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Key Messages
- Blastomycosis is an infection resulting from inhalation of Blastomyces fungal spores found in moist soil and decaying organic matter.
- Risk areas range from Saskatchewan to Quebec, particularly bordering the Great Lakes, the St. Lawrence Seaway, and Canadian Shield lakes; in the United States in the Ohio and Mississippi River valleys and eastwards. Pulmonary and extrapulmonary manifestations are possible. Consider blastomycosis in patients who present with a respiratory syndrome and skin lesions.
- There is no person-to-person transmission.
- Consultation with an infectious diseases specialist is recommended.
| Introduction | ||||||||||||
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Blastomycosis refers to disease caused by fungi of the Blastomyces genus. These are dimorphic fungi which grow in mould form at 25 to 28 degrees Celsius, and in yeast form at 37 degrees Celsius. Blastomyces dermatitidis and Blastomyces gilchristii are the most common species associated with Blastomycosis. Within the last decade, several other species of the Blastomyces genus have been identified. While some have only been identified internationally, B. helicus has been found in areas bordering the Rocky Mountains of western North America. Although there are genetic differences between the species, there are no clinically relevant differences, and differentiation may not be attempted in clinical laboratories. This summary will refer to the etiologic agent of blastomycosis as Blastomyces species. Infection with Blastomyces species occurs when the organism’s conidia (fungal spores) are inhaled into the host’s lungs. Upon entering the body from the environment, the mould form of the agent moves into the yeast phase due to the change in temperature. From here, both pulmonary and extrapulmonary manifestations can occur. There is no person-to-person transmission. |
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| Local Epidemiology | ||||||||||||
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Blastomyces is a moist soil and decaying organic matter associated fungus. Risk areas for exposure to B. dermatiditis range from Saskatchewan to Quebec, particularly bordering the Great Lakes, the St. Lawrence Seaway, and Canadian Shield lakes; in the United States in the Ohio and Mississippi River valleys and eastwards The diagnosis of blastomycosis is often protracted because this fungal infection is uncommon and its symptoms non-specific. Ontario added blastomycosis to its reportable disease list mid-2018. Local acquisition in Ottawa may be on the rise. In each year of 2019 to 2021, Ottawa Public Health (OPH) received 4 reports of blastomycosis; however, for illness onsets in 2022, to date OPH has received 10 reports for an incidence rate of 0.93 per 100,000 population. In Ontario to date, in 2022 the average incidence was 0.59/100,000, though in Northwestern Ontario, a hyperendemic area for blastomycosis, the incidence was 50/100,000. A review of Public Health Ontario Laboratory (PHOL) 1995 – 2015 data (Brown EM, McTaggart LR, Dunn D, et al. Epidemiology and Geographic Distribution of Blastomycosis, Histoplasmosis, and Coccidioidomycosis, Ontario, Canada, 1990–2015. Emerging Infectious Diseases. 2018;24(7):1257-1266. doi:10.3201/eid2407.172063) found the following regarding the geographic distribution of blastomycosis in Ontario (Table).
*Data from Figure 1 of Brown et al., 2018. Brown et al. additionally described that two-thirds of cases were males, and all age groups were affected with a modest peak in those 40–49 years of age. Two paediatric cases were in infants less than or equal to one year of age. Further findings included an increasing incidence from 1995 to 2002, primarily attributable to the North West region of Ontario, with relatively stable rates thereafter to 2015. When smaller geographic areas than those represented in the Table are considered, in the North West LHIN, hospitalization rates were as high as 57.9/100,000 per year between 2006 and 2015 (Litvinjenko S, Lunny D. Blastomycosis hospitalizations in northwestern Ontario: 2006–2015. Can Commun Dis Rep. 2017;43(10):200-5.). |
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| Signs and Symptoms | ||||||||||||
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Infection with Blastomyces species is asymptomatic in up to 50 per cent of cases. Incubation periods between exposure and clinical disease are typically 2 weeks to 3 months. Rarely, an incubation period may last many months to years due to reactivation or latent infections. When associated with clinical disease, there can be a wide range of clinical presentations. Blastomycosis can be difficult to diagnose as symptoms can be easy to mistake for other more common illnesses. Non-specific symptoms can include fever, malaise, fatigue, and weight loss. Pneumonia is the most common presentation of blastomycosis, occurring in up to 90% of symptomatic cases. Symptoms can be similar to an acute bacterial pneumonia (fevers, chills, cough productive of sputum, hemoptysis) and can progress to acute respiratory distress syndrome in up to 15% of hospitalized patients. More frequently, patients develop a chronic pneumonia syndrome (weight loss, night sweats, fever, productive cough, hemoptysis over a period of 2 to 6 months). Disseminated disease is common and can occur in 25% to 40% of all symptomatic patients. Although it is possible to develop blastomycosis through direct inoculation (e.g., from trauma), the vast majority of extrapulmonary manifestations are due to disseminated disease following a pulmonary infection. Disseminated disease most commonly affects the skin, bone, genitourinary system, and central nervous system, although infection can occur in any organ system. Skin manifestations are the most common extrapulmonary finding, occurring in 40% to 80% of cases with disseminated disease. Skin manifestations can take on two major forms: verrucous and ulcerative lesions. The verrucous lesions have an elevated heterogeneous border and the lesions appear crusted overtop of an abscess in the underlying subcutaneous tissue. The ulcerative lesions are usually open with draining exudate. Bone infection is most commonly reported in the vertebrae, pelvis, sacrum, skull, ribs, and long bones, but theoretically any bone can be involved. The most common forms of genitourinary blastomycosis are prostatitis and epididymo-orchitis. Meningitis or cerebral abscess are the most common neurologic manifestations of blastomycosis, with abscess formation having a predilection for the cerebellum. |
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| Diagnosis/Laboratory Testing | ||||||||||||
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Culture remains the gold-standard for diagnosing Blastomycosis. Direct detection of appropriately-sized, broad-based budding yeast with microscopy is a presumptive positive and remains an important part of the diagnostic algorithm. B. dermatitidis is most commonly identified via microscopy from sputum, tissue, or wound exudate specimens. The organism can also be visible on histology using special fungal stains. Please look under “F” at Public Health Ontario’s Test Information Index and also see the Labstract on systemic mycoses. Serology can also be sent for Blastomyces species; however, while relatively specific for detecting antibodies to Blastomyces, due to the lesser sensitivity of the test, serology is difficult to rely on for diagnosis – a negative result does not rule out the possibility of current infection. Please see Public Health Ontario’s Fungal – Serology. PHO also offers additional information at Blastomycosis in Ontario. All patients with suspected blastomycosis infection, either pulmonary or extra-pulmonary, should have a chest x-ray done to assess for lung involvement |
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| Reporting Requirements | ||||||||||||
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If you have a suspected or confirmed case of blastomycosis, it should be reported as soon as the next business day by fax or telephone: Monday to Friday from 8:30 am to 4:30 pm: Call 613-580-2424, extension 24224 or fax 613-580-9640. See also: Reporting a communicable disease. |
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| Management | ||||||||||||
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In the immunocompetent host, acute pulmonary blastomycosis can be a mild, self-limited illness that does not require treatment. Referral to an infectious diseases specialist should be considered in all cases of confirmed or suspected blastomycosis as treatment may still be offered in these circumstances in order to prevent development of disseminated infection. All immunocompromised patients, those with moderate to severe symptoms, or those with disseminated (extrapulmonary) disease should be offered antifungal therapy. The choice of antifungal therapy is dependent on the location and severity of disease and tailored based on independent host factors. Intravenous amphotericin B is the initial treatment of choice for those with moderate to severe pulmonary disease, disseminated blastomycosis, or disease involving the central nervous system. It is also the treatment of choice for immunocompromised patients with blastomycosis. Once clinical improvement has been noted with intravenous amphotericin B, oral step-down to itraconazole for the remainder of therapy is reasonable. The duration of suggested therapy ranges from 6 to 12 months depending on the site of disease. For those who present with mild acute pulmonary disease, initiating therapy with oral itraconazole is reasonable; again, consultation with an infectious diseases specialist is recommended. |
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| Prevention | ||||||||||||
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Preventive measures are not yet fully understood. It is possible, particularly for immunocompromised persons, that risk of infection may be reduced by avoiding activities that cause disruption of the soil. There is currently no approved vaccine against blastomycosis. |
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| Public Health Role | ||||||||||||
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Reporting to public health is important, as the incidence of blastomycosis in Ontario may be increasing. If endemic areas are able to be identified by reporting of disease, strategies to improve awareness among residents as well as healthcare providers of these areas can be put into place. |
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| Patient Information | ||||||||||||
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General Information on Blastomycosis Blastomycosis, Health Canada International Resources on Blastomycosis Blastomycosis, U.S. Centers for Disease Control and Prevention (CDC)
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| Physician Resources | ||||||||||||
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Lab Testing Go to Test Information Index | Public Health Ontario and click on “F” to see results for “Fungal” and “Fungus” General Information on Blastomycosis Infectious Diseases Protocol, Ontario Ministry of Health Blastomycosis in Ontario, Public Health Ontario Blastomycosis, Health Canada Pathogen Safety Data Sheet – Blastomyces dermatitidis, Health Canada International Resources on Blastomycosis Blastomycosis, U.S. Centers for Disease Control and Prevention (CDC) Guidelines on management of blastomycosis, Infectious Diseases Society of America (IDSA) |
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