Blastomycosis

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  • 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


  • Caused by Blastomyces dermatitidis
  • Occurs mainly in the Americas, Middle East and Africa, occasionally in Europe
  • Mainly in young dogs, occasionally other species
  • Can involve almost any tissue after spread from lungs
  • Gross lesions:
  • Microscopic lesions:
    • Yeast fungi with thich walls in nodules with macrophages, neutrophils and giant cells