Blastomyces

Blastomyces is a genus of thermally dimorphic fungi in the family Ajellomycetaceae. The most clinically significant species are Blastomyces dermatitidis, Blastomyces gilchristii, and Blastomyces percursus, which cause blastomycosis in humans. In the environment the organism grows as a mold producing conidia, while at human body temperature it converts to a yeast form with broad-based budding.

Geography and ecology: Blastomyces is endemic in parts of North America, especially around the Mississippi and Ohio river valleys and the Great Lakes region, with reports in southern Canada. The natural reservoir is soil and decaying organic matter, often near waterways.

Transmission and disease: Infection begins by inhalation of fungal propagules from the environment. After deposition in the lungs, disease may remain localized or disseminate hematogenously to skin, bone, and, less frequently, the genitourinary tract or central nervous system. The incubation period is typically several weeks to a few months. Pulmonary disease is the most common presentation; disseminated infection commonly involves cutaneous lesions that appear as verrucous or ulcerated nodules, and bone or CNS involvement can occur.

Diagnosis and treatment: Diagnosis relies on culture or tissue histology showing broad-based budding yeast, supplemented by antigen testing in urine or serum. Imaging often shows focal consolidation or nodules. Mild to moderate disease is usually treated with itraconazole for at least 6–12 months; severe or disseminated disease, or CNS involvement, requires amphotericin B induction followed by an azole. Duration depends on site and response.

Prevention and prognosis: There is no vaccine. Avoiding heavy exposure to soil in endemic areas is advised; prognosis improves with early diagnosis and treatment but disseminated disease can be fatal without therapy.