Cryptococcus neoformans in the koala (Phascolarctos cinereus): colonization by C. n. var. gattii and investigation of environmental sources


Faculty of Veterinary Science, The University of Sydney, NSW 2006, Australia


This study is the one in a series looking at the relationship among Cryptococcus neoformans var. gattii, koalas and the environment. The koala was used as a natural biological sampler in an attempt to understand the dynamics of C. neoformans var. gattii in Australian environments. Evidence of asymptomatic nasal and skin colonization for extended periods by large numbers of C. n. var. gattii was obtained and geographical factors assessed. The key finding was the ability of koalas to amplify numbers of C. n. var. gattii in certain environments. Koalas were not found to be obligatory for the survival of the organism in all environments. Geographical factors alone could not explain differing rates of nasal and skin colonization in koalasindifferentenvironments.Astrongassociationbetweenhealthykoalasand C. n. var. gattii was confirmed and C. n. var. gattii was isolated from novel sources, including the turpentine gum tree (Syncarpia glomulifera), tallow wood (Eucalyptus microcorys) and flooded gum (E. grandis). It seems likely that as yet undiscovered environmental sources of C. n. var. gattii exist in eastern Australia. Further investigation of host, environmental and organism factors integral to the host pathogen relationship will assist an understanding of the progression from colonization to tissue invasion and cryptococcosis in all species.