In these areas, there are about 1 to 2 cases per 100,000 per year. Less frequently, blastomycosis also occurs in Africa, the Middle East, India, and western North America. Blastomycosis also affects a broad range of non-human mammals, and dogs in particular are an order of magnitude more likely to contract the disease than humans. The ecological niche of Blastomyces in the wild is poorly understood, and it is unknown if there are any significant host animals.Blastomycosis has existed for millions of years but was first described by Thomas Caspar Gilchrist in 1894. Because of this, it is sometimes called "Gilchrists disease". Signs and symptoms
The symptoms of blastomycosis cover a wide range, overlapping with more common conditions; for this reason, blastomycosis has often been called "the great pretender". Many cases are asymptomatic or subclinical. Lung symptoms are common, because the lungs are infected in 79% of blastomycosis cases. However, in 25-40% of cases the disease also disseminates to other organs, including the skin.The extent and severity of symptoms depends in part on a persons immune status; less than 50% of healthy people with blastomycosis have symptoms, while immunocompromised patients are especially likely to have the disease spread beyond the lungs to other organs like the skin and bones.Blastomycosis manifests as a primary lung infection in about 79% of cases. The onset is relatively slow and symptoms are suggestive of bacterial pneumonia, often leading to initial treatment with antibacterials.
Other recurring sites of dissemination are the genitourinary tract (kidney, prostate, epididymis; collectively ca. 25% of cases) and the brain (3–10% of cases). 40% of immunocompromised individuals have CNS involvement and present as brain abscess, epidural abscess or meningitis. Blastomycosis in non-lung organs such as the skin may present a very wide range of symptoms, including the following:

skin lesions, which may be verrucous (wart-like) or ulcerated with small pustules at the margins. bone or joint pain due to bone lytic lesions. pain when urinating due to prostatitis. hoarseness due to laryngeal involvement. headache, confusion or other neurological symptoms caused by central nervous system involvement. Cause
Blastomycosis is caused by dimorphic fungi in the genus Blastomyces, in the phylum Ascomycota and family Ajellomycetaceae. In eastern North America, the most common cause of blastomycosis is Blastomyces dermatitidis, but Blastomyces gilchristii has been associated with some outbreaks. In western North America, many cases of blastomycosis are caused by Blastomyces helicus, which most commonly attacks immunodeficient people and domestic animals. The species Blastomyces percursus causes many cases of blastomycosis in Africa and the Middle East. In Africa, blastomycosis may also be caused by Blastomyces emzantsi, which is often associated with infections outside the lungs.In endemic areas, Blastomyces dermatitidis lives in soil and rotten wood near lakes and rivers. Although it has never been directly observed growing in nature, it is thought to grow there as a cottony white mold, similar to the growth seen in artificial culture at 25 °C. The moist, acidic soil in the surrounding woodland harbors the fungus.