Blastomycosis is a rare fungal infection. It is caused by inhaling a fungus called Blasomyces dermatitidis, which is found in wood and soil. It is also known as Chicago disease or Gilchrist’s disease. It occurs most often in people living in the south-central and Midwestern regions of the United States and Canada, especially along the Mississippi and Ohio Rivers, around the Great Lakes, and in and around Ontario, but has also been reported in locations all over the world. It afflicts men more often than women, usually between the ages of 20 and 40. Outbreaks have been associated with activities around streams or rivers with high content of moist soil enriched with organic debris or rotting wood. The fungus is breathed in from its natural habitat, where it incubates in the lungs over a period of 30 to 100 days, and spreads to other parts of the body. It is especially harmful to those who have weakened immune systems, such as those with HIV, organ transplants, or other medical treatments that lower the immune system. It is also common in dogs, and can be found less commonly in cats.
