Blastomycosis is an infection caused by the fungus Blastomyces dermatitidis, a microscopic organism found in specific environmental settings. This fungus primarily affects the lungs but can spread to other parts of the body. Understanding where this fungus lives and how it causes infection can help individuals in endemic areas recognize and mitigate risks.
Understanding the Fungus and Its Environment
Blastomyces dermatitidis is a dimorphic fungus, meaning it can exist in two different forms depending on the temperature. In the natural environment, it grows as a fluffy white mold at around 25 degrees Celsius (77 degrees Fahrenheit). Once it enters a warm-blooded host, like a human, it transforms into a brown, folded yeast form at body temperature, around 37 degrees Celsius (98.6 degrees Fahrenheit).
This fungus thrives in moist, acidic soil, often in areas rich with decaying organic matter such as wood and leaves. It is commonly found near waterways like rivers, lakes, and streams. In North America, Blastomyces dermatitidis is endemic to the Midwestern, South Central, and Southeastern United States, particularly around the Ohio and Mississippi River valleys and the Great Lakes region. It is also prevalent in parts of Canada, including Ontario, Manitoba, and Quebec.
How Infection Occurs
Infection with Blastomyces dermatitidis occurs through the inhalation of airborne fungal spores, known as conidia. These tiny spores are released into the air when contaminated soil or decaying wood is disturbed, such as during construction, excavation, or outdoor activities like hunting, camping, or farming. Once inhaled, the conidia travel into the lungs.
Inside the lungs, the spores encounter the warmer body temperature and transform into the yeast form. This yeast form can then multiply and cause an infection. Blastomycosis is not typically contagious and does not spread from person to person, or from animals to people.
Recognizing the Signs of Blastomycosis
The symptoms of blastomycosis can vary widely, ranging from no symptoms to severe, life-threatening illness. Approximately half of individuals infected with Blastomyces do not develop symptoms. When symptoms do occur, they appear between three weeks and three months after exposure.
The most common form of the disease is pulmonary blastomycosis, which affects the lungs and can resemble other respiratory illnesses. Symptoms may include fever, cough that can be dry or produce pus or blood, chest pain, shortness of breath, fatigue, and muscle aches. Some individuals might also experience chills, night sweats, and weight loss.
The infection can spread beyond the lungs, leading to disseminated blastomycosis. The skin is a common site for dissemination, presenting as lesions, ulcers, or nodules that can be crusted or wart-like. The infection can also affect bones and joints, causing pain and swelling. Central nervous system involvement can occur, leading to headaches or seizures.
Diagnosing and Treating the Infection
Diagnosing blastomycosis requires clinical suspicion due to its varied presentation. Healthcare providers may examine tissue or fluid samples, such as sputum or samples from skin lesions, under a microscope to look for characteristic yeast cells. Fungal cultures can take several days to weeks to yield results.
Urine antigen tests can help detect fungal components, offering a faster diagnostic option. Serology, which involves blood tests for antibodies, can also be used. Once diagnosed, blastomycosis is treated with antifungal medications.
For mild to moderate cases, oral azole antifungals, such as itraconazole, are typically prescribed for several months. For severe or life-threatening infections, or cases involving the central nervous system, an intravenous medication called amphotericin B may be used initially, sometimes followed by itraconazole. Treatment is usually long-term, often lasting 6 to 12 months, to ensure the infection is fully cleared and to prevent recurrence.
Reducing Your Risk
Certain individuals face a higher likelihood of exposure or developing severe blastomycosis. This includes people with weakened immune systems, such as those with HIV/AIDS or organ transplants. Individuals who engage in outdoor activities that disturb soil in endemic areas, like forestry workers, hunters, campers, or construction workers, are also at increased risk.
Some practical steps can help reduce the risk. Avoiding activities that stir up large amounts of soil in known endemic regions is recommended. When working in high-risk environments, wearing protective gear like N-95 masks can help minimize the inhalation of fungal spores. Being aware of symptoms after potential exposure and seeking medical attention promptly is important for early diagnosis and treatment.