Blastomycosis is a rare infection that may develop when people inhale a fungus called Blastomyces dermatitidis, a fungus that is found in moist soil, particularly where there is rotting vegetation. The fungus enters the body through the lungs, infecting them. The fungus then spreads to other areas of the body.The infection may affect the skin, bones and joints, and other areas. The disease usually affects people with weakened immune systems, such as those with HIV or who have had an organ transplant.