Blastomycosis.

Blastomycosis is a serious fungal disease of humans and other mammals caused by environmentally acquired infection with geographically restricted, thermally dimorphic fungi belonging to the genus . The genetic and geographic diversity of these pathogens is greater than previously appreciated. In addition to and the cryptic species , which cause blastomycosis in mid-western and various eastern areas of North America, atypical blastomycosis is occasionally caused by in western parts of North America and in Africa. Blastomycosis is acquired by inhalation of the conidia that are produced in the mold phase; in the lungs, temperature-dependent transformation occurs to the yeast phase. In this form, the organism is phagocytized by macrophages and can spread hematogenously to various organs causing disseminated infection. Pulmonary disease is most common and varies from mild, self-limited infection to severe, potentially fatal adult respiratory distress syndrome. Disseminated infection is manifested primarily by skin lesions, but many other organs can be involved. Diagnosis is established by growth of the organism in culture; however, a tentative diagnosis can be made quickly by histopathological identification of the classic yeast form in tissues or by finding antigen in urine or serum. Blastomycosis is treated initially with amphotericin B when the disease is severe, involves the central nervous system, or the host is immunosuppressed. Itraconazole is recommended for primary therapy in mild-to-moderate infection and for step-down therapy after initial amphotericin B treatment. Voriconazole and posaconazole can be used for patients in whom itraconazole is not tolerated.