fungal pathogens Flashcards
where are histo, blasto and coccidioides found?
histo: further south, along mississippi and ohio river.
blasto: great lakes, mississippi river, ohio river. in wisconsin.
cocci: desert southewst
features all 3 have in common?
undergo “phenotype switching” and are dimorphic. all three fungi exist as free-living molds. diagnosis requires microscopic examination.
which convert to a budding yeast? what is other?
histo, blasto. Cocci converts to a large endosporulating spherule containing many endospores.
where does infection most commonly occur?
most often via the respiratory route: inhalation of infectious particles small enough (2-5 micrometers) to reach small airways and alveoli. Once in respiratory tract, the fungus converts to the pathogenic, host form. primary site of infection is the lung. The fungus may remain localized there causing pneumonia, or it may disseminate via the blood to other sites.
how can people infected with any of the three present?
cutaneous lesions. These lesions can be primary sites of infection. However, some cutaneous lesions and other
dermatologic manifestations can be a consequence of dissemination
histo ecology/environments?
acidic soil, esp with birds around.
prevalence of histo?
Endemic infection: in some geographical regions, incidence of histoplasmin (Histo culture
supernatant extract) skin-test immunological reactivity (indicating prior infection) exceeds 85%. Nearly all lifelong residents of endemic areas are exposed by 20 years of age.
histo morphology in environment?
multinucleated branched hyphae, with microconidia and macroconidia
histo morphology in host?
oval budding yeast (2-4 micrometers),
with NARROW bud neck; found inside mononuclear phagocytes, and extracellularly
process of primary histo infection?
main infectious form = microconidia because of their small size, ability to become airborne, penetrate into the deep lung and deposit in the alveoli. Microconidia are engulfed by
macrophages, wherein microconidia convert to the yeast form and begin replication
most frequent result of histo infection?
The most frequent result of infection (75-90% of the time) in immunocompetent people is an
asymptomatic infection or a non-specific flu-like syndrome (fever, chest pain, dry/non-productive
cough, headache, joint/muscle pain), which resolves. If symptoms occur, they start 3-17 d (ave 10 d) after exposure. In the general population, clinically severe disease is relatively
rare (<5%)
histo pulmonary clinical syndrome?
includes focal, nodular, diffuse and cavitary disease especially in emphysema
patients – can resemble miliary TB on X-ray, multiple calcified lesions in chronic or disseminated dz.
histo allergic/inflammatory sequellae?
fibrosing mediastinitis - an excessive fibrotic response to a prior episode of histoplasmosis. results from the enlargement of multiple lymph nodes that undergo necrosis and the subsequent leakage of antigen from caseous nodes into the mediastinum. This, in turn, stimulates an abnormal immunologic response leading ultimately to fibrosis. can have obstruction of SVR, cor pulmonale, mitral stenosis.
histo treatment?
Not all clinical manifestations require drug treatment. Called upon in severe or progressive disease, anti-fungal drugs are considered a therapeutic adjunct
blasto differences from other 2?
Blastomycosis is one endemic fungal infection for which there is NOT a clear association with
HIV/AIDS
