ISSN 2398-2977      

Histoplasma spp





  • Genus:Histoplasma.
  • Sexual stage:Ajellomyces spp.


  • Gk:histos- tissue;plasma- mold, image, formation.

Active Forms

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Clinical Effects



  • Free-living dimorphic fungus.
  • Prefers neutral to alkaline soil with neutrogen enrichment in areas with annual rainfall of 35-50 in (85-125 cm).
  • Found in topsoil, especially in the presence of bird and bat feces.
  • Birds are passive carriers, whereas 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 capsultatus, has been described.


H. capsulatum
  • Inhalation, possibly ingestion and occasionally wound infection.
    H. farciminosum
  • Arthropods may be vectors.
  • Infection via skin wounds.
  • Occasionally respiratory, gastrointestinal or conjunctival routes.

Pathological effects

H. capsulatum
  • Disseminated disease in humans and dogs is found in association with immunosuppression.
  • Recovery and resistance require cell-mediated immunity.
  • Recovered animals are immune.
    H. farciminosum
  • Skin sensitivity follows exposure.
  • Circulating antibodies can be demonstrated following infection.
H. capsulatum
  • Thoracic lymph nodes become enlarged and lungs may contain nodules.
  • May disseminate to skin, mucous membranes, abdomen, central nervous system and bone marrow.
  • Dogs present with chronic intractable cough, diarrhea, emaciation + pyrexia unresponsive to antibiotics.
  • Cats: emaciation, pyrexia, dyspnea, ocular lesions.
  • Occasionally infects horses, usually subclinically.
    H. farciminosum
  • The cause of equine epizootic lymphangitis (pseudoglanders) .
  • Local skin nodule   →   ulcerated arrows may recur.
  • Local lymphatic nodules   →   discharging sinus tracts.
  • Some cases show hematogenous spread   →   visceral organs.
  • Lesions progress from suppurative   →   granulomatous.

Other Host Effects

H. capsulatum
  • 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; occasionally seen in horses.
    H. farciminosum
  • May colonize the gastrointestinal tract.


Control via animal

  • Treatment of equine histoplasmosis rarely attempted.
  • Euthanasia   Euthanasia  advised in non-endemic areas.

Control via chemotherapies

Canine and feline histoplasmosis


  • Not available.


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Johnstone P F, Reams R, Jakovljevic S et al (1995) Disseminated histoplasmosis in a horse. Can Vet J 36 (11), 707-709 PubMed.
  • Goetz T E & Coffman J R (1984) Ulcerative colitis and protein-losing enteropathy associated with intestinal salmonellosis and histoplasmosis in a horse. Equine Vet J 16 (5), 439-441 PubMed.

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field

 Security code