Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
18 Cards in this Set
- Front
- Back
Major points:
Disease result of - "classic" dimorphism = Protective Host immune response - Latency - Determine exposure by - Disease more severe when? Transmission ISN'T - Lab mold cultures - |
spore inhalation
Environmental form = mold Tissue form = yeast or specialized Cell mediated immunity - CD4 cells generated against fungus -> activate phagocytic cells -> macrophages activated to fuse and "wall off" fungi (granuloma formation) THEREFORE: immune compromised host may not wall off infection and fungi will spread Infection may become latent and by the formation of granulomas (like TB) DTH skin test In the presence of HIV infection transmission is NOT person to person these cultures are very hazardous |
|
Histoplasma capsulatum
Clincal significance: (distribution, endemic areas, severity of infection) |
wide distrib - temperate, subtropical and tropical
highly endemic to Ohio and Mississippi valley regions <1% become progressive and require therapy |
|
Pathogen Properties
growth: structural characteristics: Virulence factor: |
dimorphic growth - environment hyphal/mycelial form, infected tissue yeast form
Hyphae - septate, branching, spores (microconidia and macroconidia) Yeast - ovoid, found within macrophages, capsular appearance is just an artifact of staining Virulence - can grow inside macrophages, surviving in phagocytic vacuole |
|
Pathogenesis:
|
Inhaled spores (micro) -> small brochioles or alveoli -> germinate after 2-3 days -> proliferate within macrophages -> migrate to mediastinal lymph nodes, spleen, liver -> prolif for 9-15 days -> onset host immune response
yeast usually found inside macrophages, can be found extracellularly and in epithelial cells |
|
Infections:
|
Acute pulmonary histoplasmosis - in immunocompetent hosts
Disseminated histoplasmosis - rare and severe, found with AIDS Chronic Pulmonary Histoplasmosis - opportunistic, often mistaken for tuberculosis Colonization in abnormal pulmonary spaces - allowed by Lung structural defects |
|
Diagnosis:
|
Histoplasmin skin test indicated exposure to organism, not necessarily infection
Fungal stain of tissue, ID in lab cultures on special media, demonstrated dimorphism and tissue form, exoantigen tests to demonstrate specific Ags to mycelial cultures Wright stain blood smear - look for intracellular yeasts in macroph Chest X-ray, CF test, sputum culture, wright stain of sputum contribute to diagnosis of chronic pulmonary histo |
|
Prevention:
Treatment: |
avoid envir exposure
antifungal therapy for disseminated disease |
|
Blastomyces dermatitidis
Clinical significance: |
mainly occurs as sporadic infection in immunocompromised hosts
Epidemics and cases noted in AIDS patients and immunocomp hosts Cell-mediated immunity vital to control growth Commonly infects dogs in endemic zones - severe or lethal |
|
Properties:
growth form |
Filamentous hyphae with aerial spores
Colonies appear cottony Produced in lab cultures at room temp Grows as yeast at 37C, smooth colonies Single buds and broad base |
|
Pathogenesis:
|
inhalation of spores from hyphae in soil -> Bad1 (blastomyces adhesin 1) promotes uptake by macrophages -> at 37C spores turn into yeast -> multiply in lung -> acute influenza-like pulmonary infection (may resolve or progress) -> yeasts disseminate via blood and lymph to visceral organs -> macrophages may carry yeast to other organs -> replicate in macrophages until they are activated by cytokines from T cells -> over several weeks, host develops acquired cell immunity (DTH appearance, T cell proliferation, circulating Abs) -> Cell med immunity leads to protection from infection
|
|
Environmental distribution:
Risk factors: Diagnosis: |
hard to ID because cross reactive DTH test with H. capsulatum - may be mississippi and ohio river basins and the carolinas
Recreationala activity in wooded areas grows only in yeast form in host, detect with KOH mount or fungal stains of tissue Also, immunodiffusion test for paitent Abs to A Ag produced from culture filtrates |
|
Coccidioides immitis
aka: Clinical significance: |
Valley fever
40% infections - lower resp infection and/or systemic illness symptoms, lasts 2-6 weeks Small # cases progress to chronic pulmonary form (*cavity formation) Disseminated disease - more common in immunosuppressed |
|
Structure (envt and host):
|
Envt - mycelial phase - barrel shaped arthroconidia, (arthospores hazardous to lab workers) easily fragmented, highly infectious, hazardous when cultured in lab
Host - large, thick walled spherules with numerous endospores |
|
Pathogenesis:
|
Inhaled arthroconidia -> lodge in alveoli -> develop to spherules in tissues -> spherule rupture -> release endospores into tissue -> endospores develop into spherules
Host response: Initially macroph and PMNs (fungi resist killing by PMNs) -> onset of CMI leads to protection from infection |
|
Epidemiology:
Where? Who? |
Where?
Fungus has been isolated from soil endemic to certain areas of N, S, and C America (e.g. central texas) Fungus grows in "Lower Sonoran Life Zone" - arid, hot, low altitude, alkaline soil, sparse flora Almost all of 100,000 annual infections are in SW US Who? common in men of dark skin and especially Filipino |
|
Diagnosis:
|
ID spherules with KOH mount or fungal stain of infected tissue
Culture organism on special media - demonstrate dimorphism and tissue form Skin test positive 1-4 wks post onset of primary symptoms (remains + for life) *dissem infect can cause anergy Serologic tests - monitor disease progress -IgM precipitating Ab positive within first three weeks - IgG complement fixing Abs develop later (titers increase as disease disseminates) - Abs disappear with disease resolution, persist with continued infection |
|
Prevention:
Treatment: |
avoid env't exposure
Antifungal therapy for disseminated |
|
Paracoccidioides brasiliensis:
|
wagon wheel appearance of yeasts found in tissues (due to circular budding)
|