''Histoplasma'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of dimorphic

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

commonly found in bird and bat fecal material. ''Histoplasma'' contains a few species, including—''

Histoplasma capsulatum ''Histoplasma capsulatum'' is a species of dimorphic fungus. Its sexual form is called ''Ajellomyces capsulatus''. It can cause pulmonary and disseminated histoplasmosis. ''H. capsulatum'' is "distributed worldwide, except in Antarctica, but m ...

''—the causative agent of

histoplasmosis Histoplasmosis is a fungal infection caused by ''Histoplasma capsulatum''. Symptoms of this infection vary greatly, but the disease affects primarily the lungs. Occasionally, other organs are affected; called disseminated histoplasmosis, it can ...

; and ''Histoplasma capsulatum var. farciminosum'' (old term, ''Histoplasma farciminosum''), causing epizootic lymphangitis in horses. 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.

Forms / Stages

Histoplasma capsulatum has two forms: its environmental form is

hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

with microconidia and tuberculate macroconidia while its tissue form is a small intracellular yeast with a narrow neck and no bud with no capsule and can be detected in aerobic

blood culture A blood culture is a medical laboratory test used to detect bacteria or fungi in a person's blood. Under normal conditions, the blood does not contain microorganisms: their presence can indicate a bloodstream infection such as bacteremia or f ...

bottle. 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 Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...

and proliferates within them most often seen in

immunodeficient Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...

individuals.

References

External links

''Histoplasma'' information
from doctorfungus.org Onygenales Eurotiomycetes genera Taxa described in 1906 {{Ascomycetes-stub