Reporting Obligations

Individuals with suspect or confirmed cases must be reported to the Thunder Bay District Health Unit by the next working day by fax, phone or mail.

  • Fax: (807) 625-4822
  • Phone: 625-8318 or toll-free at 1-888-294—6630, ext. 8318
  • Mail: 999 Balmoral Street, Thunder Bay, ON P7B 6E7


Aetiologic Agent:

Blastomyces dermatitidis and Blastomyces gilchristii are thermally dimorphic fungi. Both grow as a mould form at 25°C (room temperature), and as a yeast form at 37°C (body temperature). Upon entering the body from the environment, the mould transforms into the yeast-phase as part of the adaptation process to a new environment with an elevated temperature. Unlike other fungi, the dimorphic fungi, including Blastomyces spp. are considered true pathogens and can cause disease in otherwise healthy individuals.

Clinical Presentation:

Blastomycosis is a fungal infection that primarily affects the lungs, but can become a systemic infection with extrapulmonary manifestations. Up to 50% of pulmonary cases remain asymptomatic. Pulmonary blastomycosis may be acute or chronic.

Acute pulmonary infection, which often goes undiagnosed, presents as an influenza-like illness with the sudden onset of fever, cough, and a pulmonary infiltrate on chest radiographs. The acute disease often resolves spontaneously after 1–3 weeks. A subset of those with acute infection will go on to severe disease and acute respiratory distress syndrome (ARDS).

Chronic pulmonary infection has a slow onset where initial symptoms of cough and chest pain may be mild or absent. Clinical manifestations may include 2–6 months of weight loss, fever, night sweats, cough with sputum and chest pain, and may be similar to tuberculosis, other fungal infections and cancer. There is a very high mortality rate for patients who develop ARDS with chronic pulmonary infection.

Extrapulmonary disease can occur in patients with blastomycosis, but is more common in patients with chronic pulmonary infection. The most common extrapulmonary site for infection is the skin (cutaneous lesions are often located on the face and distal extremities). Other common sites include bone, the genitourinary system, and the central nervous system, but any system can be affected.

Untreated, chronic and extrapulmonary blastomycosis can eventually progress to death, and a high index of suspicion is required for prompt treatment of all disease to prevent progression.

Modes of Transmission:

Inhalation of airborne spores in dust from the mould or saprophytic growth forms. Cases of blastomycosis from direct inoculation into the skin are rare, but can occur.

No person-to-person transmission or zoonotic transmission. Infection in animals, particularly dogs, has been identified, but animals do not appear to directly transmit the disease to humans.

Incubation Period:

The incubation period ranges between 21–106 days, with a median of 43 days.

Period of Communicability:

No person-to-person transmission, nor zoonotic transmission from infected animals. It is not known how long spores can retain their infectivity.


Risk Factors/Susceptibility

People who participate in outdoor activities in wooded areas (such as forestry work, hunting, and camping) in endemic areas may be at higher risk of exposure to Blastomyces spp. Susceptibility is general in areas where B. dermatitidis is present in the environment. Immunocompromised individuals have higher morbidity and mortality with blastomycosis infection.


Diagnosis and Laboratory Testing

Although urine antigen and serological testing is available, the sensitivity and specificity are poor, and therefore they are not generally recommended. If a patient has a reactive Blastomyces serology result, it is recommended that appropriate specimens be collected for microscopy and culture.

Testing Information & Requisition


Patient Information

Patient Fact Sheet


What Can Be Done about Blastomycosis?

Unfortunately, there is no vaccine against Blastomycosis. There is also no environmental control product to eradicate it from the soil. It cannot be seen. A pet or person can become infected in one location, and hundreds of others may be exposed to the same location and not become infected. When illness results, the symptoms usually arise weeks or even months after exposure, so pinpointing the location of exposure is very difficult in many cases.

Although there is no evidence to support use of any specific personal protective equipment (no proof it will definitely protect you), consider wearing work gloves, long pants and sleeves, enclosed footwear, a dust mask and eye protection when performing work that disturbs soil, especially when your face will be near the soil. Changing the amount and length of time you are exposed to soil dust may reduce risk.

Individuals whose immune system is weakened by chronic illness or medications should also consider avoiding exposure to disturbed soil, especially in moist, acidic areas.

Blastomycosis is much more common in Northwestern Ontario than in other parts of Ontario. If you have been outdoors in Northwestern Ontario and develop symptoms as described, or if you are starting a medication that will lower your immune system, tell your doctor you may have been exposed to the fungus that can cause Blastomycosis.



  1. Ministry of Health and Long Term Care, Infectious Diseases Protocol - Appendix 1 (2022) Blastomycosis.


Additional Resources

Government of Canada, “For Health Care Professionals: Blastomycosis,” 2016.


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