ISSN 2398-2950      

Histoplasma capsulatum

ffelis
Contributor(s):

Melissa Kennedy

Synonym(s): H. capsulatum


Introduction

Classification

Taxonomy

  • Dimorphic fungus.

Active Forms

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Clinical Effects

Epidemiology

Habitat

  • Free-living dimorphic fungus.
  • Prefers neutral to alkaline soil with neutrogen 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, whereas bats undergo intestinal infections.

Lifecycle

  • 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.

Transmission

  • 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 present with chronic intractable cough, diarrhea, 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

Control via chemotherapies

Vaccination

  • Not available.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Dixon D M, Casadevall A, Klein B et al (1998) Development of vaccines and their use in the prevention of fungal infections. Med Mycol 36 (Suppl 1), 57-67 PubMed.
  • Vanden Bossche H, Dromer F, Improvisi I et al (1998) Antifungal drug resistance in pathogenic fungi. Med Mycol 36 (Suppl 1), 119-128 PubMed.

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