NAME: Blastomyces dermatitidis
SYNONYM OR CROSS REFERENCE: Blastomycosis Footnote 1, Gilchrist’s disease.
CHARACTERISTICS: Dimorphic fungus that exists in mold form in the environment or at 25°C, and in yeast form in human tissue or at 37°C Footnote 2. The microconidia are oval or pyriform (pear shaped), with a diameter of 2 to 10 µm, and no macroconidia are produced. The yeast cells, characterized by large budding forms, are large, round, and thick-walled, with a diameter of 5 to 15 µm Footnote 3, Footnote 4. Microconidia, produced from hyphae of the mycelial form, are infectious for humans Footnote 1, Footnote 2, Footnote 5.
PATHOGENICITY/TOXICITY: Infection develops when conidia of B. dermatitidis are aerosolized from soil, inhaled into the lungs, and deposited into pulmonary alveoli Footnote 2. In the lungs, B. dermatitidis converts to yeast form, triggering the hosts inflammatory response at the site of infection. Yeast that are not phagocytised and cleared by the host are able to spread via blood or lymphatics to other sites in the body. Infection with B. dermatitidis can cause blastomycosis, which can be pulmonary, cutaneous, or disseminated. Clinical manifestations can range from mild chronic cough to acute respiratory distress syndrome-like symptoms Footnote 6. Infection can be asymptomatic or subclinical if the host immune defences limit disease. Some patients will progress to a chronic form of pneumonia Footnote 1, Footnote 2, Footnote 5. Skin lesions can be nodular, verrucous, or ulcerative, often with minimal inflammation but can rapidly grow into a superficial ulceration with a granulomatous base, and are generally located around the face and distal extremities Footnote 7. Abscesses are often subcutaneous, but can involve any organ. Disseminated blastomycosis usually begins with pulmonary infection and can involve skin, bones, central nervous system (CNS), abdominal viscera, and kidneys. Intrauterine or congenital infections occur rarely Footnote 2, Footnote 5. Severe pulmonary and disseminated diseases are more likely when cellular immunity is impaired Footnote 2, Footnote 4, Footnote 8. The mortality rate is 0 – 2% in treated patients, and 42% without treatment Footnote 9.
EPIDEMIOLOGY: Blastomycosis may be epidemic or sporadic and has been reported in the United Kingdom, United States, Canada, central Europe, Africa, Siberia, Saudi Arabia, Israel, and India Footnote 10. Blastomycosis is more common in North America, endemic to the Midwestern, south-eastern, and south central United States along the Ohio and Mississippi rivers. B. dermatitidis is also prevalent in soil near the Great Lakes, lakes in the Canadian shield, and St. Lawrence seaway, such as northern New York and the southeast Canadian provinces, where the annual incidence rate is 0.62 cases per 100,000 population Footnote 1, Footnote 2, Footnote 5, Footnote 11-Footnote 13. Three to six cases of blastomycosis requiring hospitalization occur per million persons per annum in areas of endemicity Footnote 1. Outbreaks have been associated with occupational and recreational activities, often along streams or rivers, and have resulted from exposures to moist soil enriched with decaying vegetation Footnote 4. Blastomycosis is more commonly seen in adults than children and more men than women are affected Footnote 4.
INFECTIOUS DOSE: Unknown.
MODE OF TRANSMISSION: The primary mode of transmission is through inhalation. B. dermatitidis is found in the soil and saprophytic molds, which enter the body primarily through inhalation of conidia into the respiratory tract Footnote 2, Footnote 17. Accidental inoculation, dog bites, conjugal transmission, and intrauterine transmission are also reported routes of transmission but occur relatively rarely Footnote 18.
DRUG RESISTANCE: Strains have been identified to be resistant to hygromycin B and chlorimuron ethyl Footnote 21.
SUSCEPTIBILITY/RESISTANCE TO DISINFECTANTS: B. dermatitidis is susceptible to sodium hypochlorite Footnote 22, peracetic acid, phenolic compounds, quaternary ammonium compounds, hydrogen peroxide vapor (for at lest 30 min) Footnote 23, formaldehyde Footnote 22, Footnote 24, formalin, and iodophors Footnote 22, Footnote 25. In addition, most fungi are also susceptible to hydrogen peroxide and glutaraldehyde Footnote 24, Footnote 26.
PHYSICAL INACTIVATION: While information specific to B. dermatitidis is unavailable, most fungi are inactivated by moist heat (121°C for at least 15 min) or dry heat (160-170°C for 1-2 hours) Footnote 27, Footnote 28.
SURVIVAL OUTSIDE HOST: The natural habitat of B. dermatitidis is the soil. It appears to survive best in moist acidic soils that contain a high nitrogen and organic content. Higher soil temperatures and recent rainfall facilitate growth of the fungus Footnote 4.
SURVEILLANCE: Monitor for symptoms. 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 sputum, tracheal aspirates, cerebrospinal fluid, urine, or material from lesions processed with 10% potassium hydroxide or a silver stain Footnote 2, Footnote 5, Footnote 16. An enzyme immunoassay (EIA) is available for detection of B. dermatitidis antigen in urine, blood, and other body fluids. EIA measures cell wall-derived antigen in serum or urine with good sensitivity, particularly in the setting of severe or disseminated disease, but cross-reactions may occur with other endemic fungal infections Footnote 5, Footnote 16.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Treat with appropriate drug therapy. Itraconazole is commonly used for less severe infections; while amphotericin B or amphotericin B deoxycholate are used for more sever infections, sometimes with the addition of itraconazole Footnote 5, Footnote 20.
LABORATORY-ACQUIRED INFECTIONS: At least 11 reported laboratory-acquired infections with two deaths Footnote 29, Footnote 30. Blastomycosis has been acquired in the laboratory as a result of transcutaneous inoculation of the yeast form and from inhalation of conidia. Human infection acquired from tissue of infected animals has been reported.
SOURCES/SPECIMENS: Sputum, tracheal aspirates, cerebrospinal fluid, urine, blood, material from lesions, and tissues of infected animals Footnote 5.
PRIMARY HAZARDS: Yeast forms may be present in the tissues of infected animals and in clinical specimens; parenteral inoculation of these materials may cause granulomas Footnote 31. Inhalation of infectious mold conidia in aerosols can also be an infection hazard Footnote 17.
RISK GROUP CLASSIFICATION: Risk Group 3 Footnote 32.
CONTAINMENT REQUIREMENTS: Containment Level 3 facilities, equipment, and operational practices for work involving infectious or potentially infectious material Footnote 33.
PROTECTIVE CLOTHING: Personnel entering the laboratory should remove street clothing and jewellery, and change into dedicated laboratory clothing and shoes, or don full coverage protective clothing (i.e., completely covering all street clothing). Additional protection may be worn over laboratory clothing when infectious materials are directly handled, such as solid-front gowns with tight fitting wrists, gloves, and respiratory protection. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 33.
OTHER PRECAUTIONS: All activities with infectious material should be conducted in a biological safety cabinet (BSC) or other appropriate primary containment device in combination with personal protective equipment. Centrifugation of infected materials must be carried out in closed containers placed in sealed safety cups, or in rotors that are loaded or unloaded in a biological safety cabinet. The use of needles, syringes, and other sharp objects should be strictly limited. Open wounds, cuts, scratches, and grazes should be covered with waterproof dressings. Additional precautions should be considered with work involving animals or large scale activities Footnote 33.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up.
DISPOSAL: Decontaminate, either by steam sterilization, incineration, or chemical disinfection before disposal Footnote 33.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled Footnote 33.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: October 2010
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting form the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2010