Etiologic agent = Histoplasma capsulatum

Geographic distribution: The geographic distribution of Histoplasma capsulatum largely follows the Ohio, Mississippi and Missouri River valleys.

Histoplasma capsulatum prefers moist soils of high nitrogen content, hence the association with areas of bat guano or bird droppings.

• There is a classic story of Boy Scouts who were infected while doing their good deed cleaning out starling roosts!
• Infection has also been documented in spelunkers.

Recent studies (see Klein, 2000; Sebghati et al., 2000) have enhanced our understanding of how Histoplasma persists in the host. This yeast lives in the phagosomes of macrophages and is able to block phagosome/lysosome fusion and phagosome acidification so as to survive this normally hostile environment.

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