Histoplasmosis

Histoplasmosis in a canine spleen Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Histoplasma capsulatum

• Non-contageous, systemic mycosis

• Commonly pulmonary infections occur
  • Other organs can be involved
  • Involves the reticuloendothelial system
  • Intestinal form can also occur

• Acute and chronic disease can occur

• Endemic to the USA
  • Isolated cases have been reported in Europe

• Respiratory infection
  • Infection via ingestion can also occur

• Affects dogs, cats, cattle, horses and humans

• Found in soil contaminated by bird droppings, decaying vegetation and in caves inhabited by bats

Histoplasmosis lesions in lungs Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Fine, branching, septate hyphae with smooth-walled pyriform to spherical microconidia and large, thick-walled tuberculate macroconidia on simple conidiophores

• Dimorphic fungi

• Hard to demonstrate in smears as the organisms is very small
  • Stain with Giemsa or Wright and examine under oil immersion lens

• Present intracellularly in macrophages as oval yeast cells with few buds
  • Clear halo is seen around the darker staining central material

• Grows on Sabouraud's Dextrose agar
  • Creamy white colonies, turning tan coloured and then brown

• Also grows on Blood agar
  • Small, white yeast-like colonies

• Test using immunodiffusion, complement fixation and counterimmunoelectrophoresis
  • Skin test of little value as it only indicates exposure

• Treatment with Amphotericin B
  • If Amphotericin B is contra-indicated, imidazoles can be given orally

• The prognosis is poor in acute and disseminated cases

Histoplasmosis in a canine spleen using silver stain Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath Histoplasmosis phagocyte Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath Histoplasmosis tuberculate chlamydospores Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Caused by Histoplasma capsulatum
• Gross lesions in lungs:
  • Firm encapsulated granulomas (granulomatous pneumonia)
• Microscopic lesions:
  • Macrophages with inracytoplasmic yeasts
• Also in other tissues

Test yourself with the Systemic Mycoses Flashcards

Histoplasmosis Flashcards