In the United States, histoplasmosis is endemic in the Mississippi-Missouri-Ohio River Valley where a warm, moist environment provides optimal conditions for the growth of Histoplasma capsulatum in a favorable soil. Infection is not limited to this geographic area, however, and in both endemic and nonendemic areas, microenvironments of both high and low incidence of infection exist. These microenvironments are related to local recovery rates of the fungus from the soil; high rates have been particularly associated with areas where birds or bats or both congregate, roost, and hibernate.1,2 While naturally infected birds are not known to exist, their droppings and feathers apparently provide nutrients which facilitate growth in an appropriate soil under favorable environmental conditions.3 Bat droppings provide similar nutrients but, in addition, may contain the fungus and could conceivably serve as a source for direct transmission to man or provide a method of dissemination of spores from
Fass RJ, Saslaw S. Earth Day Histoplasmosis: A New Type of Urban Pollution. Arch Intern Med. 1971;128(4):588–590. doi:10.1001/archinte.1971.00310220096013
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