Blastomyces dermatitidis is a dimorphic fungus that causes blastomycosis, an invasive and often serious fungal infection found occasionally in humans and other animals.
The fungus is endemic to parts of eastern North America, particularly boreal northern Ontario, southeastern Manitoba, Quebec south of the St. Lawrence River, parts of the U.S. Appalachian mountains and interconnected eastern mountain chains, the west bank of Lake Michigan, the state of Wisconsin, and the entire Mississippi Valley including the valleys of some major tributaries such as the Ohio River.
[1] Blastomycosis is generally readily treatable with systemic antifungal drugs once it is correctly diagnosed; however, delayed diagnosis is very common except in highly endemic areas.
Blastomyces dermatitidis is the causal agent of blastomycosis, a potentially very serious disease that typically begins with a characteristically subtle pneumonia-like infection that may progress, after 1–6 months, to a disseminated phase that causes lesions to form in capillary beds throughout the body, most notably the skin, internal organs, central nervous system and bone marrow.
Along with two other important human-pathogenic fungi, Histoplasma capsulatum, Paracoccidioides brasiliensis and Polytolypa hystricis, species of Blastomyces belong to the family Ajellomycetaceae.
The geographic range of B. dermatitidis is largely focused around the waterways of the St. Lawrence and Mississippi River systems of North America.
There is a widely distributed and much republished, partially erroneous map that shows the U.S. portion of this range accurately, inclusive of occurrence in Minnesota, Wisconsin, Ohio, Kentucky, Arkansas, Tennessee, North and South Carolina, the Virginias, Mississippi, Louisiana, and a few regions of states adjacent to those named.
More direct and economical mycological techniques for environmental isolation, such as dilution plating, have never yielded positive results for Blastomyces growth.
[16] Recently, in an important breakthrough, a specific PCR technique was developed that was able to detect B. dermatitidis in three environmental samples from a dog kennel that had been experiencing problems with blastomycosis.
[19] There has been a long history of justifiable speculation that B. dermatitidis may associate in nature with one or more indigenous North American mammalian host species.
Unsubstantiated suspicion has particularly focused on the beaver,[18][20][21] but the shrew,[22] the bat[23] and the prairie dog[24] have also been focal points of interest, with no conclusive interspecies association being demonstrated to date.
The closely related pathogenic fungus P. brasiliensis in South America has a well substantiated, though not well understood, ecological link with the nine-banded armadillo, Dasypus novemcinctus.