Blastomyces dermatitidis is a thermally dimorphic fungus and a probable saprobe of the soil. It specifically inhabits decaying wood material. Blastomyces dermatitidis is very rarely isolated as a natural habitat. Isolation from the environment is most likely when the sample contains soil and is rich in organic material such as animal feces, plant fragments, insect remains, and dust. If the substrate is moist, lacks exposure to direct sunlight, contains organic debris, and has a pH of less than 6.0, isolation of Blastomyces dermatitidis is probable. It is endemic in North America. Mississippi, Ohio and Missouri valleys are the geographic locations with highest incidence of infections due to Blastomyces dermatitidis. African type Blastomyces dermatitidis strains isolated from cases in Africa also exist. It was demonstrated that African type strains are not identical with the North American strains. These two groups most probably constitute two distinct serotypes of Blastomyces dermatitidis showing geographic diversity. They have common and varying antigens
