sampling, coupled with detailed molecular typing of isolates, revealed areas of permanent and transient colonization with primarily three genotypes of the fungus. C. gattii was found in air, soil, water, and in association with numerous tree species. Importantly, there is solid evidence for human-mediated dispersal of the pathogen, and C. gattii has now been detected in the environment on the mainland of British Columbia and in the Pacific Northwest. Associated animal and human cases are now being reported and further spread of the pathogen may be inevitable.
The basidiomycetous yeast Cryptococcus neoformans has a global distribution and has achieved prominence in recent decades because of its propensity to infect immunocompromised people (Casadevall and Perfect, 1998). In fact, cryptococcosis is recognized as an AIDS-defining illness, and in the absence of highly active antiretroviral therapy, the disease is a significant cause of death in individuals with HIV infection (Bicanic and Harrison, 2005; Bicanic et al., 2005). People and animals acquire the fungus via the inhalation of desiccated yeast cells or basidiospores from environmental sources such as avian guano, soil, and trees. Pulmonary infection often results in dissemination to the central nervous system and C. neoformans is the leading cause of fungal meningitis (Casadevall and Perfect, 1998).
Isolates of C. neoformans have previously been divided into three varieties known as grubii, neoformans, and gattii and into serotypes (A–D and hybrids such as AD) defined by antigenic differences in the capsular polysaccharide that is the major virulence factor (Casadevall and Perfect, 1998). The gattii variety is now recognized as a separate species based on phenotypic and molecular traits, and mating (Kwon-Chung et al., 2002). Thus the current view is that the species C. neoformans (var grubii and neoformans) contains strains of serotypes A, D, and AD, and the distinct species C. gattii contains isolates of the B and C serotypes (Kwon-Chung and Varma, 2006). An excellent review of the differences between C. gattii and C. neoformans has been published by Sorrell (Sorrell, 2001).
Extensive surveys have been performed over the past 10 years to characterize the genotypes and distribution of C. neoformans and C. gattii isolates (Barreto de Oliveira et al., 2004; Boekhout et al., 2001; Boukhout et al., 1997; Fraser et al., 2005+; Kidd, 2003; Kidd et al., 2004 ++; Kidd et al., 2005+; Meyer et al., 1999; Meyer et al., 2003). These surveys used a variety of DNA-based typing methods to provide detailed classifications of isolates into molecular types. Thus, isolates of C. neoformans var grubii (serotype A) are represented by the VNI, VNII, and VNB (Litvintseva et al., 2006) molecular types, var neoformans (serotype D) is represented by the VNIV type, and isolates of the AD hybrid serotype are the VNIII type. Four molecular types are recognized for C. gattii isolates (designated VGI–VGIV) and further divisions within the molecular types have been identified