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".)
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. There is speculation as to 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.
The natural habitat of 169 strains of organisms collected from various geographic areas were examined with 25 microsatellite loci for phylogeographic analysis . B. gilchristii strains were found only in isolates from Canada and some northern states in the US, while B. dermatitidis were from those same locations, plus along the Mississippi River drainage system and in southeastern states. Both were closely linked to freshwater drainage systems, and the diversity was speculated to have begun with receding glaciers covering much of North America in the Pleistocene epoch .
Clinically, the organisms appear to cause similar clinical illness and will be referred to as B. dermatitidis hereafter. B. dermatitidis refers to both the sexual and asexual stage of the organism. Previously, Ajellomyces dermatitidis was the name of the sexual stage of the organism, and B. dermatitidis was the name for the asexual state 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 .
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