Blastomycosis

How blastomycosis is caught

Blastomyces grows as a mold in damp soil rich in decaying leaves and wood, often near lakes, rivers and beaver dams. When soil is disturbed, for example by digging, hunting, camping, fishing, logging, construction or clearing woodland, the spores become airborne. In the lungs, body temperature turns the mold into a yeast form that causes infection.

It does not spread from person to person. Dogs also get blastomycosis and can act as a warning that the fungus is present in an area, but people do not catch it from dogs.

Symptoms usually begin 3 weeks to 3 months after exposure.

Symptoms

Lung infection (most common)

• Cough, sometimes with mucus or blood
• Fever, chills and night sweats
• Chest pain
• Breathlessness
• Tiredness, muscle aches and weight loss

It often looks like ordinary pneumonia, bronchitis or flu, and is frequently diagnosed only after antibiotics fail. Chronic cases can mimic tuberculosis or lung cancer, with weight loss and a mass on X-ray. A small number of people develop severe pneumonia and acute respiratory distress syndrome.

Spread beyond the lungs

In about 25 to 40% of symptomatic cases, the infection spreads through the blood:

• Skin: the most common site. Raised, crusted, warty sores or ulcers with irregular borders, often on the face and limbs.
• Bones: bone infection (osteomyelitis), often in the spine, ribs and long bones, causing pain and swelling.
• Genitourinary system: prostate and epididymis in men.
• Brain and spinal cord: rare, mostly in people with weak immune systems.

Risk factors

• Living in or visiting endemic areas
• Outdoor work or recreation near waterways and wooded areas
• Weakened immune system (HIV, organ transplant, immune-suppressing medicines), which raises the risk of severe and spread disease

Diagnosis

Because symptoms are nonspecific, doctors need to think of it, especially when "pneumonia" does not respond to antibiotics in someone from an endemic area. Tests include:

• Microscopy and culture of sputum, bronchoscopy fluid, skin scrapings or biopsy tissue, which show the characteristic thick-walled yeast with broad-based budding
• Urine or blood antigen test, which can cross-react with histoplasmosis
• Antibody blood tests, which are less reliable
• Chest X-ray or CT: consolidation, masses or nodules
• Biopsy of skin or other lesions
• Imaging of bones or brain if symptoms suggest spread

Treatment

Most people with symptoms are treated, because untreated disease can progress or spread.

Itraconazole levels in the blood are checked to make sure enough is absorbed. It interacts with many medicines and can affect the liver, so monitoring is needed. Itraconazole is avoided in pregnancy, where amphotericin B is used instead.

Outlook

With treatment, most people recover fully, and relapse is uncommon if the full course is completed. Severe lung disease and infection in people with weak immune systems carry a higher risk of death, so early diagnosis matters.

Prevention

There is no vaccine, and avoiding soil exposure entirely is not practical in endemic regions. People with weakened immune systems may reduce their risk by avoiding activities that disturb soil and rotting wood in those areas.

Frequently asked questions

What is blastomycosis?

Blastomycosis is a fungal infection caused by inhaling spores of Blastomyces from soil and decaying wood. It mainly affects the lungs but can spread to the skin, bones and other organs. It is most common in parts of the central and eastern US and Canada.

What are the symptoms of blastomycosis?

Symptoms include cough, fever, chills, night sweats, chest pain, tiredness and weight loss, similar to pneumonia or flu. Spread to the skin causes crusted or warty sores. Many infected people have no symptoms at all.

Is blastomycosis contagious?

No. It does not spread between people or from animals to people. Both people and dogs catch it from the same environmental source, so a sick dog can signal that the fungus is present locally.

How is blastomycosis treated?

Mild to moderate cases are treated with itraconazole tablets for 6 to 12 months. Severe cases start with IV amphotericin B in hospital, followed by itraconazole. Treatment is longer for bone or brain infection.

Can blastomycosis be cured?

Yes. Most people are cured with a full course of antifungal treatment. Completing the course is important, because stopping early increases the chance of the infection coming back.