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Blastomycosis

NCCID Disease Debriefs provide Canadian public health practitioners and clinicians with up-to-date reviews of essential information on prominent infectious diseases for Canadian public health practice. While not a formal literature review, information is gathered from key sources including the Public Health Agency of Canada (PHAC), the USA Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and peer reviewed literature.

This disease debrief was prepared by Jiayin (Emma) Xie. Questions, comments, and suggestions regarding this disease brief are most welcome and can be sent to nccid@manitoba.ca.

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Questions Addressed in this debrief:

  1. What are important characteristics of Blastomycosis?
  2. What is happening with current outbreaks of Blastomycosis?
  3. What is the current risk for Canadians from Blastomycosis?
  4. What measures should be taken for a suspected Blastomycosis case or contact?

Cause

Blastomycosis is a pulmonary, cutaneous or disseminated infection caused by the fungus Blastomyces dermatitidis (B. dermatitidis). This fungus exists in mold form in the environment; it produces microscopic fungal spores, particularly in moist soil and in decomposing matter such as wood and leaves. It can also exist in yeast form in human tissue. Blastomycosis enters the human body when a person breathes in air that contains microscopic fungal spores. After the spores enter air sacs in the lungs, human body temperature allows the spores to transform into yeast. The yeast can stay in the lungs or spread through the bloodstream to other parts of the body, such as the skin, bones and joints, organs, and the central nervous system (brain and spinal cord). Although 50% of people who breathe in the spores are asymptomatic, others will develop symptoms like fever and cough, and the infection can be fatal if it is not treated. Unlike other fungal infections, Blastomycosis not only occurs in immunocompromised patients but also in immunocompetent patients. Blastomycosis can also infect pets like cats and dogs, but it is not communicable from person to person or animal to person, except in rare cases of perinatal or sexual transmission.

Signs and Symptoms

The time between exposure to the spores and when symptoms develop varies widely, ranging from 21 to 100 days. Spring and summer exposure are often followed by symptomatic presentation in fall or winter, which can delay diagnosis, since patients may not mention sources of exposure that occurred months before. The signs and symptoms of blastomycosis vary among individuals, from asymptomatic infection to life-threatening complications such as respiratory distress syndrome. Common symptoms of blastomycosis include: cough or cough with blood, fever, shortness of breath, chills and/or night sweats, fatigue, weight loss and poor appetite, joint or bone pain, back or chest pain and wart-like skin growths, ulcers and abscesses. Many patients are first diagnosed with bacterial pneumonia because the symptoms are similar.

Severity and Complications

About 50% of infections are asymptomatic or mild, and resolve without treatment. However, some patients develop a chronic lung infection and/or disease spread to other areas of the body. Severe pulmonary disease and extrapulmonary disease are more likely in patients with impaired immune systems. Disseminated Blastomycosis occurs in approximately 25%-30% of the patients; this is caused by the yeast entering the bloodstream via the lungs. The skin is the most common site of extrapulmonary disease. Primary cutaneous blastomycosis, though rare, can occur when there is direct inoculation after trauma to the skin. Cutaneous blastomycosis causes wart-like growths or open sores, primarily on the face, hands and feet. Abscesses can involve any organ, although they are most commonly found in the skin.

Epidemiology

General:

Blastomycosis is predominantly a disease of North America. In Canada it is endemic in the provinces that border the Great Lakes and the Saint Lawrence Riverway. In Manitoba, the Seine River, Whiteshell, and Lake of the Woods have the highest prevalence of Blastomycosis. The disease is hyper-endemic in north-western Ontario. Incidences of blastomycosis appear to be increasing these regions, and are most frequently diagnosed during cold weather in Manitoba and Ontario. In Ontario, 309 cases were reported between 1994 and 2003. In Manitoba, 143 cases were reported between 1988 and 1999. The annual incidence rate of blastomycosis in Saskatchewan, Manitoba, Ontario and Quebec is 0.62 cases per 100,000 population. In areas of endemicity, the annual incidence of blastomycosis requiring hospitalization is 3 to 6 cases per million persons. Knowledge regarding the epidemiology of sporadic, asymptomatic infection with B. dermatitidis is lacking, hence all the aforementioned epidemiology is based on recognition and reporting of symptomatic cases.

Although the majority of cases are sporadic or endemic, epidemics of blastomycosis associated with exposure to a common outdoor source are documented in the United States. The ecological niche for B. dermatitidis is wet earth that has been enriched with animal droppings, rotting wood, and other decaying vegetable matter. Men are affected more frequently than women and children, because men are more likely to participate in activities that expose them to fungal spores, such as digging or moving rotting wood. B. dermatitidis is not transmitted from person to person and is not contagious. Sex, age, and race do not directly affect susceptibility to blastomycosis, but rather represent variables that influence the likelihood of exposure to B.dermatitidis in the environment.

Clinical and Laboratory Diagnosis:

There are currently no methods to test soil for the presence of Blastomyces species. The absence of sensitive and specific serologic assays and the use of inadequate skin test reagents have hindered efforts to fully define the epidemiology of Blastomycosis, the understanding of which is based primarily upon case series. Perhaps more importantly, B. dermatitidis has been isolated only infrequently from environmental sources, and thus the ecology of B. dermatitidis remains incompletely understood.

If symptoms and patient activity history suggests possible infection, diagnosis can be made by microscopic visualization and culture of the organism. Thick-walled, figure-of-eight shaped, broad-based, single-budding yeast forms may be seen in urine, sputum, tracheal aspirates, cerebrospinal fluid, and material from lesions, processed with 10% potassium hydroxide or a silver stain.

Enzyme Immunoassay (EIA) measures cell wall-derived antigen in serum or urine with good sensitivity, particularly in severe or disseminated disease. However, cross-reactions may occur with other endemic fungal infections. An enzyme immunoassay (EIA) is available for detection of Blastomyces dermatitidis antigen in urine, blood and other bodily fluids.

Prevention and Control

Illness caused by blastomycosis can be minimized by early recognition and appropriate treatment of the disease. Awareness of the disease by both the public and health care providers is the key to early diagnosis. It may not be possible to completely avoid exposure to the fungus that causes blastomycosis in areas where it is endemic. People who have weakened immune systems should consider avoiding wooded areas, and activities that involve disrupting soil in these areas. Wearing a face mask can minimize breathing in fungal spores.  

Vaccination

There is no vaccination to prevent blastomycosis.

Treatment

Re-emergence of infection can occur after treatment; for this reason, a prolonged course of antifungal medications (at least 6 months) is recommended. Itraconazole is the treatment of choice for less severe or moderate disease. Amphotericin B or Amphotericin B deoxycholate are used for more severe infections, and may be given with Itraconazole as well. The recommended treatment regime for less severe or moderate disease is 600 mg of Itraconazole given orally daily for three days, followed by 200 mg to 400 mg per day for 6 to 12 months. Itraconazole has relatively low toxicity and good efficacy, though it is important to remember that gastric acidity is required for its absorption. Other azoles, including ketoconazole and fluconazole, can be used but are not preferred due to lower efficacy. Antibiotics do not work against blastomycosis since it is a fungal, rather than bacterial, illness.

There were 581 hospitalizations for blastomycosis reported in Ontario over the 2006-2015 period, 245 (42%) of which were in northwestern Ontario. The average hospitalization rate for blastomycosis in northwestern Ontario was 35.0 per 100,000 per year. This rate varied from 1.7 in the Red Lake region to 57.9 in the Kenora region. In Manitoba, 143 cases were reported between 1988 and 1999.

The annual incidence rate of blastomycosis is 0.62 cases per 100,000 people in the Canadian provinces of:

  • Ontario
  • Quebec
  • Manitoba
  • Saskatchewan

Data is not available in other Canadian provinces but the relative risk is likely low since the fungus is most prevalent around the Great Lakes; however, cases related to travel in endemic areas may occur.

Overall risk to Canadians is low, but risk is higher in areas of endemicity, where the annual incidence of blastomycosis requiring hospitalization is 3 to 6 cases per million persons. Risk in Northwestern Ontario and Eastern Manitoba is significantly higher.

Manitoba

Clinical cases are to be reported to the local Public Health Unit or Health Links-Info Santé at 1-888-315-9257 or 204-788-8200. Completion and return of the Communicable Disease Control Investigation Form is generally not required, unless otherwise directed by a Medical Officer of Health.

  • Blastomycosis – Manitoba Communicable Disease Management Protocol

Ontario

Clinical cases are to be reported to the Ontario Northwestern Health Unit at 1-800-830-5978 or 807-468-3147 or by completing the Ontario Investigation Tools (OITs)

Canada

There is no protocol for suspected cases in the other provinces and territories.