In terms of weather, both unusually dry weather and unusually moist weather have been cited. The seemingly contradictory data can most likely be reconciled by proposing that B. dermatitidis prospers in its natural habitats in times of moisture and moderate warmth, but that inoculum formed during these periods remains alive for some time and can be released into the air by subsequent dust formation under dry conditions. Indeed, dust per se or construction potentially linked to dust has been associated with several outbreaks The data, then, tend to link blastomycosis to all weather, climate and atmospheric conditions except freezing weather, periods of snow cover, and extended periods of hot, dry summer weather in which soil is not agitated. Gender bias
Sex is another factor inconstantly linked to contraction of blastomycosis: though many studies show more men than women affected, some show no sex-related bias. As mentioned above, most cases are in middle aged adults, but all age groups are affected, and cases in children are not uncommon. Ethnic populations
Ethnic group or race is frequently investigated in epidemiological studies of blastomycosis, but is potentially confounded by differences in residence and in quality and accessibility of medical care, factors that have not been stringently controlled for to date. In the United States, some studies show a disproportionately high incidence and/or mortality rate for blastomycosis among Black people.In Canada, some studies, but not others, indicate that First Nations people have a disproportionately high incidence of blastomycosis. Incidence in First Nations children may be unusually high.
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.