Blastomycosis

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Basics

Description

  • Systemic pyogranulomatous disease caused by inhalation of spores (conidia) from the fungus Blastomyces dermatitidis or Blastomyces gilchristii (1,2)
  • ≥50% asymptomatic or minimally symptomatic
  • Heterogeneous severity, symptoms, and duration (1,2)
  • Pulmonary disease
    • Localized to the lungs in 70–80% of all cases
    • Acute pneumonia
    • Acute respiratory distress syndrome (ARDS)
    • Chronic pneumonia: indistinguishable from tuberculosis (TB), other fungal infections, lung cancer, other granulomatous disease
  • Disseminated (20–30% of all cases)
    • Cutaneous (40–80%)
    • Skeletal (25%)
    • Prostate, genitourinary (10–20%)
    • Meninges and brain (5–10%)
    • Virtually any organ or tissue
  • Rare direct inoculation skin disease
  • Synonym(s): Gilchrist disease; Chicago disease; North American blastomycosis

Epidemiology

  • Predominant sex: male (55–65%)
  • Predominant age: middle age
  • Overrepresented in patients of Asian descent
  • 10% of cases in children from endemic areas of North America
  • Most commonly acquired through inhalation of spores from contaminated soil in wooded areas (decaying vegetation) and rural or urban watersheds
  • Often infects otherwise healthy individuals engaging in outdoor activities

Incidence
1 to 40 cases per 100,000 populations in areas with endemic disease

Prevalence
Endemic areas: Midwestern, Southeastern, and South Central United States; Great Lakes region of United States and Canada; and the St. Lawrence Seaway. Recent hyperendemic areas include northern/central Wisconsin and northwestern Ontario, but outbreaks and case clusters continue to occur in multiple areas.

Etiology and Pathophysiology

Inhalation of airborne conidia (spores) from natural soil habitat. Phagocytosis of conidia by neutrophils and alveolar macrophages. Conidia transform to yeast phase (thermal dimorphism) within the lungs. Multiplication occurs within the lungs with potential dissemination through the blood and lymphatics to other organs. Pyogranulomatous inflammatory response leads to granuloma formation.

  • Dimorphic fungus: B. dermatitidis or B. gilchristii
  • Yeast at body temperature, generally 8 to 20 μm in size, with single-round, thick, double-retractile wall; single broad-based bud and scar; and multiple nuclei
  • Mold with delicate septate hyphae; pear-shaped conidia, found singly/at tips of conidiophores
  • Virulence varies by strain.
  • Incubation period: 45 days (range from 21 to 106 days)

Genetics
No known genetic predisposition

Risk Factors

  • Exposure to infected soil, especially along waterways, in areas with endemic disease
  • Excavation or digging in endemic areas
  • Risk for aggressive disease in immunocompromised states: HIV/AIDS, corticosteroids, cancer, chemotherapy, organ transplant; up to 40% of patients with AIDS have central nervous system (CNS) disease.

General Prevention

No proven measures; immunocompromised may consider avoiding soil-disturbing activities in locations where the fungus is known to be prevalent.

Commonly Associated Conditions

Diabetes mellitus

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