Jet-Setting Koalas Spread Cryptococcus gattii VGII in Australia

Abstract

Cryptococcus gattii molecular type VGII is one of the etiologic agents of cryptococcosis, a systemic mycosis affecting a wide range of host species. Koalas (Phascolarctos cinereus) exhibit a comparatively high prevalence of cryptococcosis (clinical and subclinical) and nasal colonization, particularly in captivity. In Australia, disease associated with C. gattii VGII is typically confined to Western Australia and the Northern Territory (with sporadic cases reported in eastern Australia), occupying an enigmatic ecologic niche. A cluster of cryptococcosis in captive koalas in eastern Australia (five confirmed cases, a further two suspected), caused predominantly by C. gattii VGII, was investigated by surveying for subclinical disease, culturing koala nasal swabs and environmental samples, and genotyping cryptococcal isolates. URA5 restriction fragment length polymorphism analysis, multilocus sequence typing (MLST), and whole-genome sequencing (WGS) provided supportive evidence that the transfer of koalas from Western Australia and subsequently between several facilities in Queensland spread VGII into uncontaminated environments and environments in which C. gattii VGI was endemic. MLST identified VGII isolates as predominantly sequence type 7, while WGS further confirmed a limited genomic diversity and revealed a basal relationship with isolates from Western Australia. We hypothesize that this represents a founder effect following the introduction of a koala from Western Australia. Our findings suggest a possible competitive advantage for C. gattii VGII over VGI in the context of this captive koala environment. The ability of koalas to seed C. gattii VGII into new environments has implications for the management of captive populations and movements of koalas between zoos. IMPORTANCE Cryptococcus gattii molecular type VGII is one of the causes of cryptococcosis, a severe fungal disease that is acquired from the environment and affects many host species (including humans and koalas). In Australia, disease caused by C. gattii VGII is largely confined to western and central northern parts of the country, with sporadic cases reported in eastern Australia. We investigated an unusual case cluster of cryptococcosis, caused predominantly by C. gattii VGII, in a group of captive koalas in eastern Australia. This research identified that the movements of koalas between wildlife parks, including an initial transfer of a koala from Western Australia, introduced and subsequently spread C. gattii VGII in this captive environment. The spread of this pathogen by koalas could also impact other species, and these findings are significant in the implications they have for the management of koala transfers and captive environments.

Abdominal cryptococcosis in dogs and cats: 38 cases (2000‐2018)

“…2011, Schmertmann et al . 2019). Similarly, disproportionately large number of abdominal cryptococcosis in the current study where observed in patients domiciled in Perth, Western Australia compared to the Eastern states and South Australia suggesting that the alimentary tract might be more likely to be the primary portal of entry for such biotypes.…”

“…Detailed information regarding treatment and outcome was not provided in either of these studies. Previously California and Western Australia have been noted to have a high overall prevalence of C. gattii VGII and VGIII (Byrnes 3rd et al 2011) associated with climatic conditions, soil types, and the diversity of eucalyptus (WA only) and other native trees (McGill et al 2008, Carriconde et al 2011, Schmertmann et al 2019. Similarly, disproportionately large number of abdominal cryptococcosis in the current study where observed in patients domiciled in Perth, Western Australia compared to the Eastern states and South Australia suggesting that the alimentary tract might be more likely to be the primary portal of entry for such biotypes.…”

Consensus guidelines for the diagnosis and management of cryptococcosis and rare yeast infections in the haematology/oncology setting, 2021

“…42 Key Australian papers on C. gattii infection include a comprehensive review by Chen et al, 6 insights derived from a nationwide retrospective study of culture-confirmed C. gattii from 2000 to 2007 14,25 and work emphasising its zoonotic aspects. 43,44 There has been no prospective treatment study focused on C. gattii infection to date and no new data have emerged to guide therapy of C. gattii infection since the previous 2014 guidelines. Locally, clinicians typically use a prolonged induction phase with amphotericin B and 5-flucytosine for 4-6 weeks followed by consolidation therapy for 12-18 months, for treatment of CNS cryptococcosis.…”

On the Emergence of Cryptococcus gattii in the Pacific Northwest: Ballast Tanks, Tsunamis, and Black Swans

“…One final note: Western Australia is the region of the continent most prone to tsunamis (55), and it is becoming apparent that at least some populations of Australian C. gattii originated in the western region (i.e., Perth) and have been anthropogenically transported via infected animals (i.e., koalas) to other parts of the continent (56). A tsunami-borne mechanism of transport from ocean to land in Western Australia is highly speculative but certainly possible if the coastal waters were previously contaminated.…”