Blastomycosis

Blastomycosis is a fungal infection of humans and other mammals caused by the genus Blastomyces, an environmentally restricted and geographically confined thermally dimorphic fungus. These pathogens show greater genetic and geographic diversity. Blastomyces species of importance include Blastomyces dermatitidis, the cryptic species Blastomyces gilchristii (various eastern areas of North America and midwestern region), and Blastomyces helicus (western parts of North America). Blastomyces percusus and Blastomyces emzantsi are infrequent causes of blastomycosis in the Middle East and Africa. Blastomyces parvus has also been identified as a sporadic agent of atypical, granulomatous pulmonary blastomycosis. Blastomycosis is acquired by inhaling conidia produced during the mycelium stage. Temperature-dependent conversion to the pathogenic yeast phase takes place in the lung. Clinical manifestations are protean. They vary from asymptomatic infection to symptomatic manifestations ranging from acute pneumonia to severe respiratory distress. Lung involvement is most frequent and varies in severity from mild infections to fatal respiratory distress syndrome in adults. Diagnosis is based on histopathology, detection of typical broad-based budding yeast form in tissues, or detection of antigen in urine or serum. Culture remains the gold standard for diagnosis. Blastomycosis in patients with severe disease, central nervous system involvement, or immunocompromised hosts is treated with induction therapy by amphotericin B. Itraconazole is the first-line treatment for mild to moderate infections and for maintenance therapy after initial induction with amphotericin B. In conditions where itraconazole is contraindicated, posaconazole or voriconazole is used.