Cryptococcus

Genus of imperfect yeasts (basidiomycetes), which form round and oval shoot cells (shoot fungi) with a capsule-like coating of polysaccharide mucus. Of the genus Cryptococcus, practically only C. neoformans is pathogenic and appears as the causative agent of cryptococcosis. Filobasidella neoformans is the name for the sexual form of C. gatii.

Cryptococcus neoformans is divided into two varieties, which differ in their growth behaviour in culture (grows on Sabouraud agar at 30-37 °C):

• Cryptococcus neoformans var. grubii (serotype A), Cryptococcus neoformans (seroytp D), hybrids of both varieties (serotype AD) are distributed worldwide and are responsible for at least 80-90% of all cryptococci in HIV infection.
• Cryptococcus neoformans var. gattii (serotypes B and C) is distributed almost exclusively in the tropics or subtropics and is responsible for cryptococcoses in immunocompetent hosts
• Interspecies hybrids that are becoming increasingly differentiated (Cuomo CA et al. 2018)

In the soil and in organic materials. The concentration is particularly high in bird, especially pigeon dung. C. neoformans var. gatti is also very often found in the vicinity and on eucalyptus plants and their remains. C.gatti can also infect otherwise healthy people.

Infection in humans occurs via inhalation of the heat and desiccation resistant pathogens. Injury mycoses are also described (although rarely). A transmission from person to person can almost be ruled out as a path of infection. Domestic and wild animals, especially cats, and other vertebrates can also become ill with cryptococcosis. A transmission from animals to humans is not known so far.

Cryptococcoses belong to the AIDS-defining diseases. Cryptococcoses are less frequent in people after organ transplants, in malignant tumours, in immunosuppressive therapy, in other chronic diseases such as diabetes mellitus and sarcoidosis. Only rarely are people without underlying diseases affected (May RC et al. 2015).

incubation period: probably up to several months

The primary stage of the infection (see below cryptococcosis) is often clinically inapparent, but can also manifest clinically as pneumonia and in some cases be chronically progressive. With hematogenic dissemination, the pathogen can enter all parenchymatous organs, CNS, eyes, bones, skin and joints can also be affected.

Fungal cells: 2.5-10 μm large, no formation of pseudophyphae and hyphae. Direct microscopic detection is particularly important for the rapid differentiation of meningoencephalitis. For this purpose an ink preparation according to Burri is prepared from the liquor sediment.

The pathogen can be easily visualised in the tissue by means of Grocott staining (silvering).

Rapid diagnosis by antigen test (glucucrono-xylo-mannan) from cerebrospinal fluid, urine and serum samples.

PCR diagnostics

Culture possible without problems. Duration 3-5 days. For differentiation from other pathogens, special agar according to Neger seed (colonies grow dark due to their pigment content).

1. Cuomo CA et al (2018) Advances in Cryptococcus genomics: insights into the evolution of pathogenesis. Mem Inst Oswaldo Cruz 113:e170473.
2. May RC et al (2015) Cryptococcus: from environmental saprophyte to global pathogen. Nat Rev Microbiol 14:106-117.
3. Samarasinghe H et al (2018) Hybrids and hybridization in the Cryptococcus neoformans and Cryptococcus gattii species complexes. Infect Genet Evol 66:245-255.