Histoplasma capsulatum

Shmuel Shoham, M.D., John G. Bartlett, M.D.
Histoplasma capsulatum is a topic covered in the Johns Hopkins ABX Guide.

To view the entire topic, please or purchase a subscription.

Official website of the Johns Hopkins Antibiotic (ABX), HIV, Diabetes, and Psychiatry Guides, powered by Unbound Medicine. Johns Hopkins Guide App for iOS, iPhone, iPad, and Android included. Explore these free sample topics:

Johns Hopkins Guides

-- The first section of this topic is shown below --


  • Two varieties of Histoplasma capsulatum relevant to human infections: this module will focus on var. capsulatum, which will be referred to as H. capsulatum.
    • H. capsulatum var. capsulatum: nearly worldwide distribution
    • H. capsulatum var. duboisii: mostly restricted to western Africa
  • Geographic distribution: H. capsulatum is found in multiple locations across the globe.
    • Important endemic areas in North and Central America include (but are not limited to) the Ohio and Mississippi River valleys, the Caribbean basin, and Mexico.
    • Fungus can also be found in parts of South America, Asia, and Africa.
    • Important to note that microfoci of endemicity exist both within and outside of areas traditionally associated with the fungus.
  • Fungus grows in soil, particularly if enriched by bird or bat guano (e.g. bird roosts, chicken coops, caves with bats).
  • Dimorphic growth: H. capsulatum may grow as a mold or as a yeast depending the situation.
    • Mold form predominates in the environment (or in vitro, when incubated at < 35°C).
      • Morphology as mold
        • Aerial hyphae: long tubular structures.
        • Macroconidia: thick walled spherical structures 8-15 μm in diameter with surface projections. This distinctive structure is diagnostic Fig 1.
        • Microcondia: smooth spherical structures 2-4 μm in diameter. When contaminated soil is disturbed, microconidia can become airborne and settle in patients’ alveoli to cause infection.
    • Yeast form: with infection, the fungus transitions to yeast, which is the form seen in tissues (or in vitro when incubated at temperatures of ≥37°C).
      • Appearance: oval, narrow based, budding yeast, 2-4 μm in diameter Fig 2.
      • May be seen within macrophages or in tissues and serve to facilitate dissemination from the lung to multiple other sites.

-- To view the remaining sections of this topic, please or purchase a subscription --

Last updated: February 26, 2017