Blastomycosis is the infection caused by the thermically dimorphic fungus Blastomyces. It is most commonly found in North America, including the midwestern United States (e.g., Wisconsin, Minnesota), the southcentral and southeastern United States (mainly around the Ohio and Mississippi River Valleys, Great Lakes, Saint Lawrence River basin), as well as adjacent provinces of Canada, including Ontario, Saskatchewan, Quebec and Manitoba. Emerging areas in the United States include upstate New York and Vermont. Autochthonous infections have been described throughout Africa (>150 reported cases), the Middle East (~12 reported cases), and India (<12 reported cases). 

Humans acquire blastomycosis by inhaling aerosolized conidia (spores) and mycelial fragments present in warm, moist soil within wooded areas that are rich with organic material. Many individuals (not always) have a history of recreational, construction, or occupational exposures to wooded areas close to freshwater bodies (e.g., lakes, rivers). Although most cases of blastomycosis are sporadic (e.g., 1 person infected), over 20 outbreaks have been reported in North America.

Most cases are asymptomatic (~50%). After an incubation period of 3 weeks-3 months, persons that develop symptomatic infection can present with subclinical or self-limiting disease, acute or subacute pneumonia, acute respiratory distress syndrome, miliary pneumonia, or chronic pneumonia. Latent infection in blastomycosis is thought to be uncommon.

One thing to remember about blastomycosis compared with the other endemic mycoses, is its tendency to disseminate outside of the lungs.  Approximately 15-53% of cases disseminate to other organs including the skin (most common extra-pulmonary site), bone, genitourinary (prostate) or central nervous system. Unlike other dimorphic fungi, disseminated blastomycosis occurs at similar rates between immunocompetent and immunocompromised persons. Here’s a summary for you:

• Pulmonary blastomycosis: 
• • Acute pulmonary blastomycosis: (~50% asymptomatic). Mimics acute bacterial pneumonia. Typically patients are treated with multiple courses of antibiotics for community-acquired pneumonia with no improvement. Reactivation from prior infection and reinfection is uncommon (unlike other endemic mycosis). 
  • Chronic pulmonary blastomycosis: mimics tuberculosis or malignancy and can appear as a mass-like or cavitary lesion.

• Extrapulmonary blastomycosis (15-53%): occurs through lymphohematogenous spread and often occurs concurrently with pulmonary blastomycosis.
  • Cutaneous disease: (most common site of dissemination). Lesions can be verrucous or ulcerative. Lesions can be misdiagnosed as basal cell carcinoma or pyoderma gangrenosum. 
  • Osteomyelitis: virtually any bone can be infected but most common are the vertebrae, pelvis, skull, ribs and long bones. There can be contiguous soft tissue abscesses or chronic draining sinuses. 
  • Genitourinary: prostatitis, epididymitis.
  • Central nervous system (CNS): meningitis (neutrophilic or lymphocytic predominance on CSF), mass lesion, or abscess. CNS infection is uncommon; however, it is more common among certain immunocompromised individuals.

Suspect blastomycosis in an individual living in or traveling from an endemic area with a compatible clinical syndrome and exposure history, especially in those with pneumonia that does not respond to antibiotics, pneumonia with skin lesions, and acute respiratory distress syndrome. In addition, blastomycosis should be suspected in patients who have a family member or pet (e.g., dog) diagnosed with blastomycosis, which indicates a common source of environmental exposure - beware pet owners!!!. Blastomyces is less likely compared with other endemic fungi (but not impossible) to reactivate years after primary exposure. Diagnosis is supported by:

• Antigen testing: from urine, serum, bronchoalveolar fluid, or cerebrospinal fluid. Careful because it has substantial cross-reactivity with other endemic fungi, such as Histoplasma, Paracoccidioides and Talaromyces!
• Serology: it is unfortunately not a great test (low sensitivity), but can be useful as an adjunct to the antigen testing.
• Histopathology with staining: identify yeast with a doubly refractile cell wall with broad-based budding between mother and daughter cells. 
• Culture: Takes 2-4 weeks to grow.

All persons with blastomycosis require treatment with antifungal therapy regardless of infection severity. This is in contrast to histoplasmosis and coccidioidomycosis in which clinical monitoring can be considered for some mild forms of disease. The rationale for treating all persons with blastomycosis is to prevent dissemination! which is common in immunocompetent and immunocompromised persons. Prior to starting treatment, all females of child-bearing age should undergo pregnancy testing because azole antifungals are teratogenic and increase risk for spontaneous abortion. 

• Mild-moderate cases: itraconazole → suggest monitoring levels. (alternatives: voriconazole, posaconazole, isavuconazonium sulfate).
• Severe cases: liposomal amphotericin B for 1-2 weeks (exception: CNS disease 4-6 weeks) followed by oral azole therapy, typically itraconazole (alternatives: voriconazole, posaconazole, isavuconazonium sulfate).
• Pregnancy: liposomal amphotericin B for 6-8 weeks. Avoid azole antifungal therapy. 
• Duration: ≥6 months for most cases of pulmonary blastomycosis, but ≥12 months may be needed in special situations (e.g., cavitation, disseminated disease). Total duration is tailored to clinical, and radiographic response of each patient.

Guidelines: IDSA Clinical Practice Guideline Update for the Management of Blastomycosis (2008)

For patients: Handout from the American Thoracic Society