Epidemiology

Endemic mycoses are true primary fungal pathogens capable of causing infection in otherwise healthy individuals. In immunocompromised patients, endemic fungal infections often present with a more fulminant course (in the case of primary infections) or reactivate to cause life-threatening infection. Because initial symptoms of an endemic fungal infection are often nonspecific and overlap with other slowly-progressing infections (e.g., tuberculosis), a careful patient history concerning travel and activities associated with potential exposure to soil contaminated with endemic fungi is essential for the diagnosis and early treatment of infection.

Two of the most common endemic fungal infections (histoplasmosis and North

American blastomycosis) are found in overlapping regions in the eastern and central river basins of the United States (Fig. 84-1). Histoplasma capsulatum var. capsu-

latum, the causative fungus of histoplasmosis, grows heavily in soil contaminated

with bird or bat excreta, which serve to enhance sporulation of the fungus. Activities in endemic regions that are classically associated with high exposures to Histoplasma capsulatum include cave exploration (spelunking), working in or demolishing chicken coops, demolition of older buildings, woodcutting in forests with large bird roosts, or spreading avian excreta as fertilizer. For blastomycosis, decaying organic matter, warm humid conditions, and proximity to water or frequent rainfall seems to support growth of this fungus. Occupational or recreational activities that disturb soil heavily contaminated with Blastomyces dermatitidis are common risk factors for development of blastomycosis. Coccidioidomycosis differs from histoplasmosis and blasto-mycosis, as the fungus is associated with arid to semiarid climates, hot summers, low altitude, alkaline soil, and sparse flora. Hence the fungus is found in the southwestern regions of the United States stretching from western Texas to southern California (see Fig. 84-1).4 Epidemics of coccidioidomycosis have been reported in California following dust storms and earth quakes, including cycles ofintense drought and rain, which favor the growth cycle of the fungus and enhance dispersion of its specialized spore forms called arthroconidia.

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