virus from skin lesions is rare and not harmful. No vaccine is 100% effective or 100% safe. Varicella vaccine protects 85% of people from any form of disease. The remainder develop mild illness. Immunity does not wane with time after vaccination. Zoster after vaccination is rare because virus rarely reaches the skin to cause latent infection.
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(MIDII #297)
How do we diagnose HSV and VZV? |
Culture, direct immunofluorescence (DFA), and PCR on smears from a skin rash. Positive cultures for HSV can develop within 24-48 hrs. VZV is more difficult to culture, results take 5-7 days. A raise in Ab titer is also diagnostic of infection. Performed on acute (at disease onset) and convalescent (10-14 days after onset) serum specimens, measuring specific IgG Abs. A positive titer of specific IgM is an indication of acute infection.
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(MIDII #298)
Discuss antiviral treatment for HSV and VZV. |
Acyclovir is used most commonly. Interferes w/viral DNA synthesis. MOA: depends on viral thymidine kinase (TK) and DNA pol (E genes). Non-toxic, well-tolerated in pts. HSV-1, HSV-2, and VZV are sensitive to ACV. (VZV is < sensitive than HSV, and HSV1 > sensitive than HSV2.) Pts w/VZV are treated with higher doses of ACV than HSV pts. EBV and CMV are NOT sensitive to acyclovir. ACV can be given orally or IV. Adverse effects are unusual: GI symptoms in 20%, neurologic symptoms in 5% (headache, anxiety, seizures, delirum) are most common. Bone marrow suppression (anemia, low platelets) is associated with long-term, high dose use. Herpesviruses can become resistant to ACV by ceasing to make Tk. Newer drugs (Famciclovir, Valacyclovir) are administered only orally, converted to ACV in the body. High absorption in the GI tract, result in higher blood levels of ACV than can be achieved by giving ACV orally. Mainly used to treat pts with genital HSV 2 and elderly pts with zoster.
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(MIDII #299)
CYTOMEGALOVIRUS (CMV) => Morphology and General Description |
CMV is the largest of the human herpesviruses! 208 ORFs (compared to 68 w/VZV). Major gps are gB and gH. Breaks rules as a DNA virus – has an mRNA in its genome. Has genes that down-regulate expression of class I MHC, interfering w/activity of cytotoxic lymphocytes (CTLs). Virus is immunosuppressive. Host defense depends on cellular immunity. Virus poses risks to fetus and immunocompromised pts. CMV becomes latent in bone marrow precursors of monocytes. Cells differentiate into MΦ's when stimulated by Ags, reactivating their latent CMV. CMV is a significant threat to pts who have undergone transplantation, after which significant immune activation occurs. Reactivation of CMV can occur in transplant recipient and transplanted organ.
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(MIDII #300)
What does CMV infection look like in a healthy adult host? In an immunocompromised host? In a pregnant woman? |
Subclinical! A rare mononucleosis-like syndrome is attributed to CMV. Self-limited. Severe CMV infections occur in immunocompromised hosts. When pregnant women are infected w/CMV, their fetus may be infected. Because of immaturity of the fetal immune system, the fetus may develop congenital CMV infection. Can be severe or fatal. When a baby acquires CMV infection at birth, from contact from infected maternal secretions, the infection is innocuous. Babies infected with CMV by breast feeding are not significantly affected by this virus.
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(MIDII #301)
What is the most common cause of congenital viral infection in the US? |
CMV causes 40,000 annual courses. 3000 of these infected babies will have symptoms at birth such as: prematurity, jaundice, microcephaly, rash. Poor prognosis. 8000 will appear normal at birth but will develop deafness and mild retardation as they grow older. Risk to infant is highest when mom is infected in the first trimester. Reinfection is common but it is rare for an infected woman who is reinfected w/CMV during pregnancy to have a significantly affected infant. Useful to distinguish between congenital and perinatal infection (at birth, inconsequential). Culture urine from baby for the first 3 wks of life. Not done. No good therapy for infants with significant clinical CMV.
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(MIDII #302)
Discuss CMV infections in immunocompromised pts. |
Frequent, may be severe. May be primary, recurrent, due to reactivation from latency. Many strains of CMV. 1 antigenic type. Reinfections are common. Symptoms and signs: fever, pneumonia, retinitis, colitis, lymphadenopathy, rash, encephalitis, neutropenia. Dx can be tough. Virus can be easily demonstrated in body tissues or fluids, by culture or PCR, but it's necessary to distinguish actual disease from persistent low grade viral multiplication which may be innocuous. Asymptomatic CMV infections may occur in immunocompromised pts. With use of protease inhibitors to treat HIV pts, CMV infections have become less severe b/c pts are less immune compromised.
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(MIDII #303)
Discuss treatment of CMV. |
Cannot be treated with ACV. Require use of more toxic drugs: ganciclovir, foscarnet, cidofovir. Meds must be given IV, cause more toxicity than ACV. Bone marrow suppression, metabolic irregularities. Accurate diagnosis is very impt b/c drugs are toxic. Most of treatment of CMV disease is in immunocompromised pts w/very significant illnesses. The drugs that treat CMV act by inhibiting viral DNA polymerase. GANCICLOVIR is related to ACV, but more toxic => bone marrow suppression. So frequent and severe that treatment must be discontinued in 20% of pts who receive it. Still, ganciclovir is the drug of choice to treat CMV infections. FOSCARNET toxicity includes renal damage, metabolic abnormalities. CIDOFOVIR toxicity includes renal damage and increases in uric acid. Because of its toxicity, cidofovir is rarely used.
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(MIDII #304)
Discuss transmission of CMV. |
Associated w/close personal contact. Transmission can be sexual: saliva, tears, and urine contain infectious CMV. Virus can persist on surfaces for periods long enough to transmit to others. Children in daycare transmit CMV to others via their infected saliva and urine. For other children this transmission is inconsquential but when they transmit CMV to susceptible adults who may be pregnant there can be serious consequences. CMV is rarely airborne, highly cell-associated and does not produce skin lesions. So transmission from infected pts to hospital workers is rare. Intrauterine transmission of CMV occurs, as well as infection through breast milk. CMV may be transmitted through blood transfusions and organ transplantation.
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(MIDII #305)
How do we prevent transmission of CMV? |
Proper handwashing after examining pts and diapering infants. Use of condoms can prevent sexual CMV transmission. For high risk pts: transplant pts are tested before transplantation and the donor is also tested. Greatest risk is when person transplanted is CMV Ab neg and the donor is CMV Ab positive. Lesser risks when recipient is CMV Ab positive. All transplant patients are at substantial risk from CMV. Also useful to test blood for CMV positivity prior to transfusion. Optimally, CMV seronegative blood is safest for transfusion of immunocompromised pts. CMV positive blood may be irradiated or filtered to remove infectious CMV.
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(MIDII #306)
Epstein Barr Virus (EBV) => General Description |
Member of herpesvirus family, GAMMA herpes virus. Can cause lytic, latent, and immortalizing infections. Causes infectious mononucleosis. Major gp is gp 350, which binds to CD21 (the C3d complement receptor) on B lymphocytes. Pts w/x-linked agammaglobulinemia cannot be infected w/EBV. Seropositive asymptomatic individuals shed virus in their saliva and can infect others. Lytic infection w/EBV in the body of immunocompetent pts. EBV is capable of immune evasion. Carries genes that mimic IL-10, decrease IFN production, and inhibit apoptosis. There is no good treatment for EBV infections. Experimental approaches include: decreasing immunosuppressive therapy, giving monoclonal Abs (Rituximab), and infusion of immune lymphocytes.
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(MIDII #307)
In addition to infectious mononucleosis, what else can EBV cause? |
Nasopharyngeal carcinoma, lymphomas (including Burkitt's), oral hairy leukoplakia in AIDS pts, and the x-linked lymphoproliferative syndrome (only in male pts).
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(MIDII #308)
Discuss Infectious Mononucleosis (caused by EBV). |
B lymphocytes are latently infected w/EBV. Cells form a variety of Abs, called heterophile. Normal immune response is mediated by cytotoxic T lymphocytes, seen as “atypical lymphocytes” on blood smears. Latent EBV persists in memory B cells. No treatment for EBV, but steroid therapy has been used to treat complications such as airway obstruction due to enlarged lymph nodes, hemolytic anemia, and very severe cardiac and neurologic complications. IM usually occurs in young adults. Signs/symptoms include fever, lymphadenopathy, exudative pharyngitis, hepatosplenomegaly, and fatigue. (If treated w/ampicillin will develop a characteristic maculopapular rash). Monospot test for heterophile Abs can provide tentative dx. Definitive dx is made by demonstration of specific Abs. Abs to viral capsid antigen (ACA) develop early in IM and persist for life. Abs to EBNA (EBV nuclear antigen) develop late and also persist for life. Blood positive for anti-VCA and neg for anti-EBNA is diagnostic of acute mono.
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(MIDII #309)
Discuss the beta human herpes viruses 6 and 7. |
(A) HHV-6 causes acute roseola in infants. Babies present with irritability and high fevers that may cause seizures. As fever falls, a maculopapular rash occurs. For most babies, self-limited illness. High fevers in small babies are always a cause for concern because might indicate serious causes of infection. Are there long term sequelae of HHV-6 following roseola? It becomes latent in the CNS, but we don't know. HHV-6 also causes fever in immunocompromised persons and a rare IM-like syndrome. (B) HHV-7 causes fevers in immunocompromised pts. (Treatment) These infections don't require specific treatment, most are self-limited.
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(MIDII #310)
Discuss HHV-8. |
Closely related to EBV. Gamma herpesvirus. Large virus. Encodes its own genes and has pirated a number of human genes including IL-6, Bcl-2 (anti-apoptosis), and genes encoding chemokines. Infections in children with this virus are rare but include a non-specific rash illness. This virus causes Kaposi's Sarcoma in HIV pts and in the elderly. Also causes a primary-effusion lymphoma and Castleman's disease. No effective antiviral therapy.
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(MIDII #311)
Definitions => ENCEPHALITIS (viral encephalitis) |
Encephalitis refers to inflammation of the brain, which should be distinguished from meningitis, inflammation of the meninges. Viral cncephalitis is characterized by acute fever, headache, and evidence of parenchymal brain involvement such as changes in mental status and seizures. Unlike viral meningitis, which is benign and self-limited, viral encephalitis is associated with substantial morbidity and mortality. Symptoms include fever, headache, altered mental status, decreased consciousness, and focal neurological signs & symptoms including seizures, weakness, and speech disturbances. Typical CSF findings are similar to those found in viral meningitis. The most common causes of viral encephalitis in the US are HSV-1, arboviruses, and enteroviruses.
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(MIDII #312)
Definitions => VIRAL MENINGITIS (aseptic meningitis) |
Viral meningitis is an infection of the subarachnoid space caused by a virus. Predominant clinical features of fever, headache, and nuchal rigidity (neck stiffness) are often accompanied by nausea, vomiting, and malaise. Viral meningitis is usually a self-limited illness which lasts 7-10 days. Can be caused by enteroviruses (by far the most common cause), arboviruses (usually cause encephalitis), herpesviruses (HSV-2 causes meningitis, HSV-1 causes encephalitis), acute HIV infection, and mumps. Typical CSF findings include mild to moderate lymphocytic pleocytosis (elevated WBC count comprised mostly of lymphocytes, usually 10-500 WBCs/mm^3), normal or slightly elevated protein Cx (<100 mg/dl), and a normal glucose Cx. Different from bacterial meningitis w/neutrophilic pleocytosis (>1000 WBCs/mm^3, >80% of which are PMNs), protein >100 mg/dl, and glucose <40 mg/dl. NOTE: Early during the course of viral meningitis, a neutrophilic pleocytosis may occur which evolves within one day to a lymphocytic pleocytosis.
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(MIDII #313)
What is MENINGOENCEPHALITIS? |
Meningitis and encephalitis do not always occur exclusively. The term meningoencephalitis refers to inflammation of the meninges and brain parenchyma. Impt to note presence of altered mental status or focal neurological signs or symptoms should prompt one to consider encephalitis or meningoencephalitis, as opposed to a pure meningitis, in the DDx. Raises possibility of different etiologies or treatment.
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(MIDII #314)
What is MYELITIS? |
Inflammation of the spinal cord, which can cause symptoms of weakness, paralysis, sensory loss, and bowel and bladder disturbances. Poliomyelitis is the classic example of viral myelitis, but other causes include nonpolio enteroviruses, herpesviruses, retroviruses, and West Nile virus. Meningitis, encephalitis, and myelitis may all occur together during an infection which would be described a MENINGOENCEPHALOMYELITIS.
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(MIDII #315)
CSF Findings in Selected CNS Infections |
(1) NORMAL: WBC Count => 0-5 WBC/mm^3; Cell type => Lymphocytes; Glucose => 50-75 mg/dL; Protein => 15-40 mg/dL.
(2) BACTERIAL MENINGITIS: WBCs => 100-10,000; Cells => >80% PMNs ; Glucose => <40; Protein => 100-1000 (3) VIRAL MENINGITIS/ENCEPHALITIS: WBCs=> 10-500; Cells => Lymph (early PMNs); Glucose => normal 50-75; Protein => 50-100 (slightly elevated). (4) TB MENINGITIS: WBCs => <500; Cells => Lymph; Glucose => <50; Protein => 100-300 (moderately elevated). (5) CRYPTOCOCCAL MENINGITIS: WBCs => 10-200; Cells => Lymph; Glucose => <40; Protein => 50-300. |
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(MIDII #316)
Discuss the Epidemiology of Viral Encephalitis |
Japanese encephalitis virus is the most common cause of viral encephalitis worldwide. HSV-1 is the most common cause of sporadic viral encephalitis in the US. Arbovirus infections (caused by the bite of a mosquito) tend to occur in the summer in temperate climates, while HSV-1 infections occur year round. Infection with virus leads most commonly to a subclinical infection; only a small chance of development of encephalitis. Chance of encephalitis is greater in the very young, the elderly, and the immunocompromised. Widespread vaccination against measles and polio has reduced occurrence of encephalitis and myelitis due to these agents, but in countries where vaccination isn't as successful, we still see them.
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(MIDII #317)
Distinguish between neurotropism, neuroinvasiveness, and neurovirulence, and discuss these characteristics of Rabies virus, HSV, and Mumps. |
(1)NEUROTROPISM: ability of virus to infect neural cells. (2) NEUROINVASIVENESS: ability of a virus to enter the CNS. (3) NEUROVIRULENCE: ability of a virus to cause disease of nervous tissue once it enters the CNS. (4) Rabies virus => high neuroinvasiveness & high neurovirulence, readily spreads to the CNS causing 100% mortality in the absence of early treatment. (5) HSV => low neuroinvasiveness, but high neurovirulence, always enters the PNS but rarely enters the CNS. Leads to severe consequences when it does enter the CNS. (6) Mumps virus has high neuroinvasiveness but low neurovirulence; often invades the CNS, but neurological disease is mild.
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(MIDII #318)
Will infection with a neurotropic virus always cause encephalitis? Will it cause encephalitis in every host? |
Outcome of infection with a neurotropic virus depends on several factors, including: neuroinvasiveness and neurovirulence of the virus, site of entry, size of inoculum, and host factors including age, sex, immune status, and genetic factors. The same exposure to, say, St. Louis encephalitis virus could cause subclinical infection (person is not sick) in a 25 year old or fatal encephalitis in a 70 year old.
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(MIDII #319)
Discuss pathogenesis of viral encephalitis. |
Neurotropic viruses must enter the host to cause disease. Entry via respiratory tract (measles, VZV), the GI tract (enteroviruses), the genitourinary tract (HIV), the skin/subcutaneous tissue (arboviruses), ocular conjunctiva (enterovirus 70), and direct inoculation into the blood (transfusion-associated HIV or CMV). Once entry has occurred, pathways used to initiate systemic invasion are incompletely understood but may involve adherence to M cells and transport across M cells to underlying lymphoid tissue from whence hematogenous or neural spread can occur. Hematogenous and neural dissemination are the primary mechanisms by which neurotropic viruses enter the CNS.
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(MIDII #320)
Discuss HEMATOGENOUS SPREAD of neutrotropic viruses into the CNS. |
Viruses may travel in the blood free in the plasma, in association w/cells, or both. BBB is composed of TJ's between brain capillary endothelial cells, and the separation of these cells from brain parenchyma is by a dense BM. Breaching of BBB can occur by a variety of mechanisms: (1) Virus may invade CNS at sites where capillary endothelial cells are not joined by TJ's and the BM is thin – like the choroid plexus. Infection of choroid plexus epithelial cells leads to entry of virus into ventricular CSF and then into ependymal cells lining the ventricles and the subependymal tissues. (2) Virus may directly infect cerebral capillary endothelial cells and then spread into the surrounding brain tissue. (3) Virus may infect and be transported within circulatory cells (including monocytes, MΦs, PMNs, lymphocytes) which subsequently enter the CNS via diapedesis, bringing virus with them.
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(MIDII #321)
Discuss NEURAL SPREAD of neurotropic viruses into the CNS. |
Many neural cells within the CNS (motor neurons of the spinal cord, olfactory neurons) have processes that extend outside the BBB, and so axoplasmic transport within these neurons can deliver viruses directly into the CNS. Spread within neurons is primary mode of CNS infection for rabies virus and HSV. Rabies virus enters motor neuron axons at the neuromuscular junction (NMJ) (where it replicates in muscle after being inoculated via a bite). Is transported retrograde directly into the CNS. HSV achieves latency in the DRG. Upon reactivation can be neurally transported anterograde to the sin leading to vesicular skin lesions or retrograde to the CNS to cause encephalitis. Neurotropic viruses which enter the host via the GI tract can infect neurons in the myenteric plexus and be transported into the CNS via the vagus nerve.
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(MIDII #322)
Discuss NEUROVIRULENCE of viruses that enter the CNS. |
Once inside the CNS, many neurotropic viruses infect the neurons. Outcome of infection can be latency, subtly altered cellular functions, or cell death via apoptosis or necrosis. Cell death via necrosis involves disruption of cytoplasmic membrane integrity w/subsequent release of intracellular proteins and an inflamm response. Clinical manifestations of neuronal death or dysfunction depend on anatomic location (cortical infection leading to change in neurocognitive functioning; brainstem infection leading to coma and respiratory failure). Less commonly, oligodendroglial cells may be infected as in JC virus infection which, reactivated in immunosuppressed individuals, leads to demyelination and PML (progressive multifocal leukoencephalopathy).
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(MIDII #323)
Discuss IMMUNOPATHOLOGY of viral infection of the CNS |
Much of the pathology caused by viral infection may be caused by host immune response to the viral infection. During severe encephalitis, an inflammatory rxn is usually present in the meninges and in a perivascular distribution in the brain. Is this protective (clearing virus and virally-infected cells) or pathologic (releasing pro-inflamm cytokines that contribute to neuronal dysfunction & death)? Not clear.
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(MIDII #324)
Discuss postviral encephalomyelitis. |
The brain (spinal cord and peripheral nerves) can also be affected by postinfectious demyelinating processes that don't involve direct invasion of brain w/etiologic agent. Acute disseminated encephalomyelitis (ADM) is a CNS illness in which demyelination occurs after infection w/a virus, usually following systemic illness by days or wks. Clinical manifestations can be tough to differentiate from encephalitis caused by direct viral invasion. Pathogenesis is due to induction of an immune response to CNS myelin. Systemic infection with meales, varicella, and influenza A have been associated with postviral encephalomyelitis.
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(MIDII #325)
VIRAL ENCEPHALITIS => Clinical Manifestations |
Headache, fever, alterations of consciousness (lethargy to coma), confusion, cognitive impairment, personality changes, motor weakness, seizures, movement disorders, accentuated deep tendon reflexes, extensor plantar responses. Increased intracranial pressure can occur, papilledema, cranial nerve palsies, and progression to coma. Viral encephalitis is usually an acute illness, with or without a prodrome, but can also be a slowly progressive disease as in progressive multifocal encephalopathy (PML) caused by JC virus, subacute sclerosing panencephalitis (SSPE) occurring after measles, and HIV encephalopathy.
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(MIDII #326)
VIRAL ENCEPHALITIS => Diagnosis |
Hx: inquire about insect or animal bites, recent travel, sexual exposures, immunization status. Look for signs of systemic illness - rashes, lymphadenopathy; meningismus (stiff neck); decreased level of consciousness; focal neurologic signs (weakness, speech abnormalities, increased tone, plantar extensor reflexes). Most impt lab eval is the CSF profile. RBCs in CSF may occur in HSV-1 encephalitis. Bacterial, fungal, paraistic, or treponemal (syphilis) causes should be ruled out. Search for specific viral etiologies can occur with cultures (of CSF, other fluids), serology (CSF and serum), and detection (in CSF > serum) of viral nucleic acid by PCR. CT scans are performed to establish safety of a lumbar puncture when elevated intracranial pressure is suspected, or to rule out other causes like brain abscess. MRI may reveal focal areas of edema or enhancement, should be performed early. EEG is often abnormal in acute viral encephalitis, with diffuse slowing.
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(MIDII #327)
VIRAL ENCEPHALITIS => Treatment |
Treatment is often supportive: management of increased intracranial pressure, treatment of seizures, management of metabolic derangements. ***Most important point about treatment is that HSV encephalitis responds well to treatment with intravenous acyclovir.*** So pts presenting w/syndrome consistent with encephalitis should be treated empirically with acyclovir for possibility of HSV encephalitis, until HSV is ruled out or another etiology is confirmed.
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(MIDII #328)
CLINICAL VIGNETTE: A 50 year old previously healthy man who lives in Riverdale awakens from a nap that he was uncharacteristically taking on a Saturday afternoon in December, puts on his swimsuit, and begins to fill his bathtub with shredded pieces of that day's newspaper. Although he doesn't find anything odd about his behavior, he does complain of a headache which allows his wife to convince him to go to the ER, where he is found to have a temp of 102.4 and extreme lethargy. |
What do you suspect? Encephalitis. At this point we don't know if it's viral, bacterial, fungal, HIV-caused...could be anything at this point. But since it is in December, you know it's not caused by an arbovirus. Could be HSV-1, the most common cause. Could be an enterovirus. What is it actually? HSV-1 Encephalitis.
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(MIDII #329)
HSV Encephalitis => EPIDEMIOLOGY |
HSV encephalitis is the major treatable viral encephalitis. Most common cause in the US of sporadic, fatal encephalitis with 1000 to 2000 cases occurring annually in the US. Nearly always (96%) caused by HSV-1 as opposed to HSV-2, which typically produces aseptic meningitis but may cause encephalitis in neonates with disseminated disease, in which cases may spread to CNS may be hematogenous. HSV encephalitis occurs in children and adults, year round.
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(MIDII #330)
HSV Encephalitis => PATHOGENESIS |
Proposed entry into the CNS involves retrograde transport of virus via olfactory or trigeminal nerves. In the CNS it replicates in both neurons and glia, causing necrotizing encephalitis and widespread hemorrhagic necrosis throughout the brain parenchyma, but particularly the temporal lobe. HSV encephalitis can occur as a result of reactivation from latency (½ – 2/3) or during primary infection (1/3 – ½). It is more commonly associated with reactivation in older patients, and primary infection in the younger population.
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(MIDII #331)
HSV ENCEPHALITIS => Clinical Features |
Fever, headache, altered consciousness (lethargy to coma), disorientation, personality changes, focal weakness, altered speech, cranial nerve abnormalities, and seizures. Personality changes and bizarre behavior specifically are suggestive of HSV encephalitis and are due to temporal lobe involvement. Onset is sudden, without a prodrome. Characteristic CSF findings as previously discussed for viral encephalitis, but presence of RBCs in the CSF, indicative of hemorrhagic nature of this encephalitis, is suggestive, but not diagnostic of HSV encephalitis. MRI which may be normal early in the course, may reveal temporal lobe edema or enhancement, hemorrhage, or mass effect. EEG may reveal abnormalities specifically localized to the temporal lobe.
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(MIDII #332)
HSV ENCEPHALITIS => Diagnosis |
Dx is made by detecting HSV nucleic acid via PCR of CSF, which is highly sensitive (98%) and specific (94%) and has replaced brain biopsy as the “gold standard” for diagnosis. HSV is successfully isolated by culture of CSF in less than 2% of cases. Serology is of limited value, because at least ½ of pts with HSV encephalitis have recurrent infections and preexisting Ab responses.
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(MIDII #333)
HSV ENCEPHALITIS => Treatment |
Treatment with IV acyclovir should be started ASAP and cont'd for 14-21 days if diagnosis of HSV encephalitis is confirmed, and in the absence of a confirmed dx of HSV encephalitis if no other dx is confirmed or likely. Early treatment w/acyclovir reduces mortality from 70% to 19%, but even with treatment 62% of pts have moderate to severe residual neurologic sequelae. Empirical acyclovir therapy does not decrease the ability to diagnose HSV encephalitis via PCR for the first 24-48 hrs. Pts older than 30 yrs and those w/duration of symptoms longer than 4 days before initiation of treatment have worse prognoses.
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(MIDII #334)
ARBOVIRAL ENCEPHALITIS => What are arboviruses? |
Arbovirus (arthropod-borne virus) refers to viruses transmitted to humans by biting insects (mosquitoes and ticks). More than 500 arboviruses. Maintained in nature via a transmission cycle between primary nonhuman animal hosts (birds) and arthropod vectors, can be transmitted incidentally to hosts by arthropod vectors. Virus usually causes a prolonged and asymptomatic viremia in its primary host, but a brief and low-level viremia in its incidental (human or animal) host. Most human infections w/arboviruses are asymptomatic. When disease is produced, clinical illness is self-limited but can be severe or fatal.
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(MIDII #335)
What are the 3 main virus families which account for arboviruses causing encephalitis? |
(1)Togaviridae (Alphavirus), ssRNA, (+), enveloped virus. Examples: Eastern equine encephalitis, Western equine encephalitis. (2) Flaviviridae (Flavivirus), ssRNA, (+), enveloped. Examples: Japanese encephalitis, St. Louis encephalitis, West Nile virus. (3) Bunyaviridae (Bunyavirus), ssRNA, (-) segmented, enveloped. Examples: California serogroup, including LaCrosse virus.
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(MIDII #336)
ARBOVIRAL ENCEPHALITIS => Epidemiology |
Most important arbovirus causing encephalitis is Japanese encephalitis virus. Causes 50,000 cases of encephalitis and 10,000 deaths each year in Asia, mainly affecting children. St. Louis encephalitis virus causes 135 annual cases of encephalitis in the US. Viruses causing encephalitis in the US include: Eastern equine encephalitis, Western equine encephalitis, St. Louis encephalitis, and LaCrosse encephalitis. (Also West Nile which will be discussed separately.)
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(MIDII #337)
ARBOVIRAL ENCEPHALITIS => Pathogenesis |
Features specific to arboviruses: mode of transmission is from a bite from an infected vector. There is replication in local tissues, viremia, and hematogenous invasion of the CNS. Neuron is the primary target in the CNS. CNS disease is mainly due to neuronal dysfunction and neuronal death induced directly by the virus. Age of the host is paramount in determining neuroinvasiveness and neurovirulence.
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(MIDII #338)
ARBOVIRAL ENCEPHALITIS => Clinical Features |
Spectrum ranges from clinically inapparent, to fever and headache, to aseptic meningitis, and finally encephalitis. Incubation period is 4-10 days. Transmitted by mosquitoes. Illness is seen during mosquito season (late spring to early fall). When encephalitis occurs, viral agent can't be det'd based on clinical symptoms. Dx depends on epidemiologic factors such as age, geography, lab diagnosis. Clinical manifestations of arboviral encephalitis include acute onset of fever, nausea, vomiting, headache, followed by confusion and disorientation within 24 hrs. Mental status changes range from subtle changes detected only by specific neurocognitive testing to severe disorientation and coma. Cranial nerve abnormalities, weakness, and tremor may occur. Rash, myalgias, photobia. In infants, the only manifestation may be fever and seizures.
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(MIDII #339)
ARBOVIRAL ENCEPHALITIS => Diagnosis, Treatment, Prevention |
(Dx): Isolate virus or detect viral antigen or nucleic acid in the CSF, or detecting an immune response to the individual agent via acute and convalescent serology. (Rx): Supportive. No specific antiviral agents are available. Neurologic sequelae can include cognitive impairment, personality changes, seizures, blindness, and deafness. (Prevention): Vaccines are not available for arboviruses for use in humans except for an inactivated Japanese encephalitis vaccine. Prevention involves decreasing contact between humans and potentially infected vectors.
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(MIDII #340)
ARBOVIRAL ENCEPHALITIS => Eastern Equine Encephalitis and Western Equine Encephalitis Viruses |
Alphaviruses. Involve swamp-dwelling birds, mosquitoes, with horses and humans as accidental dead-end hosts. EEE has been isolated along east coast of North America and South America. WEE in California. Outbreaks in summer, early fall which may be preceded by epizootics in horses. Infants, kids, adults over 55 are most often affected, males and females equally. Infected human is 25 times more likely to experience inapparent infection from clinical illness. Spectrum of illnesses ranges from mild to fatal. Mortality rate of those w/encephalitis exceeds 50%. EEE causes a cloudy CSF w/greater than 1000 WBCs. Western EE occurs everywhere in the US, most common in Central Valley of California. Also in Canada and Brazil. Highest attack rates occur in adults > 55, case fatality rate is 5-10%.
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(MIDII #341)
ARBOVIRAL ENCEPHALITIS => St. Louis Encephalitis Virus |
Flavivirus. Transmission cycle involves birds and mosquitoes. Has caused encephalitis in all areas of US in midsummer/early fall, also occurs in the Caribbean, Central & South America. Infection rates are similar in all age groups but chance of developing clinical encephalitis increases w/age. 75% with illness have encephalitis. Dysuria and urinary frequency occur in 20%. Mortality ranges from 2-12%. Case fatality in the elderly: 30%.
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(MIDII #342)
ARBOVIRAL ENCEPHALITIS => LaCrosse Virus |
Most prevalent virus in the California group of bunyaviruses. Transmission cycle involves chipmunks, squirrels and mosquitoes. Occurs in the Midwestern US, also in Texas and the east coast. Causes encephalitis mostly in rural areas, among 5-10 yr olds, and boys are affected more than girls. Case fatality rate is <2%, but 1/3 of affected persons have abnormal neurologic findings at discharge. Can cause temporal lobe abnormalities on MRI and EEG.
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(MIDII #343)
CLINICAL VIGNETTE: A 66 yr old man from Staten Island experiences onset (in June) of fever, chills, headache, nausea & vomiting, muscle aches, fatigue, muscle weakness, dizziness, decreased appetite and chest pain. After more than 2 wks of low grade fevers, he had abrupt onset of double vision and mental status changes, and is admitted to the hospital. Diagnosis? |
West Nile Virus Encephalitis
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(MIDII #344)
West Nile Virus => Epidemiology |
Since 1st occurrence in US in 1999 (kills birds & humans), spread westward among birds & mosquitoes. In 1999 only NY state was involved; by end of 2004 it had been found in all states except Alaska & Hawaii. West Nile infection of humans usually occurs thru bite of an infected Culex mosquito, so ppl at risk include those spending time outside when mosquitoes are actively biting. Risk: June-October. Mosquito becomes infected when feeding on viremic birds (crows, blue jays). Humans, horses, & other mammals are dead end hosts, do not develop high-level viremia to allow subsequent transmission to others via mosquito bite. Some level of sustained viremia does occur b/c the virus can be spread by organ transplantation; breast-feeding; blood transfusion; and transplacental transmission. Most infected humans are clinically asymptomatic. 1 in 5 infected persons experience a brief febrile illness. 1 in 150 persons will experience a severe illness w/ CNS involvement. Risk is greatest for the elderly. People older than 50 have a 10 fold higher risk of developing neurologic symptoms. Increased risk increases to 40 fold in patients > 80 yrs.
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(MIDII #345)
West Nile Virus => Pathology |
Flavivirus. Member of the Japanese encephalitis serocomplex. Enveloped ssRNA virus with 2 impt glycoproteins: M (membrane) and E (viral envelope). The E glycoprotein mediates virus-host cell binding and elicits most virus-neutralizing Abs. Exact mechanism of CNS infection is uncertain; involves endothelial replication and subsequent crossing of BBB, or axonal transport thru olfactory neurons. Increased risk in the elderly may be due to immune dysfunction leading to prolonged or greater viremia, or due to disruption of the BBB.
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(MIDII #346)
West Nile Virus => Clinical Features |
Incubation period: 2-15 days. Most persons w/clinical illness experience a brief (3-5 days) illness involving fever, headache, myalgias, quick & full recovery. Generalized lymphadenopathy, maculopapular rash involving face & trunk are common. Pts who develop neurologic illness usually develop meningoencephalitis;although isolated meningitis or encephalitis can occur. West Nile meningoencephalitis causes an acute flaccid paralysis syndrome resembling poliomyelitis: asymmetric weakness, decreased deep tendon reflexes, w/no sensory involvement; like polio, involves localized damage to anterior horn cells of the spinal cord. Other features: seizures, cranial nerve abnormalities, ataxia, movement disorders including tremors, myoclonus, & parkinsonism. CSF findings: mild lymphocytic pleocytosis, mild to moderate protein elevation, and normal glucose. MRI may reveal leptomeningeal or periventricular enhancement, or involvement of the thalamus & basal ganglia. West Nile meningoencephalitis has been associated w/up to 10% mortality, long-term morbidity including continuing neurologic abnormalities, fatigue & headaches.
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(MIDII #347)
West Nile Virus => Diagnosis |
IgM-capture Enzyme Linked ImmunoSorbent Assay (ELISA) for CSF and/or serum. (Cross-reactivity w/SLE and other flaviviruses can occur. Positive ELISA results should be confirmed w/plaque reduction neutralization test.) West Nile IgM Ab persists for >6 mo after illness, so presence suggests acute infection only in the context of compatible illness. Viral RNA can be detected via PCR in CSF and serum, but much less sensitive than the IgM Ab. Virus isolation is usually unsuccessful b/c of low level and short duration of viremia. (NYSDOH performs a PCR panel on CSF of pts hospitalized w/viral encephalitis including arboviruses, enteroviruses, herpes simplex virus, cytomegalovirus, varicella zoster virus and Epstein-Barr virus.
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(MIDII #348)
West Nile Virus => Treatment |
No specific therapy is effective for West Nile viral encephalitis, although IFN alpha, ribavirin, and immunoglobulin have been tried and are being evaluated.
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(MIDII #349)
West Nile Virus => Prevention |
Limiting contact between humans and potentially infected mosquitoes. Personal protective measures include avoiding outdoor activity from dusk to dawn (peak mosquito feeding times), use of DEET-containing insect repellent on skin and clothing, wearing long-sleeved shirts and pants while outside, maintaining window screens, and eliminating standing water – breeding ground for mosquitoes.
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(MIDII #350)
Rabies => General Description |
Rabies viruses are rhabdoviridae family of viruses, 2 genera: Vesiculovirus & Lyssavirus. Enveloped, bullet shaped viruses w/non-segmented negative-strand RNA genomes of 11,000 nucleotides that code for 5 proteins (L, P, N, M, and G).
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(MIDII #351)
Rabies => Epidemiology |
60,000 human fatalities due to rabies each year worldwide. UK, Hawaii are rabies free, as well as Spain, Sweden, and Norway. Major foci of rabies in the world are India subcontinent, Southeast Asia, and most of Africa. Rabies is transmitted primary by the bite of an infected animal through inhalation; also transplants. In developed countries, 90% of human exposures are due to wild animals (skunks, raccoons, foxes, bats), and 10% due to domestic animals (dogs, cats, cattle). In developing countries, dogs are the most common cause. Rabies can infect any mammal. Rabies in US has decreased a lot since intro of rabies immunization for domestic animals. Anyone bitten by a wild animal should be considered at risk for rabies infection. Bats are a major source of rabies in US. CDC recommends postexposure rabies prophylaxis for anyone w/bat contact, even if there is no bite, and anyone who awakens from sleep and finds a bat in the room.
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(MIDII #353)
Rabies => Pathogenesis |
Infection in host requires interaction of surface glycoprotein G w/cellular receptor. Replication req's active, ongoing translation and wrapping of template RNA by the N protein as it is synthesized. Actual transcription occurs in the cytoplasm. (+) strand RNA produced serves as template for daughter (-) strand genomic RNA. RNA pol (L protein) has a high misincorporation rate, doesn't have proofreading function, allowing virus to mutate quickly. Virus particles are assembled, bud from plasma membrane as M protein interacts w/cytoplasmic tail of surface protein G. Inside host, virus doesn't need to be enveloped. Doesn't need surface glycoproteins (M & G) to spread within the nervous system. Strains vary in G protein expression. Inverse correlation between G levels and in vivo pathogenicity.
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(MIDII #354)
RABIES => Pathogenesis II How does the rabies virus invade the CNS? |
Centrifugal spread of the virus via the peripheral nerves to the CNS. Rabies is transmitted from saliva from infected animal bites, but may also be transmitted by scratches, secretions, that contaminate mucous membranes, aerosolized virus that enters the respiratory tract, and corneal and solid organ transplants. After entering through a break in the skin, across a mucosal surface, or through the respiratory tract, virus replicates in muscle cells, infects muscle spindle. Infects nerve that innervates the spindle. Moves centrally within axons of those neurons. Replication occurs in peripheral neurons but not glia. Once it reaches the spinal cord the virus spreads throughout the CNS causing neuronal degeneration. Then spreads to the rest of the body via peripheral nerves. High Cx of virus in saliva results from viral shedding from sensory nerve endings in the oral mucosa as well as from replication within salivary glands. Negri bodies in the brain => cytoplasmic inclusions containing considerable amts of viral antigen.
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(MIDII #355)
RABIES => Clinical Features |
Incubation period of 1 wk to 1 yr. Average period is 1-2 months. Length of time from inoculation to clinical disease is det'd by distance from inoculation site to the brain (longer distance, longer incubation, facial bites are particularly dangerous.) Disease exhibits 100% fatality rate once clinical symptoms manifest in an unvaccinated individual. Even in individuals with preexposure or postexposure prophylaxis before onset of clinical symptoms, only 6 documented cases of survival after onset of clinical rabies. Classic presentation: 1 day to 2 wk febrile prodrome, w/parasthesias, pain or numbness at site of bite, followed by anxiety, agitation, delirium, hypersalivation/drooling, and spasm of the pharyngeal muscles at the sound, sight, or taste of water (hydrophobia). 7 to 10 days after onset of neurologic symptoms, generalized flaccid paralysis, seizures, and coma ensue, w/ultimate respiratory and vascular collapse. Alternately and less commonly, rabies may present as pure ascending paralysis without sensory involvement.
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(MIDII #356)
RABIES => Diagnosis |
Dx can be made before death by isolation of the virus or detection of nuclei acid from pt saliva, demonstration of viral antigen in the highly innervated hair follicles obtained by biopsies along the hairline of the neck, detection of viral Ag in touch impressions from the cornea, or the presence of anti-rabies Abs in the serum or CSF of unvaccinated pts. Postmortem diagnosis is made by finding characteristic inclusion bodies in the brain (Negri bodies), RT-PCR of the brain, and/or immunohistochemistry.
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(MIDII #357)
RABIES => Treatment and Prevention |
Once clinical symptoms arise in an unvaccinated individual there is no effective treatment. Rabies may be prevented by both pre & post-exposure prophylaxis. Pre-exposure prophylaxis: 3 doses of rabies vaccine. Recommended for veterinarians & travelers to highly-endemic areas. Booster doses are recommended every 2 yrs & after any exposure. Post-exposure prophylaxis: cleaning the bite site thoroughly; providing rabies immune globulin (passive vaccination); and rabies vaccine (active vaccination) ASAP. Goal of post-exposure prophylaxis is to ensure presence of a rabies-specific immune response in the individual before rabies virus can replicate in the CNS. B/c of long potential latency period, post-exposure prophylaxis should be considered for high risk exposures even if months have passed since the event. In the US, every bite from a wild animal must be considered potentially rabid, as should bites from any dog (domestic or wild) in developing countries. Bites from reliably immunized domestic animals that are available for observation may be managed expectantly. If animal is well after 10 days, no treatment is needed. If animal sickens or dies, post-exposure prophylaxis should be started and cont'd until animal's brain tests neg for rabies.
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(MIDII #358)
RABIES => Additional Info about Rabies Immune Globulin and Rabies Vaccine |
Rabies immune globulin is administered in a single dose, should be injected directly into/around the wound. Original rabies vaccine was developed by Pasteur who dried the spinal cord of a rabid rabbit in the sun (UV inactivation). Vaccine was efficacious, replaced because injection of CNS material precipitated experimental allergic encephalitis which resembled multiple sclerosis. 3 vaccines for human use: all are inactivated virus vaccines. Preferred vaccine is human diploid cell vaccine (HDCV). The vaccination series consists of 5 doses administered in deltoid on days 0, 3, 7, 14, 28.
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(MIDII #359)
How do you go about diagnosing viral infections? |
(1)Have proper index of clinical suspicion. 2 initial questions to ask: Is the syndrome diagnostic of a specific entity (e.g. Herpes zoster, or “shingles”)? Is viral disease in the DDx of the presenting syndrome?
(2)Having knowledge of appropriate specimens to secure the diagnosis. Necessitates having a proper differential diagnosis on hand and a knowledge of viral pathogenesis. Kinds of specimens to consider obtaining are: blood, body fluids (oral or genital secretions, sputum), lesion scraping (from a vesicle), and tissue biopsies. |
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(MIDII #360)
What are the lab methods to diagnose viral infections? |
What are the lab methods to diagnose viral infections?
(1) Isolate virus in tissue culture, animals, embryonated eggs. Tissue cultures is used for HSV which can grow within 24 hrs. Expensive, labor intensive, and slow for many other viruses so labs are moving away from this approach. (2) Ag detection in body fluids, blood, lesion scrapings, tissue. Ag detection routinely used for analyzing skin lesion scrapings for HSV or VZV; also for detection of respiratory viruses in pharyngeal or pulmonary specimens. (3) Nucleic acid detection in body fluids, blood, or tissues. PCR detection of CMV DNA in serum, B19 parvovirus DNA in serum, HSV DNA in CSF. (4) Ab detection: accomplished by detecting IgM (acute phase) Ab or a 4-fold rise in IgG titer. Latter requires interval of 14-21 days between acute & convalescent specimens so is not useful for diagnosis during acute presentation of illness. (5) Tissue biopsy for light microscopy, supplemented by Ag and/or nucleic acid detection. (6) EM of body fluids or tissues (needle in a haystack approach); can apply Ab to specimen and immune aggregate the viral particles if you have a particular pathogen in mind. |
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(MIDII #361)
ANTI-HERPESVIRUS AGENTS (HSV, VZV, CMV) => ACYCLOVIR (ACV) (Also include Valacyclovir, Famciclovir, Ganciclovir, Valganciclovir, Foscarnet, Cidofovir, Formivirsen, Trifluridine, Idoxuridine.) |
Acyclovir is an acyclic guanosine analog. Active vs. HSV, VZV (very modestly, CMV). MOA: Preferentially taken up by virally infected cells, monophosphorylated by virally (HSV, VZV) encoded thymidine kinases (TK). Di & triphosphorylated (TP) by cellular kinases. ACV-TP is the active moiety; acts as a competitive inhibitor of viral DNA polymerase. Viral selectivity is conferred since cellular DNA polymerases are << susceptible to inhibition by ACV-TP than viral DNA polymerases. ACV causes viral DNA chain termination & cessation of viral replication. (PHARM): Administered PO, IV, topically. Oral bioavailability: 15-30%; T ½ = 3 hrs. Primarily renally excreted. (TOXICITIES): Headache, nausea, renal dysfunction, neurological symptoms/signs. (RESISTANCE) Mediated by mutations in viral thymidine kinase (TK) and/or viral DNA pol genes. TK-deficient & TK altered virus can result from mutations in TK gene. Clinically significant infections can be caused by drug resistant HSV & VZV; these are typically seen in immunocompromised hosts.
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(MIDII #362)
ANTI-RESPIRATORY VIRUS AGENTS => For which respiratory viruses do antiviral treatments currently exist? |
Progress has been best for influenza but treatment also exists for respiratory syncytial virus infections. Anti-respiratory virus agents that are FDA approved: Amantadine, Rimantadine, Zanamivir, Oseltamivir, Ribavirin.
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(MIDII #363)
AMANTADINE & RIMANTADINE |
Tricyclic amines w/ “bird-cage” structure. Only active vs influenza A (not B) viruses at clinically achievable Cx's. Share same MOA: interfere w/viral M2 protein. M2 protein acts as an ion channel facilitating hydrogen ion mediated dissociation of matrix protein from nucleocapsid. (PHARM): Orally bioavailable. Amantadine is renally excreted. Rimantadine is hepatically metabolized and then renally excreted. (TOXICITY) Neurotoxicity (amantadine > rimantadine). Drugs are useful for treatment and prophylaxis of influenza A virus infections if circulating strains are susceptible. Drug resistance is mediated by mutations in the M2 coding region and drug resistant virus can be transmitted from person-to-person.
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(MIDII #364)
ZANAMIVIR and OSELTAMIVIR (Viral Neuraminidase Inhibitors) |
Active against influenza A and B viruses. MOA: inhibit influenza virus neuraminidase. Viral neuraminidase catalyzes cleavage of terminal sialic acid residues attached to glycoproteins & glycolipids; necessary for release of virus from host cell surfaces. (PHARM): Zanamavir is administered by oral inhalation device. Oseltamivir is orally bioavailable, converted from an ester prodrug to its active form. Renally excreted. (TOXICITIES) Exacerbation of reactive airway disease for zanamavir. Nausea & vomiting for oseltamivir. (INDICATIONS) Rx for flu A & B within 24-48 hrs of symptom onset. Prophylaxis of flu A & B virus infections. Neither drug interferes w/Ab response to flu vaccination. (RESISTANCE) None so far.
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(MIDII #365)
RIBAVARIN |
Broadly active antiviral agent, used to treat Hep C virus (in combo w/IFN-α) and RSV. Characteristics are: (1) Synthetic nucleoside analog, w/activity vs. broad range of RNA and DNA viruses, including flavi-, paramyxo-, bunya-, arena-, retro-, herpes-, adeno-, & poxviruses. (MOA): complicated! For the flu, ribavirin-triphosphate interferes w/capping & elongation of mRNA and inhibits viral RNA pol. For other viruses, Ribavirin-MP inhibits inosine-5'-monophosphate dehydrogenase, depleting intracellular nucleotide pools, particularly GTP. (PHARM): Administered by aerosol, oral routes. Hepatically metabolized & renally excreted. (TOXICITY): Anemia. Drug accumulates in RBCs and shortens their life span. (INDICATIONS): Oral treatment of hep C virus (in combo w/IFN-α). Aerosol treatment of RSV in children.
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(MIDII #366)
ANTI-HEPATITIS AGENTS: Hep B |
3 approved agents: (1) LAMIVUDINE: nucleoside analog developed for HIV. Lower dose is used for HVB (100 mg/day) than HIV. (2) ADEFOVIR DIPIVOXIL is a nucleotide analog developed for HIV but nephrotoxic at higher doses. Extremely potent vs HBV and approved for HBV infection at lower (safer) dose (10 mg/day). Adefovir is active against lamivudine-resistant strains of HBV. (3) ENTECAVIR: Nucleoside analog, active vs HBV but not HIV. Dosage 0.5 mg/day. Superior to lamivudine in treatment naïve persons. Reduced in pts refractory to lamivudine therapy. (4) Anti-HIV drugs FTC & TDF have anti-HBV activity. Should be taken into account when constructing an anti-HIV regimen in someone w/HBV & HIV infection. (5) HBV is increasingly treated with a 2 drug combo to prevent emergence of resistance.
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(MIDII #367)
ANTI-HEPATITIS AGENTS: Hep C |
Two drugs are used in combo: IFN-α and Ribavirin
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(MIDII #368)
INTERFERONS BACKGROUND: Part of the cytokine repertoire. Possess antiviral, immunomodulatory, and antiproliferative effects. IFN alpha/beta (leukocyte/fibroblast) are coded on chromosome 9. 24 subtypes of IFN-alpha, only 1 of IFN-beta. IFN-gamma is encoded on chromosome 12 and there is 1 subtype. (MOA): Complex! Do not possess inherent antiviral activity but induce an antiviral state within cells. Bind to receptors on cell surfaces, activating receptor-associated tyrosine kinases. (Tyk2 and JAK1 for alpha & beta; JAK1 and JAK2 for gamma). Cytoplasmic proteins (STAT) are phophorylated. Move to nucleus, bind to cis-acting elements in the promotor regions of IFN-inducible genes. What are 5 mechanisms of viral inhibition?? |
(1)1st mechanism of viral inhibition involves synthesis of 2'-5'-oligoadenylate synthetase which is activated by dsRNA and converts ATP into a series of 2'-5' oligo(A)s. These activate RNAase L which cleaves single-stranded mRNAs. (2) 2nd mechanism: Synthesis of dsRNA-dependent protein kinase (PKR, eIF-2 kinase). PKR is activated by dsRNA and autophosphorylated. Phosphorylates alpha subunit of eukaryotic initiation factor-2 which inhibits protein synthesis. (3) Induction of a phosphodiesterase w/inhibition of peptide chain elongation. (4) Synthesis of MxA protein which can bind cytoskeletal proteins and inhibit viral transcriptases. (5) Induction of nitric oxide (NO) by IFN-gamma in MΦs.
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(MIDII #369)
INTERFERONS => Pharmacology, Major Toxicities, Indications for Use |
(PHARM): Must be given parenterally; injected IM or subcutaneously. Inactivated in body fluids/tissues and renally excreted. (MAJOR TOXICITIES): Flu-like symptoms. Hematologic effects, leukopenia, thrombocytopenia. Neuropsychiatric effects: do NOT use IFNs in persons w/ hx of suicidal ideation. (INDICATIONS): IFN-alpha, subcutaneously, is given for Hep C virus, in combo w/ribavirin. IFN-alpha coformulated w/polyethylene glycol (“pegylated” IFN) is more effective for treatment of HCV due to more favorable pharmacokinetic profile. Allows IFN to be dosed once weekly. Can also be given intralesionally for condyloma acuminata. (RESISTANCES): Drug resistances can develop. Mutations in the NS5A gene of HCV result in resistance.
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(MIDII #370)
PASSIVE IMMUNIZATION FOR VIRAL INFECTIONS: Discuss! |
(1)Human immune globulin: prevention of hep A. Prophylaxis & treatment of enterovirus infections in neonates & children w/Ab deficiency. Treatment of B19 parvovirus infection in immunodeficient individuals. (2)CMV immune globulin: (a) Prophylaxis of CMV in solid organ transplant pts. (b) Treatment of CMV pneumonia in combo w/ganciclovir. (3) Heb B Ig: prophylaxis of hep B infection. (4) Rabies Ig: post-exposure prophylaxis for rabies (in combo w/rabies vaccine). (5) RSV Ig: prevention of complications of RSV infection in young children. (6) Palivizumab: humanized RSV monoclonal Ab. Prevention of complications of RSV infection in young children. (7) VZV Ig: prevention of varicella infection in immunocompromised children and adults within 96 hrs of exposure. (8) Vaccinia Ig: available from CDC for complications of smallpox vaccination.
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(MIDII #371)
PRIONS => What are they??? |
Prions are proteinaceous infectious particles responsible for transmissible spongiform encephalopathies (TSEs) in humans & animals. Very small, filterable particles which contain no genome, are resistant to heat & formaldehyde and are not inactivated by UV light.
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(MIDII #372)
Describe SCRAPIE and KURU |
(1)SCRAPIE => 1st description of prions in 1936 w/ scrapie, a slowly progressive neurodegenerative disease of sheep. Infected animals tended to scrape their wool off against walls. Disease could be transmitted by injecting spinal cord material from infected sheep into uninfected animals. (2) KURU => Kuru is a slowly progressing ultimately fatal neurologic disease found in inhabitants of the highlands of New Guinea. Disease occurred in people who ceremonially ate the brains of deceased relatives. Kuru is spread by exposure to brain & mucous membranes of infected individuals. Disease begins insidiously w/prodromal phase of headaches & arthralgias. Followed by inexorably progressive neurologic disease resulting in death within 3 mo - 2 yrs of onset. Cardinal clinical features: cerebellar ataxia, action tremor, & involuntary movement followed in later disease stages by progressively worsening dementia. Histological examination of kuru brains shows neuronal loss & astrogliosis w/the accumulation of PrP^Sc.
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(MIDII #373)
Describe Properties of Prions: (1)What tissues do they infect? (2)How long are their incubation periods? (3)What does infection look like on histopathologic section? (4)Do they cause an inflammatory reaction? |
(1) Major pathologic manifestations of prion diseases are confined to CNS, (2) typically have long incubation periods lasting up to decades, and they are inexorably progressive and ultimately fatal. (3) Histopathologic exam of infected tissue reveals spongiform neural tissue w/vacuolated appearance. Amyloid fibrils aggregated into tangles and astrogliosis is observed. (4) Minimal or no inflammation.
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(MIDII #374)
Molecular biology of Prions |
Prion protein (PrP) is the major component of prions. PrP^c (cellular) is the protein product that is the target for prion disease. Normal host glycoprotein encoded by a single exon of a single copy gene (PRNP on chromosome 20). Assumes an alpha helical structure. Located on cell surface w/glycoinositol phospholipid anchor. Treatment w/proteases results in complete digestion. In infected individuals, the PrP^c protein is deranged to become the PrP^Sc (scrapie) protein, which assembles into beta sheets and is located in cytoplasmic vesicles. Insoluble. Accumulates inside cells instead of being located on the cell surface. Only incompletely digested by proteases. Insolubility contributes to storage problems and aggregation.
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(MIDII #375)
Describe Creutzfeldt-Jakob Disease (CJD) |
Presents as lack of coordination, dementia, motor weakness. Incidence: 1/million. DDx includes Alzheimer's disease. Hereditary form of CJD is much rarer. Typically inherited in autosomal dominant fashion w/variable penetrance. Iatrogenic CJD due to exposure of pts to prions in growth hormone extracted from pituitaries, corneas, & contaminated surgical instruments occurs very rarely, but reminds us that prion diseases are “infectious.” New variant CJD is due to ingestion of BSE (bovine spongiform encephalopathy)-infected meat or bone marrow and has characteristic behavioral & cognitive disturbances. BSE has an incubation period of 20 mo to 15 yrs; characterized by 3 phases: (1) 1st is during first 6 months of infection, of little risk to humans. Rationale for harvesting cattle early in life (<2 yrs). (2) During 2nd phase, prion is concentrated in the CNS and animal is asymptomatic and infectious. (3) Final phase is symptomatic and infectious.
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(MIDII #376)
FATAL FAMILIAL INSOMNIA |
Newly recognized familial human prion disease. Onset of disease is in middle or late life. Avg disease duration of 13 months. Characterized by autonomic dysfunction & sleep disturbances. Neuropathologic changes including neuronal loss and gliosis are found consistently in the anterior ventral and mediodorsal nuclei of the thalamus and occasionally in the olivary nucleus and cerebellar and cerebral cortex.
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(MIDII #377)
GERSTMANN-STRAUSSLER-SCHEINKER DISEASE |
Exceedingly rare human prion disease. Majority of cases are familial with an autosomal dominant pattern of inheritance and virtually complete penetrance. Clinical features are those of midlife progressive spinocerebellar degeneration with associated dementia. Average duration of disease is 5 years with onset in the mid-40's and 50's. Neuropathologic changes are typical of other prion diseases except for a large accumulation of kuru-like amyloid plaques in the cerebellum.
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(MIDII #378)
How are prion diseases diagnosed? |
On the basis of clinical syndrome and history. Brain biopsy/autospy is used, as is tonsillar biopsy. The gold standard of diagnosis is the western blot analysis of protease treated material. At present, there are no reasonable treatments and prevention is key.
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(MIDII #379)
What is VACCINATION? |
Act of artificially inducing immunity from disease. Dates back to 1796 when Jenner showed that inoculating vesicular fluid from cowpox lesions into the skin of susceptible individuals could protect them against smallpox infection. A modified cowpox virus known as vaccinia virus is currently used to protect against small pox and it is from this that we get the term: vaccination.
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(MIDII #380)
Discuss PASSIVE IMMUNIZATION => Providing temporary protection from disease thru admin of exogenously produced Ab. Infants are passively immunized from moms thru transplacental transfer of maternal Abs which protect infant for 3-6 months after birth and allow the infant's own immune system to develop. Pooled human IgG, known as immunoglobulin, is used for passive immunization against hep A and measles after a non-immune person has been exposed to infection but before they develop disease to avoid serious illness. Pooled IgG is also used to prevent infection in individuals w/immune deficiences (X-linked Agammaglobulinemia). Give specific examples of IgG with high levels of Abs specific to certain infectious agents to passively protect individuals from infections!! |
(A) Hep B IgG is used to protect neonates born to hep B carrying women and to protect non-immune persons after exposure to Hep B. (B) VZIG is used to prevent serious chickenpox infections in exposed, non-immune individuals at high risk for severe infection. (C) Rabies IgG is used to protect people exposed to rabies infection during time it takes for immunity to be built up by active immunization. (D) RSVIG is used to protect premature infants and infants with lung disease from serious RSV infection. (E) Tetanus IgG (TIG) is used to prevent tetanus infections in unimmunized, exposed individuals. **Abs provided by passive immunization are short-lived and do not give long-lasting protection of active immunization strategies.
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(MIDII #381)
Discuss ACTIVE IMMUNIZATION |
Inducing body to develop defenses against disease. Accomplished by giving agents that stimulate the body's immune system to produce Abs and/or cell-mediated immune responses against a particular infectious agent.
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(MIDII #382)
How does active immunization cause the production of antigen-specific Abs? |
Most Abs produced by vaccines are thymus-dependent, req activation of T helper cells to initiate B cell proliferation & Ab production. After a vaccine component enters the body it is presented by professional APCs which trigger cascade of cytokines and stimulate maturation of naïve T helper cells into Th2 cells, which produce cytokines that lead to maturation of naïve B cells and release of specific Abs. After initial immune response is induced by vaccine, activated B cells become resting memory cells ready to respond rapidly when antigen is encountered again. Most Abs produced by vaccines are thymus-dependent, req activation of T helper cells to initiate B cell proliferation & Ab production. After a vaccine component enters the body it is presented by professional APCs which trigger cascade of cytokines and stimulate maturation of naïve T helper cells into Th2 cells, which produce cytokines that lead to maturation of naïve B cells and release of specific Abs. After initial immune response is induced by vaccine, activated B cells become resting memory cells ready to respond rapidly when antigen is encountered again.
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(MIDII #383)
Protective Abs against bacterial infections work in several ways depending on the type of Ag encountered. What can they do?? |
(1)Inactivate soluble toxic products (anti-toxins, such as diphtheria vaccine). (2) Facilitate phagocytosis of bacteria (pneumococcal vaccine). (3) Interact with serum complement to damage bacterial membranes and facilitate bacteriolysis (typhoid vaccine). (4) Interfere with bacterium's ability to adhere to mucosal surfaces. ** Protective Abs against viral infections only work when the virus is in extracellular spaces. These Abs may bind to viruses preventing their entry into cells or may interfere w/the uncoating of virus particles or other steps in the viral life cycle.
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(MIDII #384)
Discuss vaccine-induced cell mediated immunity against infection. |
Cell-mediated immunity is directed against intracellular antigens. CTLs recognize peptide Ag complexed w/MHC Class I. Induction of cell-mediated immunity is dependent on Th1 cells which release cytokines causing maturation of naïve cytotoxic T cells which can then recognize intracellular antigens using their TCRs. When TCR of a mature CTL recognizes its antigen complexed with MHC I on the surface of an infected cell it releases substances to kill the infected cell. CTLs also become resting memory cells, ready to become activated as soon as the host is exposed to the antigen again.
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(MIDII #385)
What happens upon first exposure to a vaccine antigen? |
Primary response requires a latent period of several days before humoral (Ab) and cell-mediated immunity can be detected. Circulating Abs do not appear for 7-10 days. Initially IgM. 2 wks (or more) after vaccination the titers of IgG Abs rise. After 2nd exposure to same Ag, heightened Ab and cell-mediated immune responses are seen and occur within 4-5 days after exposure. Response to a vaccine is usually measured by the Ab titer in the serum of the vaccinated host; however, cell-mediated immune responses have been shown to be induced by vaccines and lack of detectable Ab does not mean that the individual is necessarily unprotected by the vaccine.
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(MIDII #226)
Rhinoviruses => Clinical Manifestations |
Common cold, acute sinusitis, otitis media, exacerbations of chronic bronchitis, acute asthma attacks. Rhinorrhea, congestion & sneezing occur in 50-70% of individuals in the 1st 3 days of infection. Sore throat is present in 50% of cases in the 1st 2 days. Pharyngitis can be severe. Exudative rhinovirus pharyngitis has been described. Sore or 'scratchy' throat is associated w/imminent onset of a cold. Correlates w/detection of virus in nasal secretions 10 hrs after inoculation. Hoarseness & cough are less common manifestations of the common cold but may be more persistent, lasting up to several wks, especially if sinusitis or bronchitis arises. High fevers, myalgias and chills are NOT usually seen in rhinovirus infection and should prompt a search for another cause. Symptoms peak on the 2nd, 3rd, and 4th days of infection. Median duration of illness is one wk. 20% of infected individuals have symptoms for longer, and virus can be shed for up to 3 wks.
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(MIDII #227)
Rhinoviruses => Complications |
Most rhinovirus infections are mild and self-limited, but complications can occur. 87% of individs w/ natural rhinovirus infection develop disease in paranasal sinuses. Usually asymptomatic, resolves spontaneously within 2-3 wks. In small number of pts, bacterial superinfection necessitates antibiotic therapy. Exacerbation of chronic bronchitis is a common sequela of rhinovirus infection. Due to inflamm responses to virus. Antibiotics aren't indicated unless there is clear evidence of bacterial superinfection. Yellow or green sputum or nasal discharge is NOT a good predictor of bacterial superinfection of lower airways or sinuses. PMNs are present in sputum & nasal discharge in uncomplicated rhinovirus infections; they cause yellow-green discoloration thru natural myeloperoxidase activity. Viral URIs (upper resp tract infections) precipitate asthma attacks in kids & are linked to 40% of asthma attacks in adults. Rhinovirus-induced changes in airway reactivity may persist for up to 4 wks following URIs, explaining persistent cough seen in individuals following URIs. Cough is NOT bacterial bronchitis and will resolve spontaneously.
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(MIDII #228)
Rhinovirus => Treatment |
No cure other than passage of time during which virus is cleared by host immune system. Host response is responsible for most symptoms of the common cold. Most modern cold remedies try to attenuate host immune response. Decongestants (alone & in combo w/antihistamines or anticholinergics decrease rhinorrhea, nasal discharge, & congestion. NSAIDs and acetaminophen may provide significant symptomatic relief, esp in combo w/decongestants or antihistamines. Anti viral replication drugs have been disappointing. Must be used within short time period (before symptoms have appeared) to reduce symptoms. Do decrease spread of infection in households. Double blind trials have failed to show any benefit of ZINC LOZENGES. Studies do not support effectiveness of ECHINACEA (purple coneflower). Vitamin C's effectiveness has achieved mixed results. There is NO role for antibiotics in treating uncomplicated viral URIs. No evidence to suggest antibiotics prevent secondary bacterial complications of viral URIs. But antibiotics are prescribed for uncomplicated URIs at alarming rates, contribute to antibiotic resistance. Unless there is fever, good evidence of bacterial superinfection, DO NOT prescribe antibiotics for URIs.
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(MIDII #229)
Rhinovirus => Prevention |
Rhinoviruses are transmitted through aerosol and hand contact. Control of nasal secretions and use of virucidal tissues decreases rhinovirus transmission. Proper handwashing, use of virucidal agents, and avoidance of hand-to-mucous membrane exposure (almost impossible) decrease transmission rates. No current rhinovirus vaccines. >100 serotypes of rhinovirus can cause disease in humans. Unlikely that a vaccine will be developed. Prevention relies on avoiding the virus.
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(MIDII #230)
HIV and AIDS => Transmission |
(A) What 3 modes of spread account for nearly all cases of HIV transmission? (B) Cofactors? (C) What is the key determinant of transmission risk in needle stick injuries, mother-to-child transmission, and sexual transmission in sero-discordant couples?
(A) MODES OF SPREAD: (1) Sexual contact (between men or heterosexual); (2) contact w/infected blood or blood-containing bodily fluids; (3) vertical transmission from mother-to-child. (B) COFACTORS: genital ulcer disease; virulence differences in HIV strains; innate resistance to infection by host cells. (C) Level of viral load in the blood is the key determinant for transmission risk in those scenarios named. |
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(MIDII #231)
HIV and AIDS => Epidemiology (A) Is infection with HIV-1 or HIV-2 or both responsible for the worldwide pandemic of AIDS? (B) What is the dominant clade of virus found in the US and Western Europe? (C) Is this clade seen in Sub-Saharan Africa and Southeast Asia? (D) What clades predominate in those locales? |
(A) Worldwide pandemic of AIDS is due to infection w/HIV-1. HIV-2 causes an AIDS-like illness that is less easily transmitted and is largely restricted to populations in West Africa and Brazil. (B) Subtype B is predominantly found in US and Western Europe. (C ) Subtype B is NOT seen in West Africa or Southeast Asia. (D) Clades A and C or E predominate in Sub-Saharan Africa or Southeast Asia.
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(MIDII #232)
HIV and AIDS => Global Epidemiology of HIV Infection |
65 million ppl infected w/HIV in the world. 45 million alive. 20 million dead. Sub-Saharan Africa has the largest number of cases and highest seroprevalence rates. Rapidly growing epidemics in the former Soviet Union, China & India. 14 million children have lost one or both parents to AIDS.
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(MIDII #233)
HIV and AIDS => U.S. Epidemiology |
2 epidemics have occurred in the U.S. One concentrated among men who have sex with men (MSM) and the other among injection drug users (IDUs), their heterosexual partners & children. Fastest growth in the past decade is among the IDUs and their families, especially impacting black and Latina women. In the past 2 yrs another trend w/young MSM returning to high risk sexual activity and acquiring both HIV and other STDs at an increased rate.
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(MIDII #234)
HIV and AIDS => Diagnosis of HIV Infection |
HIV infection is diagnosed by detecting HIV-specific Abs w/2 stage procedure: (1) Screening test by highly sensitive enzyme immunoassay; (2) confirmatory test w/highly specific Western blot if screening test is positive. Abs usually appear 6-12 wks after infection. By 6 months in virtually everyone. Window period w/false negative antibody tests can persist for several months. During this period high levels of HIV viremia are present so tests that detect the virus directly are positive including HIV culture, p24 antigen, and nucleic acid detection tests such as PCR or the branch chain DNA assay.
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(MIDII #235)
HIV and AIDS => Diagnosis of AIDS |
AIDS was originally epidemiologically classified based on indicator conditions such as Kaposi's sarcoma and Pneumocystis pneumonia, rare diseases in the general population only encountered in individuals such as transplant recipients w/suppressed or deficient cellular immunity. In 1993 the CDC definition was amended to include asymptomatic individuals w/<200 CD4 cells in the recognition of the variable and changing course of HIV disease (esp in delay or prevention of opportunistic infections (Ois) by antimicrobial prophylaxis.
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(MIDII #386)
What determines the effectiveness of a vaccine? |
The ability of a vaccine to produce an effective immune response is determined by the vaccine Ags, the genetic background of the vaccinee (HLA type), the physiologic condition of the vaccinee, the manner in which the vaccine antigen is presented, dose, use of adjuvants, and route of administration.
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(MIDII #387)
DETERMINANTS OF EFFECTIVE VACCINE IMMUNIZATION => HLA TYPE |
HLA types vary widely among individuals. Contribute to recognition of different parts of a complex Ag in different populations. Important for vaccines that primarily attempt to elicit cell-mediated immunity (HIV vaccine). Vaccines must contain antigenic molecules that can be recognized and presented by at least one HLA molecule in every individual vaccinated. Differences in HLA types may explain why certain people never respond to certain vaccines (Hep B vaccine).
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(MIDII #388)
DETERMINANTS OF EFFECTIVE VACCINE IMMUNIZATION => Age, Nutritional Status, and Immune Status |
Age, nutritional status, and immune status influence the effectiveness of the response to a vaccine. Young infants do not respond to vaccines because of the presence of maternal Abs. Elderly often have diminished immune responses to vaccines because of waning cellular immunity. Severely malnourished individuals have blunted immune responses and people with immune deficiencies may be unable to respond to many vaccines.
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(MIDII #389)
DETERMINANTS OF EFFECTIVE VACCINE IMMUNIZATION => Type of Vaccine |
Live attenuated vaccines, in which a weakened strain of live infectious agent is given to the vaccinee (measles, mumps, rubella) actually multiply in the recipient until checked by the immune response. Most of these vaccines can confer life-long immunity after a single dose because they allow for large amts of Ag to be presented to the immune system. Killed or subunit (vaccines containing only part of the infecting organism) vaccines in contrast require more than a single dose and often require booster shots (tetanus, rabies, diphtheria) throughout life.
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(MIDII #390)
DETERMINANTS OF EFFECTIVE VACCINE IMMUNIZATION => Dose and Route of Administration |
Usually a dose-response curve between antigen dose and peak response. This response often plateaus. Route of administration may determine the nature of the immune response to a vaccine. Intranasally administered vaccines are more likely to induce local IgA production than parenterally administered vaccines.
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(MIDII #391)
DETERMINANTS OF EFFECTIVE VACCINE IMMUNIZATION => Adjuvants |
Adjuvants are substances added to vaccines that enhance the immunogenicity of Ags. Particularly useful with inactivated vaccines and toxoids. Mechanism of immune enhancement is not completely defined but may include mobilization of phagocytes and delayed release of antigen.
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(MIDII #392)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Live Attenuated Vaccines |
Consist of live organisms that have been specifically modified to make them less virulent than WT pathogens. Have ability to infect the vaccinated host and multiply but do not cause disease (generally). They are the most effective vaccines available. They contain live organisms so their use may be problematic in certain populations (e.g., pregnant women, people with AIDS) and not every organism can be attenuated enough that it does not cause disease but remains capable of inducing an immune response (HIV to date).
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(MIDII #393)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Measles vaccine |
Live attenuated virus vaccine with efficacy of >95% when administered in a single dose to children over the age of 15 months. Because measles can continue to circulate in the 2-5% of the population who do not respond, 2 doses of vaccine are recommended (2nd dose at school entry). Has resulted in 99.75% decrease in measles cases in the US. Travelers should be adequately vaccinated. Recent outbreak of measles in Queens in US born infants who traveled to India before being vaccinated.
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(MIDII #394)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Mumps Vaccine |
Highly effective live attenuated vaccine recommended for all children over the age of 1 who do not have specific contraindications (immunocompromise). Protection is life-long after a single dose although most people receive two doses as part of the MMR vaccine. The mumps vaccine has led to a 98.3% decline in mumps cases in the US since 1968.
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(MIDII #395)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Rubella Vaccine |
Live attenuated vaccine which makes up the 3rd component of the MMR vaccine. Purpose is to prevent congenital rubella syndrome by ensuring that all women of childbearing age are protected against infection. A single dose confers lifelong protection in 95% of vaccinees. Because the live attenuated rubella vaccine can cross the placenta, this vaccine is contraindicated in all pregnant women and within 3 months of a planned conception. Data on 226 women who received rubella vaccine during pregnancy or within 3 months of conception showed no evidence of a congenital rubella syndrome.
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(MIDII #396)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Oral Polio Vaccine |
Live attenuated vaccine given in 3 doses to children at 2, 4, and 6 months of age. Highly effective and easy to administer. Because live polio virus is secreted from the intestines of vaccinated individuals for a short time after vaccination, and because vaccine polio virus can cause paralytic disease this form is no longer used in this country where polio has been eradicated. Oral polio vaccine is still the vaccine of choice for the WHO's effort to eradicate polio from the world.
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(MIDII #397)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Varicella zoster vaccine |
Approved in 1995 for use in the US. Given at 12-18 months of age and is highly effective in preventing severe varicella infections. Recommended for adults who may be exposed to VZV and who are not immune (healthcare workers, daycare attendants,etc.) Vaccine was originally developed for immunocompromised children. Because it can cause chickenpox like symptoms it is currently contraindicated in individuals with severe immunodeficiency. Can cause a mild chickenpox rash in immunocompetent hosts and goes latent in DRG cells with subsequent reactivation zoster. However, it is felt that the risk of zoster in vaccinated individuals is less than that in naturally infected individuals.
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(MIDII #398)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => WHOLE KILLED VACCINES |
Consist of organisms that have been inactivated so they are no longer capable of infecting a host or of multiplying within the vaccinated host. Do not cause disease but can elicit an immune response. Because they do not replicate in the vaccinee they provide less antigenic stimulus than live attenuated vaccines and often require multiple doses to ensure protection. Vaccines are safe and can be used in immunocompromised individuals. Adverse reactions to whole killed vaccines are often seen in children.
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(MIDII #399)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Hepatitis A Vaccine |
Derived from formalin inactivation of hep A virus and is recommended for travelers to areas of the world where hep A is endemic and for children in communities with high rates of hepatitis A. Vaccine is very effective, at least in the short term. Two doses given 6-12 months apart appear to be protective for at least 10 years. Longer term protection may require further boosting.
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(MIDII #400)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Influenza virus vaccine |
Composed of whole or disrupted (split) influenza viruses. Viruses chosen change from flu season to flu season depending upon which strains are likely to circulate. Revaccination is recommended yearly as strains change and Ab levels decline over a 6-9 month period after vaccination. Efficacy of this vaccine is 60-80% in healthy adults. Less in elderly and immunocompromised individuals. Still effective in this group at preventing serious illness, hospitalization, and death. A life attenuated nasal influenza vaccine (Flumist) recently received FDA approval for healthy individuals aged 5-49.
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(MIDII #401)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Pertussis Vaccines |
2 different preparations. (1) Whole cell vaccine, consists of whole killed Bordetella pertussis. (2) An acellular preparation has become available which consists of combos of purified components of the organism and detoxified pertussis toxin. Whole cell pertussis vaccines are associated w/higher rate of adverse events after vaccination than most other commonly used vaccines. 60% of vaccinees had local reactions or fever after receiving the vaccine. Febrile convulsions (without sequelae) were seen in 1/1750 vaccinees. Acellular pertussis vaccine causes fewer local and systemic rxns than whole virus vaccine and is now the favored form of vaccination. Combined with diphtheria and tetanus vaccines to produce the DTP (now DtaP as the acellular preparation is used) given to infants at 2, 4, 6, and 15-18 months with a booster at school entry age.
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(MIDII #402)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Inactivated Polio Vaccine |
Currently polio vaccine of choice in the US. Prepared by formalin inactivation of poliovirus strains and has been formulated to contain antigens recognized by 99% of the population (enhanced potency IPV). More immunogenic than OPV but must be administered parenterally (subcutaneously). Given on the same schedule as the OPV (2, 4, 6-18 months) and has an excellent safety record. Vaccination against polio has resulted in eradication of WT polio infection from the Western hemisphere and from Europe.
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(MIDII #403)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Subunit Vaccines |
Consist of immunogenic parts of whole organisms and are used when attenuation of the organism is difficult and whole killed vaccines are either not immunogenic enough or too toxic. Many subunit vaccines are conjugated, meaning they are attached to protein carriers which greatly enhance their immunogenicity. Subunit vaccines, like killed vaccines, cannot cause disease. Adverse events are rare.
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(MIDII #404)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Haemophilus b vaccine |
Consists of purified high molecular weight haemophilus b polysaccharide (PRP) covalently linked to a carrier protein. Linkage of polysaccharide to the carrier protein greatly enhances the immunogenicity of the vaccine and allows for its use in young infants. Currently 4 licensed preparations of the vaccine which differ in their carrier protein: (1) PRP-D (PRP linked to diphtheria toxoid) is the least immunogenic and is not recommended for use in infants. (2) PRP-OMC (consists of PRP linked to outer membrane protein complex of N. meningitidis) is the most immunogenic formulation. (3) PRP-T (PRP linked to tetanus toxoid) and (4) HbOC (oligosaccharide linked to mutant diphtheria toxin protein) are as effective as PRP-OMC but require an extra dose of vaccine at 6 months. Hib vaccine is generally given at 2 and 4 months of age, with a boost at 12-15 months if using the PRP-OMC preparation. If using PRP-T or HbOC a 3rd dose at 6 months followed by a boost at 12-15 months is recommended. All preparations of the vaccine are quite safe and have resulted in a dramatic decrease in serious Hib infections in vaccinated populations.
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(MIDII #405)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Hepatitis B Vaccine |
Consists of purified, inactivated hepatitis B surface Ag particles derived from recombinant DNA technology. Vaccine is safe, well-tolerated and highly effective. A small number of vaccinated individuals never sero-convert. Vaccination is recommended for all individausl with potential blood/body fluid exposure and is given to all infants in the US (usually in combo with a Hib vaccine).
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(MIDII #406)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Meningococcal Polysaccharide Vaccine |
Contains purified meningococcal polysaccharides of groups A, C, Y, and W135. A single IM dose induces protective Ab levels in over 90% of vaccinees over the age of 2. Adverse events are rare. Vaccine is recommended for high risk groups, including those with complement deficiency, asplenia, and travelers to countries with endemic disease. It is recommended for college students, especially those living in dormitory accommodation. The vaccine does NOT confer protection against group B meningococcus infection.
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(MIDII #407)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Pneumococcal Polysaccharide Vaccine and Conjugated Pneumococcal Polysaccharide Vaccine |
Unconjugated vaccine consist of 23 different serotypes of pneumococcal capsular polysaccharide covering the strains responsible for 85% of all bacteremic pneumococcal disease in the US. This vaccine is recommended for people over the age of 2 with a high risk for pneumococcal disease. The conjugated vaccine consists of polysaccharide from 7 serotypes of pneumococcus linked to protein carriers. Recommended for all children aged 2-23 months. Generally given at 2, 4, 6 and 12-15 months.
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(MIDII #408)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => TOXOIDS |
Modified bacterial toxins that have been rendered non-toxic but retain the ability to stimulate the formation of Abs (antitoxins). Toxoids are generally safe and well-tolerated but do not produce life-long immunity and require booster doses.
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(MIDII #409)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => Diphtheria Toxoid |
Purified preparation of inactivated diphtheria toxin. Highly effective in inducing Abs that will prevent disease although it has little effect on acquisition or carriage of the actual organism, Cornybacterium diphtheriae, that makes the toxin. Local reactions to the toxoid are frequent especially with booster doses. High dose of toxoid is given in combo w/pertussis vaccine & tetanus toxoid to young children (DTaP) and in a lower dose in combo w/tetanus toxoid (Td) to older children and adults. After the initial 3 doses of toxoid, booster doses need to be given every 10 yrs to ensure continued protection against diphtheria. Use of diphtheria toxoid has resulted in a 99.99% decrease in cases of diphtheria in the US from 1921 to 1992.
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(MIDII #410)
CURRENTLY AVAILABLE VACCINES RECOMMENDED FOR GENERAL USE => TETANUS TOXOID |
Purified preparation of inactivated tetanus toxin precipitated w/alum and is one of the most effective immunizing agents known. A course of 3 doses induces protective Abs in over 95% of recipients. It is given to young children as part of the DTaP vaccine and to older children and adults as the Td vaccine. After the initial series of vaccinations, boosters are recommended very 10 years (given as Td to ensure both tetanus and diphtheria protection is given). The most common side effects are fever and local reactions. As local reactions can be quite severe, boosters are recommended only every 10 yrs unless a particularly tetanus-prone wound has occurred, in which case a booster should be given if it has been more than 5 yrs since the last booster. Tetanus cases have decreased over 97% since intro of tetanus toxoid.
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(MIDII #411)
OTHER VACCINES TO KNOW ABOUT => Anthrax Vaccine |
Cell-free filtrate prepared from microaerophilic cultures of an avirulent strain of Bacillus anthracis. Only indicated for those at high risk for anthrax infection (ppl coming into contact with animal hides from endemic areas, lab personnel working with anthrax, and the military). Efficacy is not known. Induces antibodies in 90% of individuals who receive the primary course of 6 subcutaneous injections. Annual boosting is req'd to sustain Ab levels. Mild local rxns are quite common but systemic rxns are very rare.
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(MIDII #412)
OTHER VACCINES TO KNOW ABOUT => BCG Vaccine |
Contains an attenuated strain of M. Bovis (Calmette-Guerin bacillus). Not recommended for general use in the US b/c it can affect the PPD test and is of controversial efficacy. Most effective in preventing complications from disseminated TB in young children and is recommended primarily for infants and young children at high risk of exposure to TB in the US. Because BCG vaccine contains live organisms, it can disseminate in immunocompromised individuals and should not be used in this population. BCG produces a vigorous local immune response and has been instilled into the bladder to produce an immune response in people with bladder cancer.
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(MIDII #413)
OTHER VACCINES TO KNOW ABOUT => Rabies Vaccine |
Inactivated virus vaccine prepared in human or fetal rhesus lung diploid cell culture. The human diploid cell preparation (HDCV) can be used IM or intradermally. Rhesus lung prep (RVA) can only be used IM. Rabies vaccine is used in people likely to be exposed to rabies (veterinarians, certain travelers) or in people who have been exposed to potentially rabid animals. Preexposure prophylaxis is given as 3 doses either IM or intradermally at 0, 7, 21-28 days with follow-up boosting every 2 yrs or when a potential exposure has occurred. Postexposure prophylaxis is given as 5 IM shots on days 0, 3, 7, 14, and 28 along with rabies immune globulin on day 0. Rabies immune globulin is not needed in persons who have received pre-exposure prophylaxis. Local reactions are common (30-74% of vaccinees) and systemic complaints are also frequently seen with Rabies vaccine but no contraindication exists for its administration to at risk or exposed individuals (alternative is certain death!!)
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(MIDII #414)
OTHER VACCINES TO KNOW ABOUT => Yellow Fever Vaccine |
Live attenuated virus preparation. Highly effective and very well tolerated. Excellent immunity is achieved after a single dose of the vaccine. Recommended for travelers to areas of endemnicity and is required by some countries for entry. Live attenuated virus so its use is contraindicated in immunocompromised individuals; although pregnancy is not an absolute contraindication for use.
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(MIDII #415)
OTHER VACCINES TO KNOW ABOUT => Smallpox Vaccine |
Resulted in eradication of naturally occurring smallpox infection on earth. Smallpox vaccines are derivatives of cowpox (vaccinia) virus and are derivatives of 1 of 3 strains: (1) Elstree (Lister, France) strain, (2) EM63 (Moscow) Strain, and (3) NYC Board of Health Strain. Produced from a seed virus propagated on the skin of calves and then processed to eliminate bacterial contamination. Vaccinations are given over the deltoid region of the upper arm using a bifurcated needle dipped in vaccine. Needle is held perpendicular to the skin and pressed in and out 5 times in unvaccinated individual, 15 times in previously vaccinated individuals. Successful vaccination is defined as a pustular lesion or an area of definite induration or congestion surrounding a central lesion 6-8 days after vaccination. Smallpox vaccine is highly effective but has serious adverse consequences which preclude its general use at this time.
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(MIDII #416)
Describe the Adverse Consequences of Smallpox Vaccination |
(A) Vaccinia necrosum: lethal complication of inadvertent vaccination of an immunocompromised host which consists of the insidious progression of an initially normal appearing vaccination with the development of metastatic lesions throughout the body. (B) Eczema vaccinatum: Consequence of local spread and/or dissemination of vaccinia virus infection in individuals with atopic dermatitis. (C) Generalized Vaccinia: nonspecific term used to describe a vesicular rash that develops after vaccination. Unlike actual generalized infection seen in vaccinia necrosum or eczema vaccinatum, these reactions can be seen in normal hosts, are not accompanied by systmeic symptoms, and do not yield virus on culture of the lesions. (D) Erythematous Urticarial Eruptions: Erythematous rashes observed in otherwise healthy individuals 7-12 days after vaccination. (E) Postinfectious encephalitis is one of the most serious complications of vaccination in normal hosts with a mortality of 10-30%. It occurs in 1 in 100,000 primary vaccinees. (F) Myocarditis: Since reactivation of smallpox vaccination in military personnel and selected civilian populations, myocarditis, pericarditis, and myopericarditis have been reported. Do not vaccinate people with preexisting heart disease.
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(MIDII #417)
Why are biological agents advantageous weapons? |
(1)Potential for wide dissemination with mass casualties at low cost.
(2) Perpetrators can protect themselves as delayed onset allows time to escape. (3) Panic engendered wreaks more havoc than the weapon itself. |
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(MIDII #418)
Describe characteristics of the ideal biological weapon and list potential agents. |
The ideal bioweapon is silent, odorless and tasteless, inexpensive, easy to produce, hardy, transmitted person-to-person, causes lethal or disabling disease, and has no effective treatment or prophylaxis. Potential agents include: (Bacterial) => anthrax, brucellosis, plague, Q fever, tularemia; (Viral) => smallpox, viral hemorrhagic fever; (Toxins) => botulism, ricin, staph enterotoxin B.
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(MIDII #419)
Describe the general characteristics of BACILLUS ANTHRACIS |
Non-motile, Gram positive rod. Produces 3 exotoxins: EDEMA FACTOR (EF), LETHAL FACTOR (LF), and PROTECTIVE ANTIGEN (PA). PA binds to cell surface receptors and (upon proteolytic activation) forms a membrane channel that mediates entry of EF and LF into the cell. EF and PA form a toxin referred to as “edema toxin.” LF and PA form “lethal toxin”, the dominant virulence factor produced by B. anthracis and the major cause of death in infected animals. Clinically, anthrax can manifest in three ways, depending on the route of inoculation: (1) cutaneous, (2) inhalational, and (3) intestinal.
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(MIDII #420)
Describe CUTANEOUS ANTHRAX |
Most common manifestation of anthrax infection. Accounts for 95% of all cases in developed countries. Route: direct inoculation of skin by spores w/incubation period of 1-7 days (up to 14 days). Clinical findings are characteristic. Infection begins as a pruritic macule which enlarges and within 1-2 days develops into a round ulcer surrounded by vesicles. A black ESCHAR develops with associated edema and over 1-2 weeks softens and separates, leaving a permanent scar. In untreated infection there is a ~5-20% fatality rate. Dx can be made clinically by an experienced clinician. Confirmation may include gram stain w/culture or PCR of vesicular fluid at border of skin lesion. Skin biopsy with culture and PCR or immunohistochemistry. Serology looking for IgG antibody to protective antigen.
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(MIDII #421)
Describe INHALATIONAL ANTHRAX |
Very rare with only 18 cases in the US between 1900-1978. None reported from 1978-October 2001. Route of infection is inhalation of spores (1-5 microns) into terminal bronchioles and alveoli where they may live for up to weeks. Spores are taken up by MΦs and brought to regional lymph nodes. In lymph nodes, spores germinate producing actively growing anthrax, which proliferates in MΦs, secretes toxins, and enters the bloodstream. Regional lymph nodes grow & hemorrhage during this infectious stage. Initial symptoms resemble the flu w/malaise, fever, cough, & body aches. Later symptoms: high fever, vomiting, respiratory distress, and necrotizing hemorrhagic mediastinitis. Disease can be fatal within 24-36 hrs.
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(MIDII #422)
INHALATIONAL ANTHRAX => Diagnosis |
Dx is tough b/c findings are nonspecific. Chest XRAY may reveal mediastinal adenopathy & pleural effusions. Gram stain, culture, PCR of blood, pleural fluid, and CSF may produce the diagnosis. Suspected cultures should be sent to NYCDOH and/or CDC, both which can make diagnoses. Antibiotics are effective against vegetative B. anthracis but not against the spore form. Unfortunately, in 'advanced disease' the mortality rate is 100% despite most aggressive therapy. Mortality decreases with early treatment. 6/11 cases in 2001 survived w/early aggressive therapy.
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(MIDII #423)
INTESTINAL ANTHRAX |
Rare, associated with epidemics usually occurring during periods of extreme hardship when meat from animals dying of anthrax is eaten. Incubation period of 3-7 days. 2 clinical presentations: abdominal and oropharyngeal. (A) Abdominal anthrax: symptoms are nonspecific with nausea, vomiting, anorexia, and fever. With progession of disease abdominal pain, hematemesis, and bloody diarrhea develop which progresses into shock, cyanosis, and death. (B) In the oropharyngeal form, edema and tissue necrosis occur in the cervical area. Main clinical features: sore throat, dysphagia, fever, lymphadenopathy, & toxemia. Dx includes culture of vomitus or feces.
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(MIDII #424)
Discuss: Anthrax Vaccine |
Sterile filtrate of cultures for an avirulent strain of anthrax that elaborates protective Ag. 100% effective against cutaneous infection, and “possibly” effective against inhalational disease. Current stocks of vaccine are limited. Prophylaxis comes in 2 types: (1) Pre-exposure Prophylaxis: vaccination of people at high exposure risk (US military since 1997, CDC lab response network, decontamination workers, occupations with high risk of exposure to contaminated animals) and (2) Post-exposure Prophylaxis: vaccination of people exposed to aerosolized anthrax spores to prevent germination and progression to inhalational anthrax. Also, disease can be prevented if antibiotic therapy is cont'd until all spores have been cleared or controlled by the immune system. Spores can live up to 100 days post exposure in mediastinal lymph nodes, so it is recommended that exposed individuals stay on antibiotics (Cipro) for 100 days (if not vaccinated. 30 days with 3 vaccine doses at 0, 2, 4 weeks post exposure).
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(MIDII #425)
SMALLPOX => What makes smallbox a good bioterrorist weapon? |
Aerosol transmission with rapid person-to-person spread. Severe morbidity and mortality especially in non-immune populations (worldwide immunity has waned since the disease was eradicated), clinical inexperience (most practicing physicians have never seen a case), potential to overwhelm medical care and public health systems, and a high secondary attack rate.
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(MIDII #426)
SMALLPOX => How is smallpox spread? What is the clinical presentation? |
Smallpox is spread by aerosol route. Infectious particles enter through oral & respiratory mucosa. Migrate to regional lymph nodes, replicate. Then initial asymptomatic viremia occurs 3-4 days post-exposure. Virus multiplies in the reticuloendothelial tissues leading to secondary viremia by day 8. Symptoms then begin w/abrupt onset of high fever, malaise, rigors, vomiting, backache and headache followed 2-3 days later with a maculopapular rash. Pts are NOT infectious until the rash appears. Rash starts as a maculopapular rash which is deeply embedded in the dermis on the face (including the oral mucosa), and then spreads down and out to the arms, trunk, legs. Lesions found on palms and soles. Rash develops from maculopapular eruption to vesicles, then pustules (just like in chickenpox). However, lesions develop at the same time (synchronous) unlike chickenpox in which different lesions are at different stages of development (cropping).
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(MIDII #427)
SMALLPOX => Diagnosis |
Astute physician to distinguish smallpox from chickenpox. Importance differences between the two: (INCUBATION) Variola is 7-17 days; Varicella is 14-21 days; (PRODROME) Variola is 2-4 days; Varicella is minimal; (DISTRIBUTION) Variola is centrifugal; Varicella is centripetal; (EVOLUTION) Variola is synchronous; Varicella is cropping; (Depth of Lesion) Variola is dermal; Varicella is Subcutaneous. **A swab of vesicular/pustular fluid can be cultured for smallpox at the CDC's BSL4 lab. PCR assay is available thru the CDC. Strict quarantine of suspected cases with respiratory and contact isolation is mandatory. NO proven treatment, although cidofovir is effective in invitro.
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(MIDII #428)
SMALLPOX => Vaccine |
Modern vaccine (dryvax) is administered by a bifurcated needle which is repetitively jabbed (15 times) into the skin of the person to be inoculated. Needle must draw blood to be effective. High levels of protection are present for 3 yrs, but immune response to variola wanes over time. Not clear if people vaccinated in the early 70's will still be protected. Vaccine is not benign. Side effects include: muscle aches, fatigue, headache, nausea, fever, pain and injection site, regional lymphadenopathy. Acute viral illness can occur with vaccine. Real risk.
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(MIDII #429)
SMALLPOX => Contraindications to the Vaccine |
Immunodeficiency: high risk of side effects (progressive vaccinia); Eczema (eczema vaccinatum); pregnancy; allergies to polymyxin B (an antibiotic used in preparation of the vaccine); and acute or chronic skin conditions. Adverse reactions in the general population are rare but do occur. Inadvertent innoculation of an unimmunized contact is most common (1 in 1700 vaccinees). Postvaccinal encephalitis occurs in 1/80,000 primary vaccinees and death in 1 in a million. Vaccinia immunoglobulin (VIG) can be used to ameliorate the adverse effects of the vaccine. Supplies of VIG are limited. Obtained from vaccinated donors and the pool is very small. US has enough vaccine to vaccinate everyone in case of an attack. Recent studies suggest that the vaccine is as effective at a 1:5 dilution as undiluted which will further increase the supply.
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(MIDII #430)
Public health infrastructure is CRITICAL in responding to a suspected bioterror attack! Discuss. |
Detection of a potential outbreak is critical as is follow up to confirm its existence and to identify the etiology (intentional vs. natural). Once outbreak is detected, medical community, law enforcement, and other agencies will be notified and an epidemiologic and criminal investigation will be carried out. Active surveillance program will be put in place to track morbidity and control measures implemented. Cooperation is crucial. Prevention is worth a pound of cure! Strengthen and enforce the UN's biologic and chemical weapons conventions, restrict sale of potential bioweapons organisms, safeguard research stocks, etc.
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(MIDII #431)
What is an EMERGING/RE-EMERGING INFECTION? |
Refers to 3 circumstances: (1) A new, previously known infectious agent or disease. (2) A previously described infectious agent presenting: (a) in a new geographic location; (b) as a new syndrome; (c) in a new type of host; (d) with a new or broader resistance pattern. (3) New or previously described infectious agents used as bioweapons.
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(MIDII #432)
List Examples of Selected Emerging/Re-Emerging Infections in the Past 30 Years! |
HIV/AIDS; Legionairre's disease; Lyme disease; Toxic-shock syndrome; Hantavirus pulmonary syndrome; Ehrlichiosis; Human T-cell lymphotrophic viruses I and II; Human herpesviruses 6 and 8; West Nile virus; Ebola virus; GB virus C; Transfusion-transmitted virus (TTV); Severe acute respiratory syndrome (SARS); Avian influenza virus; Monkeypox; Bovine spongiform encephalopathy (vCJD); Escherichia coli 0157:H7; Helicobacter pylori; TB, esp MDR-TB; Vancomycin resistant enterococci; Vancomycin intermediate/resistant Staph aureus; Intentional use of anthrax as a bioweapon.
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(MIDII #433)
Why do infectious agents emerge or re-emerge? |
Numerous reasons explain occurrence of emerging/re-emerging infections. Ecologic changes (flood, famine), changes in human behavior (population growth, migration, war, sexual practices, injection drug use); international travel and commerce; technological advances (globalization of food supplies, organ/tissue transplantation, immunosuppressive drugs, antibiotic use); microbial adaptation; breakdown or deterioration in public health measures; and advances in basic science (facilitating new microbe detection).
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(MIDII #434)
Identifying Disease Causation: Koch's Postulates |
When faced with a new disease or syndrome and a potential etiologic agent has been ID'd, one generates a hypothesis of causality and then a series of investigations are undertaken to prove the hypothesis. Include in vitro studies, development of animal models, and human studies. Goal is to fulfill Koch's postulates, which are: (1) Organism is always found with the disease. (2) Organism is not found with any other disease. (3) The organism, isolated from one who has the disease, and cultured through several generations, produces the disease in experimental animals. (4) Even when the infectious disease cannot be transmitted to animals, the 'regular' and 'exclusive' presence of the organism (postulates A and B) proves a causal relationship.
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