Fusarium species cause a broad spectrum of infections in humans including superficial infections, such as keratitis and onychomycosis, as well as locally invasive and disseminated infections; invasive and disseminated infections occur almost exclusively in severely immunocompromised patients . Fusarium species may also cause allergic diseases, such as sinusitis in immunocompetent individuals , and mycotoxicosis following ingestion of food contaminated by toxin-producing Fusarium species . Fusarium species are also important plant pathogens that cause various diseases on cereal grains  and occasionally cause infection in animals .
The mycology, pathogenesis, and epidemiology of fusariosis will be reviewed here. The clinical manifestations, diagnosis, treatment, and prevention of fusariosis are discussed separately. (See "Clinical manifestations and diagnosis of Fusarium infection" and "Treatment and prevention of Fusarium infection".)
Fusarium species are widely distributed in soil, subterranean and aerial plant parts, plant debris, and other organic matter . They are also present in water worldwide .
Growth in vitro — Fusarium species grow rapidly on many media that do not contain cycloheximide, which inhibits its growth. On potato dextrose agar, Fusarium species produce white-, lavender-, pink-, salmon-, or gray-colored colonies with velvety or cottony surfaces .
Microscopic appearance — Microscopically, the hyphae of Fusarium in tissue resemble those of Aspergillus species, with septate hyaline hyphae 3 to 8 microns in diameter that typically branch at acute angles (picture 1 and picture 2). Adventitious sporulation, which is the ability to sporulate in tissue and blood, may be present ; the identification of hyphal and yeast-like structures in the same specimen is highly suggestive of fusariosis in high-risk patients.