From Brisbane's Roma Street Parkland to the outer suburbs of Perth, a contagious fungal disease is quietly spreading through Australia's wild reptile populations, and researchers say the speed and reach of its advance is alarming. The pathogen at the centre of the concern is Nannizziopsis barbatae, commonly known among reptile keepers as "Yellow Fungus Disease," and according to the Sydney Morning Herald, scientists now believe it poses a risk to roughly half of Australia's reptile species.
The disease first showed up in captive bearded dragons around 2009. It remained confined to captivity until 2013, when two free-living eastern water dragons from locations separated by 30 kilometres across Brisbane were identified with proliferative dermatitis, necrosis, ulceration and emaciation. Since then, the picture has grown considerably more worrying. Affected lizards have been identified in Western Australia, Victoria, New South Wales and Queensland, with focal outbreaks in Brisbane parklands.
The cause of the outbreak is a fungal pathogen that feeds on keratin, the main protein in skin. Infection causes severe skin lesions and can progress to systemic infection. In practice, that means the disease is rarely survivable. Dermatomycoses caused by Nannizziopsis species are slowly progressive and often fatal. Skin lesions progress over several months from dry and yellow to hyperkeratotic plaques to exudative and necrotic ulcers. In the most severe cases, infection extends to muscle, bone and internal tissues including liver, heart, kidney, lungs and intestine.
The scale of the potential threat comes into sharper relief when considered against Australia's extraordinary reptile diversity. Australia has over 860 species of reptiles, a large number in comparison to other continents; North America's total is about 280. Of these, 93 per cent are unique to the continent. That concentration of endemic species makes Australia particularly vulnerable to any pathogen with a broad host range, and this one qualifies. First known to the reptile pet trade as a primary pathogen causing untreatable severe dermatomycosis, since 2013 the fungus has emerged in a growing number of phylogenetically and ecologically distant free-living reptiles across Australia. Research demonstrates the pathogen's virulence-related genomic features, within-population spread, and survival costs, all of which imply it could pose a threat to Australian reptiles in the future.
Researchers at the Wildlife Health Australia network have been tracking the pathogen's spread, noting confirmed cases across multiple states and calling for anyone who suspects the disease in captive or wild animals to notify researchers immediately. A key concern is that no dedicated national surveillance programme currently exists. There are currently no targeted surveillance programmes for reptile fungal diseases. The absence of systematic monitoring means case numbers likely understate the real extent of infection.
It is worth asking whether the disease could have originated, at least partly, in the reptile pet trade. The pathogen has been detected in agamids, monitor lizards, skinks and freshwater turtles across Queensland, New South Wales and Western Australia. Many of the animals documented with this infection are pets, and researchers do not yet know whether the novel infection has originated in the pet trade or not. That uncertainty points to a gap in biosecurity oversight: the legal trade in exotic and native reptiles creates pathways for pathogens to jump between captive and wild populations, and the regulatory frameworks governing that trade have not kept pace with the emerging fungal disease threat.
Some conservationists urge caution about worst-case projections. Scientists acknowledge that the natural ecology of Nannizziopsis species remains largely unknown, and it is possible the fungus has long been present in Australian ecosystems at low levels, only now becoming more visible due to improved diagnostic tools. The pathogen may have been introduced to wild lizards through spillover, or may be an endemic fungus only recently detected or emerging among wild lizards due to altered host susceptibility or changing environmental conditions. Climate variability, which affects the immune function of ectothermic animals, may be contributing to increased susceptibility, but that link has not yet been definitively established.
On one point researchers are clear: the fungus does not appear to threaten humans. Research has shown that Nannizziopsis barbatae was not able to grow at human body temperature, largely mitigating concerns that the fungus could pose a threat to humans. Still, only trained individuals using appropriate biosafety measures should handle reptiles with suspicious skin lesions.
A 2025 study published in the Australian Veterinary Journal, drawing on cases from the Australia Zoo Wildlife Hospital, documented ten fresh cases of onygenalean dermatomycoses in five free-ranging native squamate species between 2023 and 2024, suggesting the disease is continuing to expand rather than stabilising. Herpetofauna populations are declining globally due to multiple threatening processes including disease. Ectothermic animals have proven particularly vulnerable to fungal diseases, and such diseases have accounted for up to 65 per cent of pathogen-driven animal extinction events.
The honest policy question is one of resource allocation. Monitoring and researching emerging wildlife pathogens is unglamorous work that competes for funding against more visible conservation priorities. But the precedent set by chytridiomycosis, the amphibian fungal disease that has contributed to the collapse of frog populations worldwide, shows that acting early is far cheaper than responding to catastrophic population declines. For a country that hosts one of the world's most biodiverse reptile collections, establishing a funded, coordinated surveillance programme for reptile fungal disease is a straightforward investment in protecting an irreplaceable natural asset. The Department of Climate Change, Energy, the Environment and Water has the mechanisms to act; the case for doing so is strong.