Mycology, pathogenesis, and epidemiology of blastomycosis
- Robert W Bradsher, Jr, MD
Robert W Bradsher, Jr, MD
- Professor of Medicine
- University of Arkansas for Medical Sciences
Blastomycosis is a systemic pyogranulomatous infection, primarily involving the lungs, that arises after inhalation of the conidia of Blastomyces dermatitidis. Blastomycosis of the lung can be an asymptomatic infection or can manifest as acute or chronic pneumonia. Hematogenous dissemination frequently occurs; extrapulmonary disease of the skin, bones, and genitourinary system is common, but almost any organ can be infected.
The basic mycology, pathogenesis, and epidemiology of blastomycosis will be reviewed here. The clinical manifestations and treatment of blastomycosis are discussed separately. (See "Clinical manifestations and diagnosis of blastomycosis" and "Treatment of blastomycosis".)
Blastomyces dermatitidis is the asexual state of Ajellomyces dermatitidis. A. dermatitidis is the sexual stage of the organism. Production of a sexual spore requires fusion of the nucleus of a positive type with a negative, the so-called heterothallic property; both mating types are equally capable of causing infection .
Two serotypes of B. dermatitidis have been identified based upon the presence or absence of the A antigen. In a study of 102 isolates predominantly from North America, all of the North American isolates reacted with anti-A antibody, while 11 of 12 isolates from Africa failed to react . Serologic differences in B. dermatitidis isolates from different geographic location in the United States and Africa have been detected using an enzyme-linked immunoassay, indicating that different genotypic groups exist [3-5].
Phylogenetic analysis of 78 clinical and environmental isolates of B. dermatitidis from different geographic regions has revealed two distinct species of the fungus, B. dermatitidis and B. gilchristii . B. gilchristii was isolated from two North American locations known to be hyperendemic for blastomycosis, the Kenora region of Ontario and the Eagle River region of Wisconsin. The authors speculated about whether the high rates of infection in these areas might be due to B. gilchristii being a more pathogenic species or whether favorable environmental factors allowed emergence of this species. Additional studies are needed using isolates from other sites to establish the prevalence of B. gilchristii.
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