Blastomycosis is not known to spread from person to person. Only about half of the people who are infected will show symptoms. The symptoms of blastomycosis usually appear between 3 and 15 weeks after being exposed to the fungus and are similar to flu symptoms, and include fever, chills, cough, muscle aches, joint pain, and chest pain. In very serious cases of blastomycosis, the fungus can disseminate, or spread to other parts of the body, such as the skin and bones.
The best way to diagnose the infection is to perform a fungal culture. Doctors take small samples from tissues or body fluids, such as blood, sputum, bone marrow, liver, or skin and see if the fungus will grow from these samples in a laboratory. Blastomycosis can also be diagnosed by looking at a small sample of infected tissue under a microscope. An antigen test can detect the presence of the fungus in a urine or serum sample, and a blood test can measure prior exposure to the fungus by detecting Blastomycosis antibodies.
Smear from a foot lesion showing a Blastomyces dermatitidis yeast cell.
There is no vaccine to prevent blastomycosis. In endemic regions, such as the Mississippi and Ohio River valleys, it may not be possible to completely avoid being exposed to the fungus. However, people who have weakened immune systems may consider avoiding wooded areas where the fungus is prevalent.