Skin-nontumor / Clinical dermatology
Infectious disorders
Fungi - Histoplasma capsulatum

Author: Ha Kirsten Do, M.D. (see Authors page)

Revised: 24 May 2016, last major update September 2010

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Fungi - Histoplasma capsulatum

Cite this page: Fungi - Histoplasma capsulatum. website. Accessed June 20th, 2018.
Definition / general
  • Infection is caused by inhalation of airborne spores of Histoplasma capsulatum, a dimorphic saprophytic fungus found in soil contaminated with bird or bat feces
  • Highest incidence is in North America, particularly in the central states along the Mississippi River basin
  • Histoplasma is endemic to Southeast US (80% of this population may have positive intradermal histoplasmin skin test), Mexico, Africa, Asia
  • Transmission of disease is by inhalation of spores that can be found in feces of bats, starlings (type of bird) and chickens; causes a primary pulmonary pneumonia
Clinical features
  • There are several clinical manifestations of histoplasmosis:
    • Acute pulmonary histoplasmosis: almost 90% patients have no symptoms
    • Chronic pulmonary histoplasmosis: occurs mostly in patients with underlying lung disease
    • Progressive disseminated histoplasmosis: occurs mostly in immunosuppressed patients
    • Ocular histoplasmosis syndrome: eye disease, occurs in 1 - 10% of the patients
    • Cutaneous histoplasmosis: erythema nodosum or erythema multiforme

  • Pneumonia is self-limited in immunocompetent patients, but disseminates in immunocompromised (very young, very old, HIV+) to liver, spleen, bone marrow, nodes, lung, rarely to skin
  • Disseminated disease: strongly associated with AIDS; patients have fever, weight loss, splenomegaly; variable cutaneous lesions
  • Cutaneous lesions are nodules, papules, ulcers; less commonly macules, pustules or vesicles
  • Culture shows tan-white-brown wooly mold at 25 - 30 C on Sabouraud dextrose agar
  • Organisms have delicate, septate hyphae, 1 - 2 microns thick, with large rough-walled macroconidia 5 - 15 microns
  • Reverts to yeast at 37 C on sheep blood agar
  • Yeast is 2 - 4 microns, budding, single nuclei, round/oval with thin rigid walls
Case reports
  • Most with minimal disease require no treatment
  • Moderate to severe cases require antifungal drugs, usually Itraconazole x 9 months in immunocompetent patients, Itraconzazole followed by IV amphotericin B in immunosuppressed patients
Clinical images

Images hosted on PathOut servers:

Breast skin, HIV+, courtesy of Dr. Mark R. Wick

Microscopic (histologic) description
  • Isolated intracellular organisms and large aggregates surrounded by chronic inflammatory cells and fibroblasts (but no neutrophils or eosinophils); also epithelioid granulomas with variable caseation
  • May be narrow based budding of spores
Microscopic (histologic) images

Images hosted on PathOut servers:

Breast skin, courtesy of Dr. Mark R. Wick

Images hosted on other servers:

GMS, Lacto-phenol cotton blue

2 - 3 mm hyperpigmented papules and dermal basophilic spherules 2 - 4 microns

Slide culture with small microconidia and tuberculate macroconidia

Within macrophages

Positive stains
Molecular / cytogenetics description
  • PCR probes are now available
  • Best diagnostic test is the urinary ELISA
Differential diagnosis
Additional references