ABSTRACT
The major endemic mycoses are defined by their heightened prevalence in specific geographic regions. In the Americas, Histoplasma capsulatum is concentrated in the Midwestern United States, most densely within the Ohio and Mississippi River basins, and south through Mexico, Central America, into South America, particularly Colombia, Venezuela, Brazil, and Argentina. Finally, a positive Histoplasmin skin test may stimulate the increase of anti-Histoplasma antibodies to titers >1:8, level suggesting active histoplasmosis. Given the interaction of the skin test and serologic titers of antibody, cross-reactivity with other endemic mycoses, and insensitivity among the immune suppressed, the use of the Histoplasmin skin test has been primarily to define areas of endemicity, and to explore populations exposed in epidemics. With a low intensity inoculum, histoplasmosis is often clinically silent in the immunocompetent patient. In the patient exposed to a very heavy inoculum, or with severe immunosuppression, the disease may progress directly to dissemination with diffuse pulmonary, lymphatic, splenic, hepatic, and bone marrow involvement.
