Blastomycosis is an infection, caused by a fungus, that can be severe. It most often will affect the lungs and the skin. In the United States, this fungus can be found in wooded areas of the Midwest, South Central and Southeast. An infected person may be symptom free, have mild flu-like symptoms, or develop an illness that progresses to involve multiple body symptoms in an untreated individual. People and animals are not known to spread the infection.