Canis ISSN: 2398-2942

Histoplasma capsulatum

Synonym(s): H. capsulatum

Contributor(s): Melissa Kennedy




  • Dimorphic fungus.

Active Forms

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Clinical Effects



  • Free-living dimorphic fungus.
  • Prefers neutral to alkaline soil with nitrogen enrichment, in areas with annual rainfall of 35-50 in.
  • Found in topsoil, especially in the presence of bird and bat feces.
  • Birds are passive carriers.
  • Bats undergo intestinal infections.


  • Free-living form consists of septate hyphae producing microconidia and macroconidia, (asexual reproductive units).
  • Becomes a yeast in animal hosts or suitable culture → reproduces by budding.
  • A sexual state, Ajellomyces capsulatus, has been described.


  • Inhalation, possibly ingestion and occasionally wound infection.

Pathological effects

  • Disseminated disease in humans and dogs is found in association with immunosuppression.
  • Thoracic lymph nodes become enlarged and lungs may contain nodules.
  • May disseminate to skin, mucous membranes, abdomen, central nervous system and bone marrow, also intestines.
  • Dogs: chronic intractable cough , diarrhea Diarrhea: chronic , emaciation and pyrexia. Unresponsive to antibiotics.
  • Cats: emaciation, pyrexia, dyspnea, ocular lesions.

Other Host Effects

  • Found in the top soil of endemic areas, particularly in the presence of bird and bat guano.
  • Birds are mainly passive carriers.
  • Bats undergo intestinal infection.
  • Subclinical infections are common in dogs, cats and humans.


Control via chemotherapies


  • Not available.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Kowalewich N, Hawkins E C, Skowronek A J et al (1993) Identification of Histoplasma capsulatum organisms in the pleural and peritoneal effusions of a dog. JAVMA 202 (3), 423-426 PubMed.
  • Meadows R L, MacWilliams P S, Dzata G et al (1992) Diagnosis of histoplasmosis in a dog by cytologic examination of CSF. Vet Clin Pathol 21 (4), 122-125 PubMed.
  • Davies S F & Colbert R L (1990) Concurrent human and canine histoplasmosis from cutting decayed wood. Annals of Intern Med 113 (3), 252-253 PubMed.
  • Clinkenbeard K D, Wolf A M, Cowell R L et al (1989) Canine disseminated histoplasmosis. Comp Cont Ed Pract Vet 11 (11), 1347-1351, 1354-1360 VetMedResource.