Fungi II - Primary pathogenic fungi

Primary pathogenic fungi are dimorphic. At 37C they grow as yeast. They are very similar to TB. Like TB, they require cell-mediated immunity to clear (Type IV) -- they even have equivalent antigen skin tests, like PPD for TB.

Coccidiodes immitis

Forms alternating arthroconidia in mycelia; these are infectious when inhaled. In tissue grow as large spherules filled with endospores within caseating granulomas. Endemic to Southwestern United States and Northern Mexico. San Joaquin Valley fever. Anything that disturbs soil (earthquakes) can cause increase in cases. Disseminated disease only in 5% of infections, more likely in immunocompromised: skin granulomas, lytic bone granulomas, meningitis (the worst). High titer of antibody associated with poor prognosis -- indicates disseminated disease. Black or Filipino population at higher risk for disseminated disease. Diagnosis: culture, antibody test, skin test.

Histoplasma capsulatum

Associated with bird and bat droppings (at risk if cleaning chicken cage, spelunking). Endemic to Mississippi and Ohio River valleys. Not that pathogenic: often asymptomatic, or mild pneumonia. Microconidia or tuberculate macroconidia (pathognomonic). Doesn't have true capsule; called capsulatum because of histological apperance -- clear space around the yeast. Hide out in macrophages as intracellular parasites. Small, so can see many inside one macrophage. Disseminated disease in immunocompromised, may be mistaken for cancer due to wasting, possibly associated with TNF inhibitors. Antibody level is not a useful prognostic sign; antigen test, skin test, and culture used for diagnosis.

Blastomyces dermatitidis
Hardest to get (rarest, get it from rotten wood and soil) and hardest to have (often disseminated, even in non-immunocompromised). Endemic to states east of Mississippi and Central America. Inflammatory lung disease, and commonly disseminates to skin and bone where it forms granulomatous nodules. Broad-based bud (as opposed to Histoplasma, with narrow neck). No antibody test. Culture for diagnosis.

Sporothrix schenckii

Also known as rose gardener's disease. Inoculated by trauma to skin (rose thorn for instance). Local pustule or ulcer, with ascending lymphangitis. Dimoprhic fungus, cigar-shaped yeast at 37C.