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Jessica Agius, Threatened Species Recovery Hub & The University of Sydney
Infectious diseases are an increasing threat to wildlife populations worldwide, and have been associated with species declines and extinctions, particularly on islands. In 2014, a novel Enterococcus bacterium was discovered in the captive breeding population of Lister’s geckos (Lepidodactylus listeri) and blue-tailed skinks (Cryptoblepharus egeriae) on Christmas Island and resulted in the deaths of over 50 individuals.
This outbreak prompted a more in-depth health analysis of Christmas Island reptiles, which was undertaken by Threatened Species Recovery Hub PhD candidate Jessica Agius, from The University of Sydney. The assessment additionally discovered two papillomaviruses and several parasites in both invasive and endemic geckos.
The bacterium
The Enterococcus bacterium results in inevitable death of infected animals. Screening has revealed that introduced geckos on the Cocos (Keeling) islands, the site of the recent skink introduction, are not affected. Antibiotics have been trialled on Asian house geckos on Christmas Island to see whether Parks Australia could treat infected animals, and while some promising results were achieved, those results also suggested the bacterium may be highly resistant to antibiotics. This disease therefore threatens the conservation management of the Critically Endangered reptiles on Christmas Island, and poses a high biosecurity risk.
The viruses
The discovery of two novel papillomaviruses in Christmas Island lizards is the first report of papillomavirus in lizards globally. The papillomavirus and Enterococcus bacterium occurred in some animals at the same time, meaning they may work together to cause disease. A diagnostics test to detect the viruses in apparently healthy animals has been developed, and continuing research is seeking to unravel the effects of these viruses on Christmas Island lizards.
The parasites
During the health assessment several internal and external parasites were found: mites, tapeworms, lungworms, roundworms, flukes and coccidia. Infestation by parasites can cause damage to the reptiles’ internal organs, increasing their susceptibility to disease and, in some cases, cause death.
Reptiles from the Cocos islands and Christmas Island are equally affected by parasites, so understanding them will be valuable to managing populations on both Christmas Island and the Cocos islands.
What’s next for Christmas Island reptiles?
The reintroduction of blue-tailed skinks into a Christmas Island exclosure has been successful to date, and continued monitoring will help us to evaluate longer-term success. Although initial results are promising for the translocation of skinks to Pulu Blan, more monitoring is needed to assess the longer-term fate of that trial.
The disease research will now attempt to understand more about the genome of the Enterococcus bacterium, its resistance to antibiotics, and the most effective antibiotic treatments.
We will also continue our investigation into the impact of introduced species on the Lister’s gecko and blue-tailed skink, which stand as fascinating examples of millions of years of reptile evolution in the isolation of Christmas Island.
This Threatened Species Recovery Hub project is a collaboration between Parks Australia (Christmas Island National Park), the University of Western Australia, Charles Darwin University, The University of Sydney, Taronga Conservation Society Australia, the Australian Registry of Wildlife Health Taronga Zoo and the Holsworth Wildlife Research Endowment, with input and advice from the Christmas Island Reptile Advisory Panel (a committee of Parks Australia staff and independent experts). The project is supported by the Australian Government’s National Environmental Science Program.