Cryptococcus

Cryptococcus (literally "hidden sphere") is a genus of fungus. Species grow in culture as yeasts. The perfect (sexual) forms or teleomorphs of Cryptococcus species are filamentous fungi in the genus Filobasidiella. The name Cryptococcus is used when referring to the imperfect forms (yeast states) of the fungi.

Cryptococcus neoformans is the most prominent medically important species. It is best known for causing a severe form of meningitis and meningo-encephalitis in people with HIV/AIDS. There are about 37 recognized species of Cryptococcus, but the taxonomy of the group is currently being re-evaluated with up-to-date methods. The majority of species live in the soil and are not harmful to humans. Very common species include Cryptococcus laurentii and Cryptococcus albidus. Of all species, Cryptococcus neoformans is the major human and animal pathogen. However, Cryptococcus laurentii and Cryptococcus albidus have been known to occasionally cause moderate-to-severe disease in human patients with compromised immunity (owing to HIV infection, cancer chemotherapy, metabolic immunosuppression, et cetera).

Cryptococcus gattii (formerly Cryptococcus neoformans var gattii) is endemic to tropical parts of the continent of Africa and Australia. It is capable of causing disease (cryptococcosis) in non-immunocompromised people. It has been isolated from eucalyptus trees in Australia. Since 1999, there has been an outbreak of Cryptococcus gattii infections in eastern Vancouver Island, an area not generally thought to be endemic for this organism. Cases have since been described in the Pacific Northwest, in both Canada and the United States.

The cells of these species are covered in a thin layer of glycoprotein capsular material that has a gelatin-like consistency and that, among other functions, serves to help extract nutrients from the soil. But C. neoformans capsule is different in being richer in glucuronic acid and mannose, having O-acetyl groups, and functioning as the major virulence factor in cryptococcal infection and disease.