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18 Cards in this Set
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A 4-year-old child presnts to a physician with purpura. Questioning of the mother revleas that the child has a history of eczema and recureent pneumococcal pneumonia. Blood studies demonstrate thrombocytopenia and a selective decrease in IgM. Patients with this disorder have a 12% change of developing which of the following potentially fatal malignancies?
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Non-Hodgkin's lymphoma
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( Immunology General Principles: 54%); NOTE: I HAVEN'T LEARNED THIS YET IN LECTURE. This patient has Wiskott-Aldrich syndrome, which is an X-linked partial combined immunodeficiency disorder. It presents clinically as the triad of thrombocytopenic purpura, eczema, and recurrent opportunistic infections with organisms having polysaccharide capsules, such as Streptococcus pneumoniae. The patients characteristically have decreased serum IgM and T-cell deficits (which appear later in life). Most patients die before the second decade of life, either from infection or from non-Hodgkin's lymphoma. Bone marrow transplanatation has had some therapeutic success in these patients. None of the other neoplasms listed occurs with greater frequency in patients with Wiskott-Aldrich syndrome. *MY INCORRECT ANSWER: CHRONIC MYELOGENOUS LEUKEMIA
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A 35-year-old woman consults an ophthalmologist because of double vision and droopy eyelids. She also has complaints of generalized muscle weakness. IV injection of edrophonium dramatically, but only briefly, reverses her symptoms. This patient's most probably disease has a pathophysiologic basis that is closest to that of which of the following conditions?
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Insulin resistance
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( Immunology General Principles: 32%): This patient has myasthenia gravis, which was suspected based upon the woman's clinical presentatjion and confirmed with the response to the short-acting anticholinesterase drug, edrophonium. Myasthenia gravis is an autoimmune disease in which antibodies directed against the acetylcholine receptor of the muscle side of the neuromuscular junction block the ability of the receptor to bind acetylcholine. Of the diseases listed above, only insulin resistance is produced by a similar mechanism, i.e., antibodies to insulin receptor block the receptor's ability to bind to insulin. *Bullous pemphigoid choice: Bullous pemphigoid is characterized by antibodies directed against the basement membrane of the skin that damage the basement membrane and cause blister formation. *DIABETES MELLITUS TYPE 1 (SOME CASES) and Idiopathic Addison disease CHOICES: SOME CASES OF TYPE 1 DIABETES MELLITUS AND IDIOPATHIC ADDISON DISEASE ARE CHARACTERIZED BY HUMORAL, AND PROBABLY CELL-MEDIATED, REACTIONS AGAINST THE CELLS IN THE ENDOCRINE TISSUE. *Systemic lupus erythematosus: SLE is characterized by circulating and locally generated immune complexes mediating the pathophysiology.
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A 23-year-old man develops explosive watery diarrhea with blood, fecal leukocytes, and mucus approximately 3 days after eating chicken that was improperly cooked. Curved rods were found in the fecal smear along with red blood cells and leukocytes. Which of the following pathogens is the most likely cause of these symptoms?
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Campylobacter jejuni
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(Microbiology Gastrointestinal: 70%): Campylobacter jejuni is a pathogen causing an invasive enteric infection associated with ingestion of raw or undercooked food products, or through direct contact with infected animals. In the U.S., ingestion of contaminated poultry that has not been sufficiently cooked is the most common means of acquiring the infection. The patients typically have bloody diarrhea, abdominal pain, and fever. The presence of fecal leukocytes indicates an invasive infection. The organism is a gram-negative rod with a curved "comma-shape" or "S-shape." *Enterotoxigenic E. coli choice: Enterotoxigenic E. coli causes the classive traveler's diarrhea. The infection is non-invasive and is acquired via the fecal-oral route through consumption of unbottled water or uncooked vegetables. The major manifestation is a copious outpouring of fluid from the GI tract presenting as explosive diarrhea. This is due to the action of one of two types of enterotoxins on the GI tract mucosa. *SHIGELLA SONNEI CHOICE: SHIGELLA SONNEI PRODUCES A SYNDROME VERY SIMILAR TO C. JEJUNI. HOWEVER, THE ORGANISM APPEARS AS A GRAM-NEGATIVE ROD ON GRAM'S STAIN. IT DOES NOT HAVE A COMMA SHAPE. TRANSMISSION IS FROM PERSON TO PERSON VIA THE FECAL-ORAL ROUTE. INFECTION REQUIRES A LOW INFECTIVE DOSE, SINCE THE ORGANISM IS FAIRLY RESISTANT TO GASTRIC ACIDITY. *Staphylococcus aureus choice: Staphylococcus aureus produces food poisoning due to the ingestion of a pre-formed enterotoxin. THe organism is present in food that is high in salt content, such as potato salad, custard, milk shakes, and mayonnaise. The patient presents with nausea, vomiting, and abdominal pain, followed by diarrhea beginning 1-6 hours after ingestion of the enterotoxin. *Vibrio cholerae choice: produces a secretory diarrhea due to increases in cAMP in the intestinal cells. The organism is not invasive. The patient presents with the sudden onset of painless, watery diarrhea that becomes voluminous, followed by vomimting. The stool appears nonbiliouis, gray, and slightly cloudy with flecks of mucus, no blood, and a sweet odor.
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A 16-year-old girl presents with a painfully enlarged lymph node in her right axilla. Peripheral blood counts are within normal limits. The lymph node is biopsied, and numerous granulomas filled with neutrophils and necrotic debris are observed. Which of the following organisms could produce this disease?
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Bartonella henselae
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(Microbiology Heme./Lymph: 65%): Bartonella henselae is the infective agent of cat scratch disease, which generally presents as regional lymphadenopathy with or without low fevers and headaches. Bartonella is a gram-variable pleomorphic rickettsial organisms that is introduced to the skin in a cat bite or scratch. It produces a self-limited granulomatous response in the draining lymph nodes. *Borrelia burgdorferi answer choice: Borrelia burgdorferi is a spirochetal organism that is transmitted by a tick bite (Ixodes spp.), producting Lyme disease. Lyme disease progresses from a skin rash to fevers, headache, and pain over about one month. It may produce lymphadenopathy, but is not associated with granuloma formation. *CHLAMYDIA PSITTACI CHOICE: CHLAMYDIA PSITTACI INFECTION OCCURS AFTER CONTACT WITH INFECTED BIRD DROPPINGS AND PRODUCES AN ATYPICAL PNEUMONIA. THE CENTRAL NEROUVS SYSTEM MAY ALSO BE INVOLVED, BUT LYMPH NODES ARE SPARED. CHLAMYDIA TRACHOMATIS IS THE CHLAMYDIAL SPECIES THAT TYPICALLY PRODUCES SUPPURATIVE NODAL GRANULOMAS (LYMPHAGRANULOMA VENERERUM). *Coxiella burnetti choice: Coxiella burnetti infection is transmitted by inhaling dusts or drinking milk from infected mammals, especially sheep and cows. The disease in humans, Q fever, is marked by milk nonspecific symptoms or pneumonia, and may progress to myocarditis or hepatitis. *Rickettsia prowazekii choice: Rickettsia prowazekii produces epidemic (louse-borne) typhus, which is transmitted by body lice and produces a rash akin to Rocky Mountain spotted fever. Although the organism may reside in the lymph nodes in dormancy, it does not elicit granuloma formation.
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A 4-year-old child is referred to a specialist for the diagnosis of a potential immunologic defect. Since the age of 14 months, he has been plagued with repeated infections with Candida, Staphylococcus, and Klebsiella. At the present time, the child is suffering from a large, painful boil on one knee. Peripheral blood leukocytes have a negative neutrophil oxidative index. Culture of the pus of the boil grows Staphylococcus aureus. Which intracellular killing mechanism is still operation in phagocytic cells in this abscess?
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defensins
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(Immunology General Principles: 32%): This child has chronic granulomatous disease (CGD), which is a genetic defect in one or more of the subunits of NADPH oxidase. Activation of this membrane-bound oxidase is the critical first step in the generation of toxic oxygen radicals within the phagolysosome. ONe of the products of this reactjion, hydrogen peroxide, serves as the substrate for the second most important killing mechanism: myeloperoxidase acting to produce toxic halide radicals. If a person with CGD is infected with a catalase-positive organism, the substrate of the myeloperoxidase system is degraded, and thus the only remaining functional intracellular killing mechanism involves the other contents of the lysosomes (lysozyme, defensins, lactoferrin, and hydrolytic enzymes). *HYDROGEN PEROXIDE CHOICE: HYDROGEN PEROXIDE IS THE SUBSTRATE NECESSARY FOR THE FUNCTION OF THE MYELOPEROXIDASE ENZYME SYSTEM. IT WOULD BE DESTROYED BY THE CATALSE-POSITIVE ORGANISM IN THE ABSCESS DESCRIBED. *Hypochlorite choice: Hypochlorite is generated in the myeloperoxidase arm of the intracellular killing pathway. It would not be produced in this abscess since the catalase-positive organism would destroy the substrate for myeloperoxidase. *Myeloperoxidase choice: Myeloperoxidase is an enzyme present in the lysosomes that acts on hydrogen peroxide to produce toxic halide radicals. Since the abscess in this case is caused by a catalase-positive organism, the substrate for myeloperoxidase would be destroyed. *NADPH oxidase choice: NADPH oxidase is the membrane-bound oxidase that is genetically absent in a person with CGD.
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A composite virus is created in a laboratory. The capsid of coxsackie virus A is used to deliver the naked genomic material of five viruses to appropate target cells. After 24 hours in culture, the total virus per culture is determined. Use of which of the folloiwng viruses' naked genomic material in this fashion would result in the absence of progeny viruses?
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Reovirus
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(Microbiology General Principles: 31%): Reovirus is a double-stranded RNA virus that is not infectious in the absence of its polymerase enzyme. In its most simple form, this question is asking if you know which viruses must carry a polymerase in their capsid to complete their life cycle. Viruses that cannot complete their life cycles without theirn own polymerase include all of the negative-sence RNA viruses, the double-stranded RNA virus, and the retroviruses. Other viruses require unique polymerases, but are capable of producing them once viral mRNA is made inside the cell. *ADENOVIRUS CHOICE: ADENOVIRUS IS A DOUBLE-STRANDED DNA VIRUS THAT DOES NOT REQUIRE A POLYMERASE TO BE CARRIED IN ITS CAPSID. *Calicivirus choice: Calicivirus is a positive-snse, single-stranded RNA virus whose naked genome would produce progeny in this situation. *Herpesvirus choice: Herpesvirus is a double-stranded DNA virus that does not require a polymerase to be carried in its capsid. *Flavivirus choice: Flavivirus is a positive-sense, single-stranded RNA virus whose naked genome would produce progeny in this situation.
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A family is referred to a genetic counseling clinic because one of the parents is discovered to have a reciprocal translocation involving chromosomes 14 and 22. One of the children of the family received an unbalanced chromosome complements, resulting in a partial monosomy of one chromosome. The chromosome for whichere there is a monosomy is shown to be one encoding immunoglobulin genes. Such an event could result in the loss of which of the following pairs of genes involved in the synthesis of immunoglobulins?
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C gene for gamma chain and C gene for alpha chain
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(Immunology General Principles: 18%): The genes for the synthesis of the entire heavy chain are present on human chromosome 14. Of the options given above, the only genes that are presnt on one chromosome are for the C (constant) regions of the heavy chains. The heavy chains determine the identity of the immunoglobulin isotypes: IgG, IgM, IgA, IgD, and IgE. *C gene for gamma chain and C gene for kappa chain choice: The C gene for the gamma heavy chain is one chromosome 14, and the C gene for the kappa light chain gene is on chromosome 2. *V GENE FOR KAPPA CHAIN AND C GENE FOR THE EPSILON CHAIN: THE V GENE FOR THE KAPPA LIGHT CHAIN GENE IS ON CHROMOSOME 2. THE C GENE FOR THE EPSILON HEAVY CHAIN IS ON CHROMOSOME 14. *V gene for lambda chain and C gene for kappa chain choice: The V gene for the lambda light chain gene is on chromosome 22. The C gene for the kappa light chain gene is on chromosome 2. *V gene for lambda chain and V gene for heavy chain choice: The V gene for the lambda light chain gene is on chromosome 22, and the V gene for the heavy chain gene is on chromosome 14.
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A 6-year-old child is taken to a pediatrician because of a severe sore throat that is accompanied by a rash. Examination of the head and neck reveals pharyngeal injection, swollen, bright red tonsils with discrete white spots on the surface, and enlarged anterior cervical lymph nodes. Examination of the skin reveals a diffuse, erythematous, symmetrical rash that blanches on pressure, has a slightly rough sand-paper like texture, and is most prominent on the neck, chest, and folds of the axilla, elbow, and groin. The strain of the organism that produces the child's disease would be most likely to differ from a less pathogenic strain of the same organism in which of the following ways?
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By containing a phage
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(Microbiology General Principles: 42%): The rash described is that of scarlet fever, which can be a complication of streptococcal sore throat (as in this question) or streptococcal wound infection. In past centuries, scarlet fever was a major childhood disease that often caused death, but it hs become much less common (possibly, as a result of early antibiotic therapy) and is now only a rare cause of death. Strains of streptococci that cause scarlet fever are beta-hemolytic group A streptococci that have been infected by a phage. The precise role of the phage is still unclear but may involve upregulation of toxin-producing genes, since some of the streptococcal strains that do not produce scarlet fever still carry genes for toxin production. *BY CONTAINING LIPOPOLYSXACCHARIDE CHOICE: LIPOPOLYSACCHARIDE IS FOUND IN GRAM-NEGATIVE ORGANISMS. *By forming spores choice: Spore formation is a feature of Bacillus and Clostridium. *By lacking cell walls choice: Mycoplasma are organisms that lack cell walls. *By producing lecithinase choice: Lecithinase is an enzyme produced by Clostridium.
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A patient with chronic active hepatitis B develops a low-grade fever and a generalized petechial rash. Routine urinalysis detects proteinuria. Needle biopsy of the kidney demonstrates the presence of irregular deposits of antigen-antibody complexes with underlying areas of neutrophilic infiltration and tubular damage. Which of the following is most important in the removal of these immune complexes from the blood stream?
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C3b
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(Immunology General Principles: 54%): Lesson learned: IF YOU DON'T KNOW WHAT THE ANSWER CHOICE IS, THEN DON'T CHOOSE IT FOR AN ANSWER! C3b is the most critical molecule in both the classical and alternative complement pathways. C3, the most abundant protein of all the complement proteins, is cleaved into C3a and C3b. C3b attaches to bacterial surfaces for opsonization by phagocytes. C3a binds to mast cells and basophils, activating them and producing histamine release. C3b is also critically involved in the removal of immune complexes from the serum. Immune complex-mediated glomerulonephritis is common in many infectious diseases, where the chronic persistence of antigen and antibody mediate damage in the small vasculature by immune complex-mediated hypersensitivity. *C1q choice: C1q is a complement component in the classical pathway. It binds to the constant heavy domain of an IgG molecule that has reacted with the bacterial surface epitope. C1q is not involved in opsonization or removal of immune complexes, as it simply functions as an enzyme in the early complement cascade. *C5 choice: C5 is a protein that, once split into C5b, initiates the assembly of the membrane attack complex. This complex consists of C5b, C6, C7, C8, and polymerization of C9, and is responsible for lysis of the bacteria. C5a is a strong chemotactic molecule. *C5a choice: C5a is a strong chemotactic factor for neutrophils and results in stimulation of the inflammatory response. *FACTOR B CHOICE: FACTOR B IS AN ACTIVATOR PROTEIN OF THE ALTERNATIVE PATHWAY. IT COMBINES WITH C3B TO FORM C3bBb. C3bBb IS THE C3 CONVERTASE OF THE ALTERNATIVE PATHWAY. SINCE THE ALTERNATIVE PATHWAY IS TURNED ON BY THE SURFACES OF BACTERIA, AND THIS IS A VIRAL INFECTION , FACTOR B IS UNLIKELY TO BE INVOLVED.
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A 27-year-old woman presents to the emergency department complaining of 10-12 episodes of nonbloody diarrhea per day for the past 2 days, along with severe abdominal cramsp, nausea, vomiting, and a low-grade fever. She states that she just returned from a vacation to Mexico. While in Mexico, she did not drink any of the local water and ate only cooked foods and a few fresh salads. If fecal leukocytes are present, the patient should most likely be empericially treated with:
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Ciprofloxacin
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(Microbiology Gastrointestinal: 50%): When inviduals travel from one country to another with marked differences in climate and sanitation standards, the risk for development of traveler's diarrhea is dramatically increased. This type of diarrhea is most likely to develop within 2-10 days after ingesting local water and/or eating fresh fruits and vegetables (such as a fresh salad) that could have been "washed off" with the local water. Traveler's diarrhea is often accompanied by the appearance of approximately 10 or more episodes of diarrhea per days, as well as severe abdominal cramps, nausea, vomiting, and a mild fever. Depending on the causative bateria, blood and/or fecal leukocytes may be present. Most cases of traveler's diarrhea are caused by enterotoxigenic Escherichia coli, Shigella species, and Campylobacter jejuni. The most commonly used agents to treat traveler's diarrhea are the fluroquinolones, such as ciprofloxacin, ofloxacin, and norfloxain. Trimethoprim/sulfamethoxazole is most commonly used in treatment children. None of the other agents are indicated for the treatment of traveler's diarrhea. *Acyclovir choice: Acyclovir is an antiviral agent indicated for the treatment of herpes virus infections. *Mebendazole choice: Mebendazole is a broad-spectrum antihelminthic indicated for the treatment of "worm" infections, such as Enterobius vermicularis, Tichuris trichiura, and Ascaris lumbricoides. *Quinine choice: Quinine is an antimalarial agent indicated for the treatment of malaria and severe leg cramps. *TETRACYCLINE CHOICE: TETRACYCLINE IS AN ANTI-BACTGERIAL AGENT WITH A LIMITED ANTI-BACTERIAL SPECTRUM; IT IS PRIMARILY USED IN THE TREATMENT OF ACNE VULGARIS AND GONORRHEA INFECTIONS.
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Two weeks after birth, a neonate develops sepsis, skin vesicles, and conjunctivitis. Over the next several days, the baby's condition deteriorates with development of seizures, cranial nerve palsies, and lethargy. The baby dies approximately one week after onset of symptoms. Which of the following infectious agents would most likely cause this clinical presentation?
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Herpes simplex
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(Microbiology General Principles : 53%): CMV, RUBELLA, syphilis, and Toxoplasmosis choices: All of the agents listed can cause devastating congenital infections with high mortality and often with major organ malformation (the TORCH agents: T.oxoplasma, O.ther, R.ubella, C.ytomegalovirus, H.erpes simplex). However, it is herpes simlex type II, typically acquired during delivery, that causes the devastating neonatal encephalitis described in the question stem. The mortality rate for neonatal herpes is about 65% , and only 10% of the babies escape without neurologic sequelae. A point worth remembering is that adult herpes encephalitis (in non-immunosuppressed individuals) is usually due to herpes simplex I, while neonatal and congenital herpes are usually due to herpes simplex II.
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A 33-year-old woman begins seeing a new boyfriend. Several weeks later, a week after her menstrual period, the woman develops a painful, swollen right knee. The most likely causative organism has which of the following characteristics?
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Can live within neutrophils
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( Microbiology Musculoskeletal: 54%): The causative organism is Neisseria gonorrhoeae, which is a sexually transmitted gram-negative coccus that can live in phagocytic vacuoles in neutrophils and macrophages. The organism is the most common cause of septic arthritis in otherwise healthy, sexuall active adults. *Both hyphae and spores choice: Hyphae and spores would be features of Candida, which usually causes arthritis as a rare complication of systemic candidiasis in immunocompromised patients. *Cannot make ATP choice: The Chlamydia are intracellular organisms that cannot make ATP and do not usually cause septic arthritis. *NO TRUE CELL WALL CHOICE: MYCOPLASMA DO NOT HAVE TRUE CELL WALLS AND DO NOT USUALLY CAUSE SEPTIC ARTHRITIS. *Stains with silver stains choice: Syphilis is caused by a spirochete that stains with silver stains (as does Legionella). Secondary syphilis can (uncommmonly) cause an acute arthritis, but the interval between acquiring the infection and developing the arthritis is usually months to years.
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A 27-year-old woman has a pruritic linear, vesicular rash on her leg. The rash developed 16 hours after she returned from a hiking trip. It began as a swollen, erythematous streak that developed into extremely itchy bliasters. She goes on hiking and camping trips twice a year and has experienced similar episodes in the past. The rash is most likely a result of which of the following mechanisms?
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Release of lymphokines from sensitized lymphocytes
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(Immunology General Principles: 41%): This woman most likely has been exposed to poison ivy, which is followed by a contact, type IV cell-mediated, sensitivity response to urishiol, an oil found in poison ivy. Contact with this oil leads to a reaction that appears as a linear, streak-like rash in sensitized individuals. Redness, swelling, and pruritic blisters occur at the sites of contact. Sensitivity usually develops after the first contact with poison ivy, and the reaction described typically occurs following subsequent exposures. Antigenic activation of T lymphocytes and macrophages leads to the production of lymphokines, which produce the tissue injury. This reaction does not require the formation of antibodies. *Antigen-antibody complexes formed in the circulation and deposited in the tissue choice: Antigen-antibody complexes formed in the circulation and deposited in the tissue underlie type III hypersensitivity reactions. Diseases mediated by this type of hypersensitivity include systemic lupus erythematosus and most types of glomerulonephritis. *CYTOTOXIC ANTIBODIES AGAINST CELL SURFACE ANTIGENS: CYTOTOXIC ANTIBODIES AGAINST CELL SURFACE ANTIGENS PRODUCE TYPE II HYPERSENSITIVITY REACTIONS. DISEASES MEDIATED BY THIS TYPE OF HYPERSENSITIVITY INCLUDE AUTOIMMUNE HEMOLYTIC ANEMIA, PEMPHIGOID, PEMPHIGUS, AND GOODPASTURE DISEASE. *IgE antibody-mediated basophil degranulation and release of histamine from mast cell choices: IgE antibody-mediated basophil degranulation and the release of histamine from mast cells are the mechanisms responsible for type I immediate hypersensitivity reactions. IgE antibodies are formed in response to expsoure to a specific antigen. Reexposure to that antigen results in the production of additional IgE antibodies, which leads to mast cell and basophil degranulation and the syntehsis of additional mediators that cause the class manifestations of type I hypersensitivity reactions. Examples are hives, hay fever, and anaphylactic reactions.
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A 32-year-old female who is 6 months pregnant presents for prenatal care. A routine evaluation is performed, including testing for HIV antibody. The patient is reported to be negative for RPR, but positive for HIV antibody by the enzyme-linked immunoassay (EIA). The HIV Western blot is positive for antibody to the p24 antigen. The patient should be counseled:
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to have an HIV polymerase chain reaction (PCR) test performed
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( Immunology General Principles: 39%): A patient who is HIV EIA-positive must always have the result confirmed by a confirmatory assay (e.g., HIV Western blot). The HIV Western blot is considered positive when the patient demonstrates the presence of antibody to at least two of three important HIV antigens, which are gp120, gp41, and p24. If no reaction is observed, then the patient is considered negative, but any reaction that is not consistent with a positive is reported as indeterminate. Therefore, this patient is considered indeterminate. The physican can wait 6 months and retest by Western blot; if the results are identical, then the patient is reported as negative, or the patient can be tested by another confirmatory test, such as the PCR assay. A negative PCR in this situation would classify this patient as negative; however, it would be wise to retest the patient in 3-6 months if she had risk factors. *...that she and her baby were both infected with HIV choice: Approximately 30% of the babies from untreated and 8% from treated HIV-positive mothers will be infected. One cannot conclude from the available data that both she and her baby are infected. *...that she had a false-positive HIV EIA choice: It is possible that this patient had a false-positive HIV EIA assay, but with the present data, it is impossible to know if the patient is in the early stages of seroconversion or if the test result is a false positive. *...that she is negative for HIV since the RPR was negative choice: RPR is a test for syphilis (and not a very specific one at that), not a test for HIV *...THAT SHE IS POSITIVE FOR THE HIV VIRUS CHOICE: BECAUSE THIS PATIENT'S WESTERN BLOT WAS INDETERMINATE, A CONFIRMATORY TEST (E.G., WESTERN BLOT OR PCR) MUST BE PERFORMED TO DETERMINE WHETHER SHE IS TRULE POSITIVE FOR THE HIV VIRUS.
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A 57-year-old man presents with an episode of shaking chills the previous night. He has now developed right-sided pleuritic chest pain, fever, sweats, malaise, purulent sputum, and mild hemoptysis. On examination, the patient is diaphoretic but alert, with right basilar rales. Chest X-ray films show a right lower lobe infiltrate with blunting of the right costophrenic angle. Why is this patient's sputum filled with pus?
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Teichoic acids and peptidoglycan are chemotactic for neutrophils
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( Microbiology Respiratory: 38%): The answer to this question requires that the student realize that pus consists of bacteria and dead and dying neutrophils. This fact, taken along with the highly characterstic case history, reflects that the patient has a TYPICAL pneumonia. In the United States, the most common agent of this would be Streptococcus pneumoniae, a gram-positive extracellular pathogen rich in teichoic acids and peptidoglycan, which elicit the neutrophilic exudate. *THE CAPSULE OF THE CAUSATIVE AGENT IS CHEMOTACTIC FOR NEUTROPHILS CHOICE: THE CAPSULE OF THIS ORGANISM IS A POLYSACCHARIDE AND PRIMARILY ELICITS AN ANTIBODY RESPONSE RATHER THAN ATTRACTING NEUTROPHILS. *The causative agent is an intracellular organism choice: Streptococcus pneumoniae is an extracellular, not an intracellular organism. *The causative agent is beta hemolytic choice: Streptococcus pneumoniae is alpha hemolytic, not beta hemolytic. *The organism produces an IgA protease choice: Streptococcus pneumoniae does produce an IgA protease that enhances the ability of the organism to infect the respiratory mucosa, but this does not contribute to pus formation.
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A medical virology laboratory coinfects cells in a tissue culture flask with Influenza A (H3N2) and Influenza A (H1N1). The flask is incubated for 48 hours, and the progeny viruses are analyzed. Four distinct variants of Influenza A are isolated: H3N2, H1N1, H3N1, and H1N2. Which of the following viral attributes made the production of H3N1 and H1N2 variants possible?
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segmented genome
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(Microbiology General Principles: 52%): THIS IS ANOTHER INSTANCE WHERE I SHOULD HAVE TRUSTED MY GUT REACTION! Influenza A is well known for its ability to undergo genetic shift, or reassortment of the pieces of its segmented genome. Because the genome of this RNA virus occurs in 8 separate pieces, random rearrangements can occur when two related viruses infect a single cell. The packaging of the progeny viruses can then become drastically changed, and pandemics can result in the population due to the sudden appearance of new antigenic types. There have been 4 major pandemics of influenza since 1933. Genetic shift can only occur in viruses with segmented genomes (separate pieces of RNA that can be exchanged in the progeny). There are 4 families of viruses with segmented genomes: B.O.A.R.: B.unyavirus, O.rthomyxovirus, A.renavirus, and R.eovirus. (REASSORTMENT OF SEGMENTED GENOME:PANDEMICS:SHIFT) *Conjugation choice: Conjugation is the process of genetic exchange in bacteria that requires cell-to-cell contact. It does not occur in viruses. *HIGH MUTATIONAL RATE CHOICE: HIGH MUTATIONAL RATE IS A POTENTIAL CAUSE OF GENETIC DRIFT IN VIRUS INFECTIONS. ALTHOUGH GENETIC DRIFT DUE TO MUTATIONAL CHANGE CAN HAPPEN IN VIRTUALLY ANY REPRODUCING ORGANISM, IT IS BEST DESCRIBED AS A MECHANISM FOR CAUSING ANTIGENIC DRIFT IN THE HUMAN IMMUNODEFICIENCY VIRUS. (MUTATION:DRIFT:HIV) *Reverse transcriptase choice: Reverse transcriptase is not present in the influenza viruses. It is the enzyme produced by HIV and hepadna virus that causes the production of a DNA strand off of an RNA original. *Syncytia formation choice: Syncytia formation is the property of forming multinucleated giant cells during viral infection. Fusing one infected cell to the uninfected cell next door allows some viruses to move within the host without being exposed to immunologic products outside the cell. Syncytia formation is a common mechanism of immunological evasion in the herpes virus family and in respiratory syncytial virus infections.
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A newborn is infected in utero with an enveloped virus containing double-stranded DNA. The child develops petechiae, hepatosplenomegaly, and jaundice. Brain calcifications are detected on CT. With which of the following viruses is the newborn most likely infected?
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Cytomegalovirus
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(Microbiology Reproductive: 72%): YET ANOTHER INSTANCE WHERE I SHOULD HAVE TRUSTED MY GUT REACTION! I PUT THE RIGHT ANSWER INITIALLY BUT DOUBTED MYSELF! BAD! BAD! BAD! The most common agents causing congenital infection in the United States are cytomegalovirus, herpes simplex virus, and Treponema pallidium. Congenital cytomegalovirus infection, which occurs in 1% to 2% of all live birth in the U.S., results from transplacental acquisition of a primary or recurrent maternal infection. Most infections are asymptomatic, but about 5% will present with hepatosplenomegaly, periventricular brain calcification, petechial hemorrhages, and hydrops. Sensorineural deafness is a common manifestation in affected infants. Primary infection of the mother is strongly associated with more severe symptoms in affected infants. The mortality rate is 30%, and most of the survivors will have neurologic impairment. CMV infections in children and adults are often asymptomatic; however, the virus is responsible for 10% of infectious mononucleosis cases (characterized by an absence of sheep RBC agglutinins). CMV also causes serious disease in immunosuppressed patients, including bone marrow recipients and AIDS patients. Ganciclovir is the drug of choice, although foscarnet has also been used with some success. *Hepatitis B, C, and D choices: Infections with hepatitis viruses, if symptomatic, are characterized by jaundice, lethargy, failure to thrive, abdominal distention, clay-colored stools, and elevated transaminase levels. Hepatitis B is the only viral hepatitis agent that is recognized as an important cause of neonatal disease. The infection is usually acquired during the birth process; therapy includes hyperimmune human anti-hepatitis B serum followed by a few weeks later with active immunization with rHBsAg injections. *HERPES SIMPLEX CHOICE: HERPES SIMPLEX CAN ALSO INFECT THE NEONATE. THE HALLMARK OF INFECTION IS PAINFUL SKIN VESCILES (PRESENT IN 50% OF AFFECTED INFANTS); OTHER MANIFESTATIONS INCLUDE ENCEPHALITIS, PNEUMONIA, HEPATITIS, AND DISSEMINATED INTRAVASCULAR COAGULOPATHY. MASSIVE HEPATIC AND ADRENAL NECROSIS IS COMMON. THERAPY IS WITH ACYCLOVIR. (HSV:ACYCLOVIR)
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A 4-year-old child is brought into your clinic by his mother. A week ago, the child received an MMR vaccine, and now the child has an unusual rash, as show here. What is the most likely explanation for this occurrence?
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A latent infection in the child has been reactivated
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(Microbiology General Principles: 56%): The rash that is shown in the image is clearly unilateral and follows a dermatome, which is diagnostic of the rash of shingles, the second manifestation of infection with the Varicella zoster virus. Shingles can only occur following a primary infection with this virus, which would always be manifested as a case of chickenpox. It can only result following reactivation of a previously latent infection. *The child has been exposed to a child with chickenpox choice: Exposure of a "naive" individual to chickenpox would result in a case of chickenpox, which has different symptomatology from that described. *The child has been exposed to a grandparent with shingles choice: Expsoure of a "naive" individual to shingles would result in a case of chickenpox, which has a different symptomatology from that described. *The rash is a normal side effect of the MMR choice: MMR is an attenuated live virus vaccine against measles, mumps, and rubella. It does not have a constituent that would cause a shingles-like rash. *THE VACCINE WAS CONTAMINATED WITH LIVE VIRUS CHOICE: CONTAMINATION WITH LIVE VIRUS IS NOT A POSSIBILITY BECAUSE ANY CONTAMINATION WITH VARICELLA ZOSTER VIRUS WOULD HAVE RESULTED IN A CASE OF CHICKENPOX, NOT SHINGLES.
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