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162 Cards in this Set
- Front
- Back
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mycoses
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Human mycoses are caused by true fungal pathogens and opportunistic pathogens
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True or primary fungal pathogen
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True or primary fungal pathogen can invade and grow in a healthy, noncompromised host
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Thermal dimorphism
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Most striking adaptation to survival and growth in the human host is the ability to switch from hyphal cells to yeast cells
Thermal dimorphism – grow as molds at 30°C and as yeasts at 37°C |
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Epidemiology of the Mycoses
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Most fungal pathogens do not require a host to complete their life cycles and infections are not communicable
Dermaphytes and Candida sp naturally inhabit human body and are transmissible Cases go undiagnosed or misdiagnosed |
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Primary mycoses
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respiratory portal; inhaled spores
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Subcutaneous
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inoculated skin; trauma
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Cutaneous and superficial
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contamination of skin surface
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Control of Mycotic Infections
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Immunization is not usually effective
Control involves intravenous antibiotics In some cases surgical removal of damaged tissues Prevention limited to masks and protective clothing to reduce contact with spores |
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Systemic Infections by True Pathogens
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Restricted to endemic regions of the world
Infection occurs when matter containing conidia is disturbed Spores usually germinate in the lungs Spores may be inoculated into the skin Infection can become systemic |
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Histoplasmosis: Ohio Valley Fever
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Histoplasma capsulatum – most common true pathogen; causes histoplasmosis
Typically dimorphic Most prevalent in eastern and central regions of U.S. Grows in moist soil high in nitrogen content Inhaled conidia produce primary pulmonary infection that may progress to systemic involvement of a variety of organs and chronic lung disease Antibiotic treatment |
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Coccidioidomycosis: Valley Fever
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Coccidioides immitis – causes coccidioidomycosis
Distinctive morphology – blocklike arthroconidia in the free-living stage and spherules containing endospores in the lungs Lives in alkaline soils in semiarid, hot climates and is endemic to southwestern U.S. Arthrospores inhaled from dust, creates spherules, and can form nodules in the lungs Antibiotic treatment |
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Blastomyces Dermatitidis: North American Blastomycosis
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Blastomyces dermatitidis – causes blastomycosis
Dimorphic Free-living species distributed in soil of a large section of the midwestern and southeastern U.S. Inhaled 10-100 conidia convert to yeasts and multiply in lungs Symptoms include cough and fever Chronic cutaneous, bone, and nervous system complications Antibiotic treatment |
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Subcutaneous Mycoses
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Subcutaneous mycoses: when fungi are transferred directly into traumatized skin, they can invade
Most species in this group are greatly inhibited by higher temperatures of the blood and viscera Diseases are progressive |
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Sporothrix Schenckii
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Sporotrichosis (rose-gardener’s disease)
Very common saprobic fungus that decomposes plant matter in soil Infects appendages and lungs Lymphocutaneous variety occurs when contaminated plant matter penetrates the skin and the pathogen forms a nodule, then spreads to nearby lymph nodes |
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Mycetoma
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When soil microbes are accidentally implanted into the skin
Progressive, tumor-like disease of the hand or foot due to chronic fungal infection; may lead to loss of body part |
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Cutaneous Mycoses
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Infections strictly confined to keratinized epidermis (skin, hair, nails) are called dermatophytoses – ringworm and tinea
39 species in the genera Trichophyton, Microsporum, Epidermophyton Closely related and morphologically similar Causative agent of ring worm varies case to case |
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(tinea capitis)
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Ringworm of scalp affects scalp and hair-bearing regions of head; hair may be lost
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(tinea barbae)
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Ringworm of beard affects the chin and beard of adult males; contracted mainly from animals
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(tinea corporis)
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Ringworm of body occurs as inflamed, red ring lesions anywhere on smooth skin
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(tinea cruris)
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Ringworm of groin “jock itch” affects groin and scrotal regions
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(tinea pedis and tinea manuum)
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Ringworm of foot and hand is spread by exposure to public surfaces; occurs between digits and on soles
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(tinea unguium)
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Ringworm of nails is a persistent colonization of the nails of the hands and feet that distorts the nail bed
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Treatment of dermatophytes
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includes topical antifungal agents applied for several weeks
Lamisil or griseofulvin 1-2 years |
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Superficial Mycoses
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Tinea versicolor
White piedra Black piedra |
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Tinea versicolor
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elicits mild, chronic scaling, mottling of skin; also implicated in folliculitis, psoriasis, and seborrheic dermatitis
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White piedra
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whitish or colored masses develop scalp, pubic, or axillary hair
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Black piedra
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dark-brown to black gritty nodules, mainly on scalp hairs
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Opportunistic Mycoses
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All have predisposing factors
Candida – dominant opportunistic pathogen Aspergillus – accounts for most lung infections Cryptococcus |
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Infections by Candida: Candidiasis
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Candida albicans
Widespread yeast Infections can be short-lived, superficial skin irritations to overwhelming, fatal systemic diseases Budding cells of varying size that may form both elongate pseudohyphae and true hyphae Forms off-white, pasty colony with a yeasty odor |
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Candida Albicans
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Normal flora of oral cavity, genitalia, large intestine or skin of 20% of humans
Account for 70% of nosocomial fungal infections Thrush – occurs as a thick, white, adherent growth on the mucous membranes of mouth and throat Vulvovaginal yeast infection – painful inflammatory condition of the female genital region that causes ulceration and discharge Cutaneous candidiasis – occurs in chronically moist areas of skin and in burn patients |
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Cryptococcosis and Cryptococcus Neoformans
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Cryptococcus neoformans causes cryptococcosis
A widespread encapsulated yeast that inhabits soil around pigeon roosts Common infection of AIDS, cancer, or diabetes patients Infection of lungs leads to cough, fever, and lung nodules Dissemination to meninges and brain can cause severe neurological disturbance and death |
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Pneumocystis (Carinii) Jiroveci and Pneumocystis Pneumonia
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A small, unicellular fungus that causes pneumonia (PCP), the most prominent opportunistic infection in AIDS patients
This pneumonia forms secretions in the lungs that block breathing and can be rapidly fatal if not controlled with medication Antibiotic treatment |
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Aspergillosis: Diseases of the Genus Aspergillus
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Very common airborne soil fungus
600 species, 8 involved in human disease; A. fumigatus most commonly Serious opportunistic threat to AIDS, leukemia, and transplant patients Infection usually occurs in lungs – spores germinate in lungs and form fungal balls; can colonize sinuses, ear canals, eyelids, and conjunctiva Invasive aspergillosis can produce necrotic pneumonia, and infection of brain, heart, and other organs Antibiotic treatment |
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Zygomycosis
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Zygomycota are extremely abundant saprobic fungi found in soil, water, organic debris, and food
Genera most often involved are Rhizopus, Absidia, and Mucor Usually harmless air contaminants invade the membranes of the nose, eyes, heart, and brain of people with diabetes and malnutrition, with severe consequences |
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Fungal Allergies and Intoxications
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Fungal spores are common sources of atopic allergies
Seasonal allergies and asthma Farmer’s lung, teapicker’s lung, bark stripper’s disease |
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Stachybotrys chartarum
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sick building syndrome; severe hematologic and neurological damage
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Aflatoxin
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toxic and carcinogenic; grains, corn, peanuts; lethal to poultry and livestock
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mycotoxicoses
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Fungal toxins lead to mycotoxicoses usually caused by ingesting or inhaling fungal toxins
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Typical Protozoan Pathogens
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Single-celled, animal-like microbes, most having some form of motility
Life cycles vary Most propagate by simple asexual cell division of the active feeding cell (trophozoite) Many undergo formation of a cyst Others have a complex life cycle that includes asexual and sexual phases |
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Infective Amebas
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Entamoeba Histolytica
Naegleria fowleri Acanthamoeba |
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Entamoeba Histolytica and Amebiasis
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Humans are the primary hosts
Ingested Carried by 10% of world population, 90% asymptomatic Causing dysentery, abdominal pain, fever, diarrhea, and weight loss Life-threatening manifestations are: hemorrhage, perforation, appendicitis, and tumorlike growths Antibiotics are effective |
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Amebic Infections of the Brain
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Caused by Naegleria fowleri and Acanthamoeba
Ordinarily inhabit standing water Primary acute meningoencephalitis is acquired through nasal contact with water or traumatic eye damage Infiltration of brain is usually fatal |
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Infective ciliates
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Balantidium Coli
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An Intestinal Ciliate: Balantidium Coli
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An occupant of the intestines of domestic animals such as pigs and cattle
Acquired by ingesting cyst-containing food or water Trophozoite erodes intestine and elicits intestinal symptoms Healthy humans are resistant Rarely penetrates intestine or enters blood Treatment - Antibiotics |
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Infective Flagellates
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Trichomonas vaginalis
Giardia Lamblia Trypanosoma Cruzi |
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Trichomonads: Trichomonas Species
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Small, pear-shaped
4 anterior flagella and an undulating membrane Exist only in trophozoite form 3 infect humans: T. vaginalis T. tenax T. hominis |
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Trichomonas Vaginalis
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Causes an STD called trichomoniasis
Reservoir is human urogenital tract 50% of infected are asymptomatic Strict parasite, cannot survive long outside of host 3 million cases yearly, a top STD Female symptoms – foul-smelling, green-to-yellow discharge; vulvitis; cervicitis; urinary frequency and pain Male symptoms – urethritis, thin, milky discharge, occasionally prostate infection Antibiotic treatment |
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Giardia Lamblia and Giardiasis
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Pathogenic flagellate
Unique symmetrical heart shape with concave ventral surface that acts like a suction cup Cysts are small, compact, and multinucleate Reservoirs include beavers, cattle, coyotes, cats, and humans Cysts can survive for 2 months in environment Usually ingested with water and food ID 10 to 100 cysts Treated with antibiotics |
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Hemoflagellates: Vector-Borne Blood Parasites
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Obligate parasites that live in blood and tissues of human host
Cause life-threatening and debilitating zoonoses Spread in specific tropical regions by blood-sucking insects that serve as intermediate hosts Have complicated life cycles and undergo morphological changes Categorized according to cellular and infective stages |
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Hemoflagellates
Amastigote |
the form lacking a free flagellum
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Hemoflagellates
Promastigote |
the stage bearing a single, free, anterior flagellum
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Hemoflagellates
Epimastigote |
the flagellate stage
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Hemoflagellates
Trypomastigote |
large, fully formed stage
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trypomastigote
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Distinguished by their infective stage; trypomastigote is an elongate, spindle-shaped cell with tapered ends, eel-like motility
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Trypanosoma Cruzi
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Causes Chagas disease
Reduviid bug (kissing bug) is the vector Infection occurs when bug feces is inoculated into a cutaneous portal Local lesion, fever, and swelling of lymph nodes, spleen, and liver Heart muscle and large intestine harbor masses of amastigotes Chronic inflammation occurs in the organs (especially heart and brain) Antibiotic treatment |
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Apicomplexan Parasites
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Sporozoans
Lack locomotor organelles in the trophozoite state Alternate between sexual and asexual phases and between different animal hosts Most form specialized infective bodies that are transmitted by arthropod vectors, food, water, or other means Plasmodium Toxoplasma Cryptosporidium |
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Plasmodium: The Agent of Malaria
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Dominant protozoan disease
Obligate intracellular sporozoan 4 species: P. malariae, P. vivax, P. falciparum, and P. ovale Female Anopheles mosquito is the primary vector; blood transfusions, mother to fetus 300-500 million new cases each year 2 million deaths each year |
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2 distinct phases of malarial parasite development
Asexual phase |
human host
Infected female mosquito injects asexual sporozoite which localizes in liver; it then undergoes schizogony generating numerous merozoites which enter circulation in 5-16 days depending on species Merozoites attach to and enter red blood cells, convert to trophozoites and multiply; red cell bursts releasing merozoites that differentiate into gametes |
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2 distinct phases of malarial parasite development
Sexual phase |
mosquito host
Mosquito draws infected RBCs; gametes fertilize forming diploid cell which forms sporozoites in stomach Sporozoites lodge in salivary glands; available to infect human host |
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Plasmodium
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Symptoms include episodes of chills-fever-sweating, anemia, and organ enlargement
Symptoms occur at 48-72 hour intervals as RBCs rupture; interval depends on species P. falciparum most malignant type; highest death rate in children Diagnosis by presence of trophozoite in RBCs, symptoms Increasing drug resistance |
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Coccidian Parasites
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Zoonotic in domestic animals and birds
Single celled parasites that infect intestines |
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Toxoplasma Gondii and Toxoplasmosis
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Intracellular apicomplexan parasite with extensive distribution
Lives naturally in cats that harbor oocysts in the GI tract Acquired by ingesting raw meats or substances contaminated by cat feces Most cases of toxoplasmosis go unnoticed except in fetus and AIDS patients who can suffer brain and heart damage Treatment: pyrimethamine and sulfadiazine |
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Babesia Species and Babesiosis
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First protozoan found to cause a disease – redwater fever of cattle
First protozoan found to be associated with a vector – tick Human babesiosis – relatively rare zoonosis Associated with infected rodents Infection resembles malaria |
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A Survey of Helminth Parasites
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Adults are large, multicellular animals with specialized tissues and organs
Adult worms mate and produce fertilized eggs that hatch; larvae then mature in several stages to adults The sexes may be separate or hermaphroditic Adulthood and mating occur in the definitive host Larval develop occurs in the intermediate host A transport host experiences no parasitic development Four basic patterns of life and transmission |
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Helminths
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Pathology arises from worms feeding on and migrating through tissues, accumulation of worms, and worm products
Diagnosis based on blood cell count (eosinophilia), serological tests; eggs, larvae, or adult worms in feces; sputum, urine, blood, or tissue biopsies |
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Antihelminthic drugs
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suppress a helminthic metabolic process that differs from the human process, inhibit the worm’s movement, prevent it from holding position, and act locally in the intestine
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Nematode (Roundworm) Infestations
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Ascaris Lumbricoides
Enterobius Vermicularis Necator americanus Ancylostoma duodenale Trichinella Spiralis |
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Ascaris Lumbricoides
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A large intestinal roundworm
Most cases in the U.S. occur in the southeastern states Indigenous to humans Ascaris spends its larval and adult stages in humans; release embryonic eggs in feces, and are spread to other humans; food, drink, or contaminated objects Ingested eggs hatch into larvae and burrow through the intestine into circulation and travel to the lungs and pharynx and are swallowed Allergic reactions can occur Heavy worm loads can retard physical and mental development |
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Enterobius Vermicularis and Pinworm Infection
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Pinworm or seatworm
Most common worm disease of children in temperate zones Eggs are picked up from surroundings and swallowed After hatching in the small intestine, they develop into adults Anal itching occurs when mature females emerge from intestine to release eggs Self-inoculation is common |
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Hookworms
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Characteristic curved ends and hooked mouths
Necator americanus and Ancylostoma duodenale Humans shed eggs in feces, which hatch into filariform larvae and burrow into the skin of bare feet Larvae travel from blood to lungs, proceed up bronchi and throat and are swallowed Worms mature and reproduce in small intestine and complete the cycle May cause pneumonia, nausea, vomiting, cramps, and bloody diarrhea Blood loss is significant – anemia |
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Trichinella Spiralis and Trichinellosis
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Life cycle entirely within mammalian host
Acquired from eating undercooked pork or bear meat Larvae migrate from intestine to blood vessels, muscle, heart, and brain, where it forms cysts First symptoms – flulike, diarrhea Second symptoms – muscle and joint pain, shortness of breath, pronounced eosinophilia No cure after larva have encysted |
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Trematodes or Flukes
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Schistosomes
Opisthorchis (Clonorchis) sinensis Fasciola hepatica Paragonimus westermani |
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Trematodes or Flukes
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Flatworms with ovoid leaflike bodies
Animals such as snails or fish are usually the intermediate hosts and humans are the definitive hosts |
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Blood Flukes: Schistosomes
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Schistosomiasis – prominent parasitic disease
Adult flukes live in humans who release eggs into water; early larva (miracidium) develops in freshwater snail into a 2nd larva (cercaria) This larva penetrates human skin and moves into the liver to mature; adults migrate to intestine or bladder and shed eggs, giving rise to chronic organ enlargement |
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Lung Flukes
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Zoonotic
Liver flukes: Opisthorchis (Clonorchis) sinensis – cycles between mammals and snails and fish; humans are infected by eating inadequately cooked fish containing cercariae, larvae crawl into bile duct, mature, and shed eggs into feces; snail are infected Fasciola hepatica – cycles between herbivores, snails, and aquatic plants; humans are infected by eating raw aquatic plants; fluke lodges in liver |
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Liver Flukes
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Paragonimus westermani – cycles between carnivorous animals, snails, and crustaceans; humans infected by eating undercooked crustaceans; intestinal worms migrate to lungs
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Cestode (Tapeworm) Infestations
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Flatworms
Long, very thin, ribbonlike bodies composed of sacs (proglottids) and a scolex that grips the intestine Each proglottid is an independent unit adapted to absorbing food and making and releasing eggs |
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Beef Tapeworm
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Beef tapeworm
Humans are the definitive host Animals are infected by grazing on land contaminated with human feces Infection occurs from eating raw beef in which the larval form has encysted In humans, larva attaches to the small intestine and becomes an adult Causes few symptoms; vague abdominal pain and nausea; proglottids in stool |
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Pork Tapeworm
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Pork tapeworm
Infects humans through ingesting cysts or eggs Eggs hatch in intestine, releasing tapeworm larva that migrate to all tissues and encyst Most damaging if they lodge in heart muscle, eye, or brain May cause seizures, psychiatric disturbances |
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Enveloped DNA Viruses
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Poxviruses
Herpesviruses Hepadnaviruses |
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Poxviruses: Classification and Structure
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Produce eruptive skin pustules called pocks or pox, that leave scars
Largest and most complex animal viruses Have the largest genome of all viruses dsDNA Specificity for cytoplasm of epidermal cells and subcutaneous connective tissues |
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Smallpox
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First disease to be eliminated by vaccination
Exposure through inhalation or skin contact Infection associated with fever, malaise, prostration, and a rash |
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Smallpox Control
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Routine vaccination ended in U.S. in 1972
Vaccine reintroduced in 2002 for military and medical personnel |
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Molluscum Contagiosum
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In endemic areas, it is primarily an infection of children
Transmitted by direct contact and fomites In U.S., most commonly an STD Lesions are small, smooth macules in genital area and thighs AIDS patients suffer an atypical form which attacks the skin of the face and forms tumor-like growths Treatment: freezing, electric cautery, chemical agents |
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Monkeypox in humans
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skin pocks, fever, swollen lymph nodes
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Cowpox in humans
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rare, usually confined to hands; other cutaneous sites can be involved
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The Herpesviruses: Common, Persistent Human Viruses
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All members show latency and cause recurrent infection
Clinical complications of latency and recurrent infections become more severe with advancing age, cancer chemotherapy, or other conditions that compromise the immune defenses Common and serious opportunists among AIDS patients |
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Herpes Simplex Viruses
HSV-1 |
usually lesions on the oropharynx, cold sores, fever blisters
Occurs in early childhood |
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Herpes Simplex Viruses
HSV-2 |
lesions on the genitalia, possibly oral
Occurs in ages 14-29 Can be spread without visible lesions |
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Herpes labialis
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fever blisters, cold sores; most common recurrent HSV-1 infection; vesicles occur on mucocutaneous junction of lips or adjacent skin; itching and tingling prior to vesicle formation; lesion crusts over in 2-3 days and heals
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Herpetic gingivostomatitis
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infection of oropharynx in young children; fever, sore throat, swollen lymph nodes
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Herpetic keratitis
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ocular herpes – inflammation of eye; gritty feeling in the eye, conjunctivitis, sharp pain, and sensitivity to light
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Type 2 Herpes Infections
Genital herpes |
herpes genitalia – starts with malaise, anorexia, fever, and bilateral swelling and tenderness in the groin; clusters of sensitive vesicles on the genitalia, perineum, and buttocks; urethritis, painful urination, cervicitis, itching; vesicles ulcerate
Recurrent bouts usually less severe, triggered by menstruation, stress, and concurrent bacterial infection |
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Type 2 Herpes Infections
Herpes of the Newborn |
HSV-1 and HSV-2
Potentially fatal in the neonate and fetus Infant contaminated by mother before or during birth; hand transmission by mother to infant Infection of mouth, skin, eyes, CNS Preventative screening of pregnant women; delivery by C-section if outbreak at the time of birth |
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Herpetic whitlow
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HSV-1 or HSV-2 can penetrate a break in the skin and cause a localized infection; usually on one finger; extremely painful and itchy
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HSV-1 encephalitis
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rare complication but most common sporadic form of viral encephalitis in the U.S.
Those with underlying immunodeficiency are prone to severe, disseminated herpes |
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Varicella-Zoster Virus (VZV)
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Causes chickenpox and shingles
Humans only natural host Transmitted by respiratory droplets and contact Primary infection – chickenpox – characteristic vesicles Virus enters neurons and remains latent |
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Cytomegalovirus
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Newborns may exhibit enlarged liver and spleen, jaundice, capillary bleeding, microcephaly, and ocular inflammation; may be fatal
Babies who survive develop neurological sequelae, hearing, visual disturbances and mental retardation Perinatal CMV infection – mostly asymptomatic, or pneumonitis, and a mononucleosis-like syndrome AIDS patients – CMV mononucleosis, disseminated CMV, retinitis Transplant patients – pneumonitis, hepatitis, myocarditis, meningoencephalitis Treatment reserved for immunocompromised – ganciclovir, foscarnet |
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Epstein-Barr Virus (EBV)
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Ubiquitous virus; infects lymphoid tissue and salivary glands
Transmission – direct, oral contact and contamination with saliva In industrialized countries, college-age population is vulnerable to infectious mononucleosis (mono or kissing disease) By mid-life, 90-95% of all people are infected Anyone with an immune deficiency is highly susceptible to EBV |
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Epstein-Barr Virus (EBV)
Infectious mononucleosis |
sore throat, high fever, cervical lymphadenopathy; develop after 30-50 day incubation
Dormancy in B cells; reactivated; may be asymptomatic |
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Tumors and Other Complications Associated with EBV
Burkitt lymphoma |
B cell malignancy; usually develops in jaw and grossly swells the cheek; central African children 4-8 years old; may be associated with chronic coinfections with malaria, etc.
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Tumors and Other Complications Associated with EBV
Nasopharyngeal carcinoma |
malignancy of epithelial cells; occurs in older Chinese and African men
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Hepatitis
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an inflammatory disease of liver cells that may result from several viruses
Interferes with liver’s excretion of bile pigments, bilirubin accumulates in blood and tissues causing jaundice, a yellow tinge in skin and eyes |
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Hepadnaviruses
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Enveloped DNA viruses
Never been grown in tissue culture Unusual genome containing both double- and single-stranded DNA Tropism for liver |
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Hepatitis B Virus and Disease
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Multiplies exclusively in the liver, which continuously seeds blood with viruses – chronic
Minute amounts of blood, blood products can transmit infection; sexually transmitted High incidence among homosexuals and drug addicts Can become a chronic infection Increases risk of liver cancer – hepatocellular carcinoma |
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Nonenveloped DNA Viruses
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Adenoviruses
Papillomaviruses Parvoviruses |
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The Adenoviruses
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Infect lymphoid tissue, respiratory and intestinal epithelia and conjunctiva
Spread by respiratory and ocular secretions Causes colds, pharyngitis, conjunctivitis, keratoconjunctivitis, acute hemorrhagic cystitis |
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Papilloma and Polyoma Viruses
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Small, nonenveloped dsDNA
Circular DNA Cause persistent infections and tumors |
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Human Papillomavirus
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Papilloma – squamous epithelial growth, wart, or verruca
Caused by 100 different strains of HPV Transmissible through direct contact or contaminated fomites; incubation – 2 weeks to more than a year Most common warts regress over time; they can be removed by direct chemical application of podophyllin and physical removal by cauterization, freezing, or laser surgery Warts can recur |
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Human Papillomavirus
Common seed warts |
painless, elevated, rough growth; on fingers, etc.
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Human Papillomavirus
Plantar warts |
deep, painful; on soles of feet
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Human Papillomavirus
Genital warts |
most common STD in U.S.; morphology ranges from tiny, flat, inconspicuous bumps to extensive, branching, cauliflower-like masses
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Human Parvoviruses
B19 |
cause of erythema infectiosum (fifth disease); rash of childhood
Children may have fever and rash on cheeks Severe fatal anemia can result if pregnant woman transmits virus to fetus |
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Human Parvoviruses
Adeno-associated virus |
(AAV) is a defective virus; it cannot replicate in host cell without adenovirus
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Enveloped Segmented Single-Stranded RNA Viruses
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Orthomyxoviruses
Bunyaviruses |
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The Biology of Orthomyxoviruses: Influenza
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Virus attaches to, and multiplies in, the cells of the respiratory tract
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Hemagglutinin
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(H) 15 different subtypes; most important virulence factor; binds to host cells
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Neuraminidase
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(N) – 9 subtypes – hydrolyzes mucus and assists viral budding and release
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Key to influenza are
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glycoprotein spikes
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antigenic drift
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Constant mutation is called antigenic drift – gradually change their amino acid composition
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Antigenic shift
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one of the genes or RNA strands is substituted with a gene or strand from another influenza virus from a different animal host
Genome of virus consists of 10 genes encoded on 8 separate RNA strands |
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Influenza B
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Only undergo antigenic drift
Not known to undergo antigenic shift |
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Influenza C
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Known to cause only minor respiratory disease; probably not involved in epidemics
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Influenza A
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Acute, highly contagious respiratory illness
Seasonal, pandemics; among top 10 causes of death in U.S. – most commonly among elderly and small children Binds to ciliated cells of respiratory mucosa Causes rapid shedding of cells, stripping the respiratory epithelium; severe inflammation Fever, headache, myalgia, pharyngeal pain, shortness of breath, coughing |
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Bunyaviruses and Arenaviruses
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Transmitted zoonotically; cause periodic epidemics; extremely dangerous; biosafety level 4 viruses
Bunyaviruses – transmitted by insects and ticks California encephalitis, Rift Valley fever, Korean hemorrhagic fever American bunyavirus is a hantavirus, Sin Nombre – emerging disease; high fever, lung edema, and pulmonary failure; 33% mortality rate Carried by deer and harvest mice; transmitted via airborne dried animal waste |
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Mumps
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Epidemic parotitis; self-limited, associated with painful swelling of parotid salivary glands
Humans are the only reservoir 40% of infections are subclinical; long-term immunity 300 cases in U.S./year Incubation 2-3 weeks fever, muscle pain and malaise, classic swelling of one or both cheeks Usually uncomplicated invasion of other organs; in 20-30% of infected adult males, epididymis and testes become infected; sterility is rare Symptomatic treatment Live attenuated vaccine MMR |
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Measles
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Caused by Morbillivirus
Also known as red measles and rubeola Different from German measles Very contagious; transmitted by respiratory aerosols Humans are the only reservoir Less than 100 cases/yr in U.S.; frequent cause of death worldwide |
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subacute sclerosing panencephalitis (SSPE),
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Most serious complication is subacute sclerosing panencephalitis (SSPE), a progressive neurological degeneration of the cerebral cortex, white matter, and brain stem
1 case in a million infections Involves a defective virus spreading through the brain by cell fusion and destroys cells Leads to coma and death in months or years Attenuated viral vaccine MMR |
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Respiratory Syncytial Virus (RSV)
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Also called Pneumovirus
Infects upper respiratory tract and produces giant multinucleate cells Most prevalent cause of respiratory infection in children 6 months or younger; most susceptible to serious disease Epithelia of nose and eye portal of entry; replicates in nasopharynx Fever, rhinitis, pharyngitis, otitis, croup |
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Rabies
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Rhabdovirus family; genus Lyssavirus
Virus enters through bite, grows at trauma site for a week and multiplies, then enters nerve endings and advances toward the ganglia, spinal cord and brain Infection cycle completed when virus replicates in the salivary glands |
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Rabies
Clinical phases of rabies |
Prodromal phase – fever, nausea, vomiting, headache, fatigue; some experience pain, burning, tingling sensations at site of wound
Furious phase – agitation, disorientation, seizures, twitching, hydrophobia Dumb phase – paralyzed, disoriented, stuporous Progress to coma phase, resulting in death |
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Severe Acute Respiratory Syndrome-Associated Coronavirus (SARS)
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Newly emerging disease – 2002
Transmitted through droplet or direct contact Fever, body aches, and malaise May or may not experience respiratory symptoms with breathing problems; severe cases can result in respiratory distress and death Diagnosis relies on exclusion of other likely agents Treatment is supportive |
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Rubella
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Caused by Rubivirus, a Togavirus
German measles No specific treatment available Attenuated viral vaccine MMR |
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Postnatal rubella
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malaise, fever, sore throat, lymphadenopathy, rash, generally mild, lasting about 3 days
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Congenital rubella
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infection during 1st trimester most likely to induce miscarriage or multiple defects such as cardiac abnormalities, ocular lesions, deafness, mental and physical retardation
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Hepatitis C Virus (HCV)
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Flavivirus
Acquired through blood contact – blood transfusions, needle sharing by drug abusers Infections with varying characteristics – 75-85% will remain infected indefinitely; possible to have severe symptoms without permanent liver damage; more common to have chronic liver disease, without overt symptoms Cancer may also result from chronic HCV infection Treatment with interferon and ribavirin to lessen liver damage; no cure No vaccine |
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Arboviruses: Viruses Spread by Arthropod Vectors
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Mosquitoes, ticks, flies, and gnats
400 viruses Togaviruses, flaviviruses, some bunyaviruses and reoviruses Most illnesses caused by these viruses are mild fevers; some may cause severe encephalitis, and life-threatening hemorrhagic fever |
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Viral encephalitis
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brain, meninges, and spinal cord are involved; convulsions, tremor, paralysis, loss of coordination, memory deficits, changes in speech and personality, coma; survivors may experience permanent brain damage
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Colorado tick fever (CTF)
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most common tick-borne viral fever in U.S.; Rocky Mountain states
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Western equine encephalitis (WEE)
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western U.S. and Canada; extremely dangerous to infants and small children
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Eastern equine encephalitis (EEE)
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eastern U.S. and Canada
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California encephalitis
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2 different strains:
California strain – western states; little human impact LaCrosse strain – eastern U.S. and Canada; prevalent cause of viral encephalitis |
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St. Louis encephalitis (SLE)
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most common of all in America; epidemics in midwestern and southern states; inapparent infections are very common
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West Nile encephalitis
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Arbovirus Infections in the USA
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Hemorrhagic Fevers
Yellow fever |
eliminated in U.S.
Two patterns of transmission: Urban cycle – humans and mosquitoes, Aedes aegypti Sylvan cycle – forest monkeys and mosquitoes; South America Acute fever, headache, muscle pain; may progress to oral hemorrhage, nosebleed, vomiting, jaundice, and liver and kidney damage; significant mortality rate |
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Hemorrhagic Fevers
Dengue fever |
flavivirus carried by Aedes mosquito; not in U.S.; usually mild infection
Dengue hemorrhagic shock syndrome, breakbone fever – extreme muscle and joint pain; can be fatal |
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HIV Infections and AIDS
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Human immunodeficiency virus
Acquired immunodeficiency syndrome First emerged in early 1980s HIV-1 may have originated from a chimpanzee virus 1959 first documented case of AIDS |
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Causative Agent AIDS
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HIV-1 and HIV-2
T-cell lymphotropic viruses I and II – leukemia and lymphoma HIV can only infect host cells that have the required CD4 marker plus a coreceptor |
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Epidemiology of HIV Infections
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Transmission occurs by direct and specific routes: mainly through sexual intercourse and transfer of blood or blood products; babies can be infected before or during birth, and from breast feeding
HIV does not survive long outside of the body First nationally notifiable in 1984 IV drug abusers can be HIV carriers; significant factor in spread to heterosexual population |
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Pathogenesis and Virulence Factors
AIDS |
HIV enters through mucous membrane or skin and travels to dendritic phagocytes beneath the epithelium, multiplies, and is shed
Virus is taken up and amplified by macrophages in the skin, lymph organs, bone marrow, and blood HIV attaches to CD4 and coreceptor; HIV fuses with cell membrane Reverse transcriptase makes a DNA copy of RNA Viral DNA is integrated into host chromosome Can produce a lytic infection or remain latent |
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Effects of HIV
Primary effects of HIV infection: |
Extreme leukopenia – lymphocytes in particular
Formation of giant T cells and other syncytia allowing the virus to spread directly from cell to cell Infected macrophages release the virus in central nervous system, with toxic effect, inflammation |
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Effects of HIV
Secondary effects of HIV: |
Destruction on CD4 lymphocytes allows for opportunistic infections and malignancies
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Signs and Symptoms of HIV Infections and AIDS
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Symptoms of HIV are directly related to viral blood level and level of T cells
Initial infection – mononucleosis-like symptoms that soon disappear Asymptomatic phase 2-15 years (avg. 10) HIV destroys the immune system When T4 cell levels fall below 200/mL, AIDS symptoms appear including fever, swollen lymph nodes, diarrhea, weight loss, neurological symptoms, opportunistic infections, and cancers |
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Diagnosis of AIDS
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Positive for the virus, and
They fulfill one of the additional criteria: They have a CD4 count of fewer than 200 cells/ml of blood Their CD4 cells account for fewer than 14% of all lymphocytes They experience one or more of a CDC-provided list of AIDS-defining illnesses |
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Preventing and Treating HIV
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No vaccine available
Monogamous sexual relationships Condoms Universal precautions No cure; therapies slow down the progress of the disease or diminish the symptoms Inhibit viral enzymes: reverse transcriptase, protease, integrase Inhibit fusion Inhibit viral integration Highly active anti-retroviral therapy |
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Poliomyelitis (polio)
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acute enteroviral infection of the spinal cord that can cause neuromuscular paralysis
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Poliovirus
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naked capsid; resistant to acid, bile, and detergents; can survive stomach acids when ingested
Worldwide vaccination programs have reduced the number of cases; eradication is expected |
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Pathogenesis of Poliomyelitis
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Transmitted by fecal-oral route
Polioviruses adhere to receptors of mucosal cells in oropharynx and intestine, multiply in number and shed in throat and feces, some leak into blood Most infections are short-term, mild viremia |
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Pathogenesis of Poliomyelitis
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Some develop mild nonspecific symptoms of fever, headache, nausea, sore throat, and myalgia
If viremia persists, virus spreads to spinal cord and brain If nervous tissue is infected but not destroyed – muscle pain and spasm, meningeal inflammation, and vague hypersensitivity |
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Hepatitis A Virus and Infectious Hepatitis
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Cubical picornavirus relatively resistant to heat and acid
Not carried chronically, principal reservoirs are asymptomatic, short-term carriers or people with clinical disease Fecal-oral transmission; multiplies in small intestine and enters the blood and is carried to the liver Most infections subclinical or vague, flu-like symptoms occur; jaundice is seldom present |
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Human Rhinovirus (HRV)
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Many strains circulating in the population at one time; acquired from contaminated hands and fomites
Sensitive to acidic environments; optimum temperature is 33oC Headache, chills, fatigue, sore throat, cough, nasal drainage Treat the symptoms Handwashing and care in handling nasal secretions |
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Norwalk agent
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believed to cause 1/3rd of all viral gastroenteritis cases
Transmitted by fecal-oral route Acute onset, nausea, vomiting, cramps, diarrhea, chills Rapid and complete recovery |
