Histoplasma

Histoplasma is a genus of dimorphic fungi commonly found in bird and bat fecal material.[1] Histoplasma contains a few species, including—Histoplasma capsulatum—the causative agent of histoplasmosis;[2] and Histoplasma capsulatum var. farciminosum (old term, Histoplasma farciminosum), causing epizootic lymphangitis in horses.[3]

Histoplasma
Histoplasma (bright red, small, circular). PAS diastase stain
Scientific classification
Kingdom:
Fungi
Division:
Ascomycota
Class:
Ascomycetes
Order:
Onygenales
Family:
Ajellomycetaceae
Genus:
Histoplasma

Darling (1906)
Type species
Histoplasma capsulatum
Darling (1906)
Species

Histoplasma capsulatum
Histoplasma duboisii

This fungus is mainly found in the Ohio and Mississippi River Valleys in the United States as well as Central/South America, Africa, Asia and Australia.[4]

Forms / Stages

Histoplasma capsulatum has two forms: its environmental form is hyphae with microconidia and tuberculate macroconidia while its tissue form is a small intracellular yeast with a narrow neck and no bud with no capsule[5] and can be detected in aerobic blood culture bottle.[6] In the saprophytic stage, it bears features of both microconidia and macroconidia. Infection occurs through inhalation of the small microconidia or small mycelia fragments. The dimorphic mold-yeast transforms and enters host macrophages and proliferates within them most often seen in immunodeficient individuals.[7]

References
  1. Giannella RA (1996). Salmonella. In: Baron's Medical Microbiology (Baron S et al, eds.) (4th ed.). Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1.
  2. Ryan KJ; Ray CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
  3. OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2004 Chapter 2.5.13, "Archived copy". Archived from the original on 2007-08-04. Retrieved 2007-06-14.CS1 maint: archived copy as title (link)
  4. "Histoplasmosis". Centers for Disease Control and Prevention. 28 October 2020. Retrieved 27 January 2021.
  5. Hutton, JP (April 1985). "Hyphal forms of Histoplasma capsulatum. A common manifestation of intravascular infections". Archives of Pathology and Laboratory Medicine. 109: 330–332 – via Pubmed.
  6. Salimnia, Hossein (August 2021). "Hyphal and yeast forms of Histoplasma capsulatum growing within 5 days in an automated bacterial blood culture system". Journal of Clinical Microbiology. 50: 2833–2834 – via Pubmed.
  7. Lopez, CE (Oct 2006). "Dimorphism and Pathogenesis of Histoplasma capsulatum". Revista Argentina de Microbiologia. 38: 235–242 – via Pubmed.


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