Blastomycosis

• Blastomycosis is a fungal infection.
• Blastomycosis is caused by a dimorphic (has two forms) fungus termed Blastomyces dermatitidis.
• Risk factors include immunocompromised patients, and traveling or living in densely wooded areas.
• Symptoms resemble the flu (fever, chills, cough, and discomfort or pain in the muscles, joints, and chest) but may become more severe and prolonged; skin lesions may develop and other organ systems may be affected.
• Seek medical care if you develop symptoms and have risk factors.
• Blastomycosis is diagnosed by culturing the fungi from infected organ systems (biopsy samples).
• Blastomycosis should be treated by medical caregivers, not by self-care at home.
• Medical treatment is done with long-term (six to 12 months) antifungal drugs.
• Blastomycosis follow-up is very important to obtain the proper treatment and to check for reinfection by the fungus.
• Blastomycosis prognosis is variable; most patients do well, but immunocompromised patients have a prognosis that can vary from good to poor.
• Currently, there is no vaccine available to protect against blastomycosis; avoidance of wooded areas where the fungi thrive is advised by the CDC.

Blastomycosis is an infection caused by various related genotypes of the fungus Blastomyces dermatitidis. Blastomycosis is also termed North American blastomycosis, Gilchrist's disease, and blastomycetic dermatitis. Blastomycosis is found predominately in the central and southeast U.S., although it does occur in Canada, Africa, and sporadically in a few other countries. The fungi can infect many types of animals (for example, dogs, cats, bats, lions, horses) and humans. The vast majority of infections occur in the lungs.

Blastomycosis is caused when the conidial forms (spores) of the fungus become airborne and are inhaled by a person or susceptible animal. Although the spores can be destroyed by specialized lung cells, the fungal cells are dimorphic and some spores may change into a yeast-like form that is much more resistant to the lung's defensive cells. The body temperature triggers the change from spores to yeast forms; these yeast forms multiply, and some may be transferred to other organs and the skin by the blood or lymphatic system. This action happens during the incubation period described below in the symptom section.

Picture of yeast-like cells of Blastomyces dermatitidis from a patient with blastomycosis; SOURCE: CDC/Dr. William Kaplan

Although almost anyone can become infected with the fungi, those at highest risk for blastomycosis are immunosuppressed individuals and those that live in or visit areas where the fungal spores are plentiful. Since the fungi prefer damp forested areas, people who are hunters, forestry workers, campers, and farmers are at higher risk to get blastomycosis. Blastomycosis cannot be spread from person to person or animal to person.

Fortunately, about 50% of all people infected with the fungi do not show any symptoms of blastomycosis. When symptoms of blastomycosis do occur, they appear after a latent or incubation period of time that ranges from about three to 15 weeks after the initial exposure to the fungi. Unfortunately, the initial symptoms of blastomycosis resemble flu symptoms (fever, chills, cough, and discomfort or pain in the muscles, joints, and chest). If blastomycosis is spread by the blood or lymphatic system, skin lesions or bone lesions may develop.

Picture of skin lesions due to blastomycosis; SOURCE: CDC

People should seek medical care if they are or have been at risk for coming in contact with the fungi and are immunosuppressed from any cause. Others should seek care if they have the same exposure risk as above and develop flu-like symptoms, especially during the periods of low flu activity (usually late spring through early fall) or they develop prolonged symptoms (usually greater than two weeks) that may increase in severity and/or develop skin nodules.

The presumptive diagnosis of blastomycosis is done by obtaining the patient's history and by seeing the fungi in samples taken from skin scrapings or other infected tissue and examined microscopically. However, the definitive diagnosis of blastomycosis is done by isolating (growing) the fungus from one or more tissue samples (blood, sputum samples or biopsy samples from skin, bone marrow, liver, or other organs). In addition, there are immunology-based tests that can detect fungi present in urine or blood. Another available test can detect antibodies directed against the fungi; this test indicates whether the person has been exposed to the fungi but does not determine active infection.

Blastomycosis should not be attempted at home; a physician needs to diagnose, treat, and follow up with the infected patient to be sure the patient has adequate treatments and does not relapse.

The most commonly used treatment for blastomycosis is an antifungal drug termed itraconazole (Sporanox). It may be used alone to treat mild to moderate blastomycosis infections. Patients with more severe disease may be treated with amphotericin B. Some severely ill patients are treated with both amphotericin B and itraconazole. There are other drugs related to itraconazole (the azole family of antibiotics), but none are as effective as itraconazole. In general, most clinicians treat the patient for about six to 12 months. Some immunosuppressed patients may require lifelong suppressive therapy with itraconazole. Newer antifungal drugs are being evaluated to treat blastomycosis.

Follow-up is important for patients with blastomycosis because the treatment should be regularly given over long terms of time (often six to 12 months). Itraconazole blood levels should be examined to be sure the dosage is effective, and patients need to be monitored for symptom resolution or relapses by the doctor.

The prognoses (outcomes) for blastomycosis is variable; about 50% of infections do not even produce symptoms. Those patients diagnosed and treated appropriately usually have a good outcome although they need to take medications for many months. Immunosuppressed patients with blastomycosis have outcomes that range from good to poor. Although some may recover completely, the mortality rate (death rate) is about 29%. It can be as high as 40% with patients with AIDS, and 68% with ARDS.

Prevention of blastomycosis is difficult because the fungi are widespread in the U.S. and many other countries. The CDC recommends that immunocompromised people avoid going into thickly wooded areas where the fungi occur in high numbers. Currently, there are no vaccines available to protect individuals from the fungi that cause blastomycosis, but researchers are trying to develop a vaccine.