Jet-Setting Koalas Spread Cryptococcus gattii VGII in Australia

Area of Science:

• Veterinary Mycology
• Wildlife Epidemiology
• Genomic Epidemiology

Background:

• Cryptococcus gattii molecular type VGII is an emerging cause of cryptococcosis in diverse hosts.
• Koalas, particularly in captivity, show high rates of cryptococcosis and nasal colonization.
• C. gattii VGII is geographically restricted in Australia, primarily to Western Australia and the Northern Territory.

Purpose of the Study:

• To investigate a cluster of cryptococcosis in captive koalas in eastern Australia.
• To determine the source and spread of Cryptococcus gattii VGII within this koala population.
• To assess the implications for captive koala management and pathogen transmission.

Main Methods:

• Surveyed for subclinical disease in captive koalas.
• Cultured koala nasal swabs and environmental samples for C. gattii.
• Genotyped C. gattii isolates using URA5 RFLP, MLST, and whole-genome sequencing (WGS).

Main Results:

• Identified a cluster of cryptococcosis predominantly caused by C. gattii VGII in captive koalas.
• Genotyping confirmed koala transfers from Western Australia introduced and spread VGII to new environments.
• MLST identified isolates as predominantly sequence type 7, with limited genomic diversity and basal relationship to Western Australian strains.
• Evidence suggests a potential competitive advantage of C. gattii VGII over VGI in this captive setting.

Conclusions:

• Koala movements, including an initial introduction from Western Australia, were responsible for spreading C. gattii VGII in eastern Australia.
• This study highlights the potential for koalas to introduce and disseminate C. gattii VGII into naive environments.
• Findings have significant implications for managing koala populations and inter-facility movements to prevent pathogen spread.