Infection with Histoplasma capsulatum occurs commonly in areas in the Midwestern United States and Central America, but symptomatic disease requiring medical care is manifest in very few patients. The extent of disease depends on the number of conidia inhaled and the function of the host's cellular immune system. Pulmonary
infection is the primary manifestation of
histoplasmosis, varying from mild
pneumonitis to severe
acute respiratory distress syndrome. In those with
emphysema, a chronic progressive form of
histoplasmosis can ensue. Dissemination of H. capsulatum within macrophages is common and becomes symptomatic primarily in patients with defects in cellular immunity. The spectrum of disseminated
infection includes acute, severe, life-threatening
sepsis and chronic, slowly progressive
infection. Diagnostic accuracy has improved greatly with the use of an assay for Histoplasma
antigen in the urine; serology remains useful for certain forms of
histoplasmosis, and culture is the ultimate confirming diagnostic test. Classically,
histoplasmosis has been treated with long courses of
amphotericin B. Today,
amphotericin B is rarely used except for severe
infection and then only for a few weeks, followed by
azole therapy.
Itraconazole is the
azole of choice following initial
amphotericin B treatment and for primary treatment of mild to moderate
histoplasmosis.