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Blastomycosis is an invasive fungal infection caused by the spores of the dimorphic fungi belonging to the genus Blastomyces, most commonly Blastomyces dermatitidis and occasionally Blastomyces gilchristii, Blastomyces helicus or Blastomyces percursus.

Epidemiology and distribution

Blastomyces dermatitidis is endemic in the soils of the Ohio and Mississippi River Valleys, Great Lakes region, and the southeastern United States. Early efforts to isolate Blastomyces from soil samples relied on culture or recovery from intravenous injection of soil samples into mice, which was a laborious and often unsuccessful process. Thanks to PCR technology, Blastomyces have been successfully identified in the expected ecologic niche (moist, acidic soil, particularly in wooded areas near rivers or other water sources) and tissues of animals exposed to these environments.
As a result, Blastomyces are frequently recorded in people who work outside, fish or hunt, or have recently been exposed to regions where soil and plants have been disturbed, for example, for excavation or construction. Moreover, in the endemic regions, the risk of blastomycosis is particularly high in dogs, especially hunting and sporting dogs. This high risk is likely due to their close proximity to the soil, together with sniffing and digging behaviour, reinforcing the soil-spore link.