Blastomycosis

Key Messages

  • Blastomycosis is an infection resulting from inhalation of Blastomyces fungal spores found in moist soil and decaying organic matter.
  • In Canada, exposure can occur in the provinces bordering the Great Lakes and St. Lawrence Seaway.
  • Pulmonary and extrapulmonary manifestations are possible.
  • There is no person-to-person transmission.
  • Consultation with an infectious diseases specialist is recommended.
Introduction

Blastomycosis refers to disease caused by the fungi Blastomyces dermatiditis and Blastomyces gilchristii. These are dimorphic fungi which grow in mould form at 25–28 degrees Celsius, and in yeast form at 37 degrees Celsius. Currently it is not known if there are biological or clinical differences between B. dermatiditis and B. gilchristii; thus this summary will refer to the etiologic agent of blastomycosis as B. dermatiditis.

Infection with B. dermatiditis 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.

Local Epidemiology

Blastomyces species lives in the environment; particularly in moist soil and decaying organic matter (e.g., wood and leaves). Exposure to B. dermatiditis occurs mostly in those living in the Midwestern, southeastern, and south central United States, as well as in the Canadian provinces bordering the Great Lakes and St. Lawrence Seaway. The incidence in Ontario is noted to be on the rise.

A recent 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).

Table: Geographic distribution of blastomycosis in Ontario, PHOL data, 1995–2015*

Average annual incidence rate of blastomycosis/100,000 population

Ontario Local Health Integration Network (LHIN)

0.030–0.075

Erie St. Clair; South West; Waterloo Wellington; Hamilton Niagara Haldimand Brant

0.076–0.161

Mississauga Halton; Central East; South East

0.162–0.422

Central West; Toronto Central; Central; North Simcoe Muskoka; Champlain (includes Ottawa)

0.423–0.867

North East

0.868–10.938

North West

*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.).

Beyond these reports our local epidemiologic data is limited as blastomycosis was added to the Ontario reportable disease list in July 2018 after having been delisted by the province in 1989.

Signs and Symptoms

Infection with Blastomyces species is asymptomatic in up to 50 per cent of cases. When associated with clinical disease, there can be a wide range of clinical presentations following an incubation period from 2 weeks to 3 months. 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. Organ-specific disease most commonly affects the lungs, skin, bone, genitourinary system, and central nervous system, although infection can occur in any organ system.

Pneumonia is the most common presentation of blastomycosis. Symptoms can be similar to an acute bacterial pneumonia (fevers, chills, cough productive of sputum, hemoptysis) or, more frequently, a chronic pneumonia syndrome (weight loss, night sweats, fever, productive cough, hemoptysis over a period of 2 to 6 months).

Skin manifestations are the next most common, and 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.

Diagnosis/Laboratory Testing
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 see Public Health Ontario’s Fungus Culture – Reference Identification and Labstract on systemic mycoses.

Serology can also be sent for Blastomyces species; however, due to cross-reactivity of the test with other endemic mycoses, as well as lack of sensitivity of the test, serology is difficult to rely on for diagnosis. Please see Public Health Ontario’s Fungal – Serology. Similarly urinary antigen for Blastomyces species can cross-react with Histoplasma species, thus leading to false positives, and a negative test is unreliable due to a high rate of false negatives.

All patients with suspected blastomycosis infection, either pulmonary or extra-pulmonary, should have a chest x-ray done to assess for lung involvement.

Reporting Requirements

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.

Management

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.

Prevention

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. 

Public Health Role

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.

Patient Information
Physician Resources

Ottawa Public Health

Public Health Ontario

Ministry of Health and Long-Term Care

Health Canada

US CDC

Infectious Diseases Society of America (IDSA) Guidelines on management of blastomycosis

Additional Reading:

  1. Chapman SW, Dismukes WE, Proia LA, et al. Clinical Practice Guidelines for the Management of Blastomycosis: 2008 Update by the Infectious Diseases Society of America. Clin Infect Dis 2008;46(12):1801–1812.
  2. Mandell, Douglas, and Bennett’s Principles of Infectious Diseases, Eight Edition. Chapter: Blastomycosis (p. 2963–2973).
  3. Heymann DL, ed. Control of Communicable Diseases Manual, 20th Edition. APHA Press, Washington, DC; 2015: 69–71.
  4. American Academy of Pediatrics. Blastomycosis. In: Kimberlin DW, Brady MT, Jackson MA, Long SS, eds. Red Book: 2018 Report of the Committee on Infectious Diseases. 31st ed. Itasca, IL: American Academy of Pediatrics; 2018: 249–251.

Contact Us

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.

Contact Us