Blastomycosis

• North America
  • Most common in the North-Central and South-Eastern states

• Caused by Blastomyces dermatitidis

• Widespread in soil

• Respiratory infection

• Lesions start in the lungs
  • Haematogenous dissemination
  • Can be found in lesions in the eyes, brain, bones and genitalia
  • Fatal if not treated

• Lesions are also found on the skin
• These may ulcerate

• Granulomatous nodules

• Affects mainly dogs (and humans)
  • Can affect cats, horses, dolphins, ferrets and sealions but is rare in these species

• Microscopically:
  • Large, spherical, thick-walled cells
  • Single buds connected to a mother cell by a wide base
  • Double contoured effect of cells

• Grows on Sabauraud's Dextrose and Blood agar
  • On Sabauraud's Dextrose colonies appear moist and grey with a white cotton-like mycelium which turns tan, brown and then black
    • Septate hyphae
    • Small, oval/pyriform conidia
    • Older cultures have thickened walls
  • On Blood agar colonies are creamy in colour, waxy and wrinkled
    • Thick-walled budding yeast cells can be seen

• Diagnosis:
  • Complement fixation test
  • Falling antibody titres indicate a poor prognosis
  • ELISA and counterimmunoelectrophoresis can also be used

• Treatment:
  • Amphotericin B
  • Imidazoles