Cryptococcosis and the ecology of cryptococcus neoformans.

Abstract

Cryptococcosis is a cosmopolitan infectious disease of humans and animals caused by an encapsulated basidiomycetous yeast-like fungus Cryptococcus neoformans. Clinical manifestations range from asymptomatic carriage in the respiratory tract to chronic pulmonary disease to meningitic disease with dissemination to the skin and other sites also reported. The incidence of infections varies with geographic location and with patient groups; AIDS has now become the most common predisposing factor for infection. Cryptococcal virulence factors include the ability to form a polysaccharide capsule, produce melanin and to grow at 37°C. C. neoformans var. neoformans (serotypes A and D) has a world-wide distribution and been isolated from various sources in nature and is noted for its association with accumulations of avian guano, especially with pigeon excreta. C. neoformans var. gattii (serotypes B and C) has a more restricted global distribution corresponding to a subtropical to tropical climate. Environmental isolations have now established that C. neoformans var. gattii serotype B appears to have a specific ecological association with Eucalyptus camaldulensis and Eucalyptus tereticornis. The global distribution of these two trees appears to correspond to the epidemiologic distribution of cryptococcosis caused by C. neoformans var. gattii. The epidemiology of cryptococcosis can primarily be explained by exposure to an infective aerosolized inoculum, such as basidiospores released from specific host plants and/or desiccated blastoconidia (yeast cells) disseminated from accumulations of dried pigeon dung. The ecology of C. neoformans still remains largely unresolved, studies on the host-parasite interaction between serotype B and E. camaldulensis are still in progress, and extensive environmental searches are now underway to determine the natural habitats of serotypes A, C and D. © 1994, The Japanese Society for Medical Mycology. All rights reserved.