Blastomycosis is a fungal disease caused by Blastomyces dermatitidis.
This fungus most commonly infects humans and animals through the respiratory tract. After spores are inhaled, they settle in the small airways and begin to reproduce. Subsequent to this, the organism spreads throughout the body to involve many organs. Infrequently, infection occurs through inoculation of an open wound. Although researchers in human medicine have been mostly unsuccessful in reliably isolating the organism from the environment, it does appear that both humans and animals become infected from particular environmental sources, probably the soil.