is a topic covered in the Johns Hopkins ABX Guide
To view the entire topic, please sign in or purchase a subscription.
Pediatrics Central™ is an all-in-one application that puts valuable medical information, via your mobile device or the web, in the hands of clinicians treating infants, children, and adolescents. Explore these free sample topics:
-- 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 sign in or purchase a subscription --