| Summary: | Blastomycosis is caused by a thermally dimorphic fungus that thrives in moist acidic soil. <i>Blastomyces dermatitidis</i> is the species responsible for most infections in North America and is especially common in areas around the Great Lakes, the St. Lawrence Seaway, and in several south-central and southeastern United States. Other <i>Blastomyces</i> species have more recently been discovered to cause disease in distinct geographic regions around the world. Infection almost always occurs following inhalation of conidia produced in the mold phase. Acute pulmonary infection ranges from asymptomatic to typical community-acquired pneumonia; more chronic forms of pulmonary infection can present as mass-like lesions or cavitary pneumonia. Infrequently, pulmonary infection can progress to acute respiratory distress syndrome that is associated with a high mortality rate. After initial pulmonary infection, hematogenous dissemination of the yeast form of <i>Blastomyces</i> is common. Most often this is manifested by cutaneous lesions, but osteoarticular, genitourinary, and central nervous system (CNS) involvement also occurs. The diagnosis of blastomycosis can be made by growth of the mold phase of <i>Blastomyces</i> spp. in culture or by histopathological identification of the distinctive features of the yeast form in tissues. Detection of cell wall antigens of <i>Blastomyces</i> in urine or serum provides a rapid method for a probable diagnosis of blastomycosis, but cross-reactivity with other endemic mycoses commonly occurs. Treatment of severe pulmonary or disseminated blastomycosis and CNS blastomycosis initially is with a lipid formulation of amphotericin B. After improvement, therapy can be changed to an oral azole, almost always itraconazole. With mild to moderate pulmonary or disseminated blastomycosis, oral itraconazole treatment is recommended.
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