A collaborative project undertaken by Jessica Agius in association with Taronga Conservation Society Australia and The University of Sydney, and supervised by Drs David Phalen, Karrie Rose and Hannah Bender
Remote Christmas Island was once considered a biodiversity hotspot, supporting a diverse array of endemic species. In the years following human settlement, multiple extinction events have occurred and the island ecosystem has been devastated by significant biodiversity loss. Widespread habitat destruction and fragmentation, and invasive species introductions have historically contributed to species declines; however, the recent emergence of a novel infectious disease has now been recognised as a key threat to two reptiles endemic to Christmas Island: the critically endangered and now extinct in the wild Lister’s gecko (Lepidodactylus listeri) and blue-tailed skink (Cryptoblepharus egeriae).
Christmas Island gecko exhibiting signs consistent with infection by Enterococcus lacertideformus. Numerous swellings of the subcutaneous tissue of the head, rostrum and gingiva are evident.
PhD student Jessica Agius in the field on Christmas Island examining a Christmas Island endemic gecko for signs of disease.
Fine needle aspiration cytology collected from a subcutaneous lesion of a gecko affected by Enterococcus lacertideformus. Numerous chains of the bacteria encapsulated by the biofilm matrix are evident.
Histology showing multiple colonies of Enterococcus lacertideformus invading local tissues and replacing the normal structures of the mandible of an affected gecko.
Post-mortem liver of a gecko affected with the Enterococcus lacertideformus bacterium. Multiple nodules of bacteria are replacing the normal hepatic and gall bladder parenchyma.
Enterococcus lacertideformus is a recently discovered bacterium, originally observed in captive populations of Lister’s geckos and blue-tailed skinks on Christmas Island in October 2014. Since then, the organism has been identified in the highly invasive common house (Hemidactylus frenatus) and mute geckos (Gehyra mutilata), both widespread throughout Christmas Island. The presence of the organism within free-ranging invasive geckos complicates efforts to conserve the Lister’s gecko and blue-tailed skink.
Geckos and skinks infected with E. lacertideformus initially present with masses around the head and mouth, and markedly swollen eyes. As the disease progresses, bacteria become disseminated throughout the body, resulting in fatigue and death. When examined microscopically, skin masses are composed of large colonies of bacteria which replace and displace tissues in the head and form similar space-occupying masses in many organs. Unusually, bacterial proliferation is associated with a minimal to absent host immune response. Little is known about the origin, transmission and host susceptibility of E. lacertideformus, and the susceptibility of this bacterium to antibiotics is unknown.
Funding from the Australian and Pacific Science Foundation supported foundational research to sequence E. lacertideformus and to describe interactions between this novel bacterium, its host and the environment. By sequencing, assembling and analysing the bacterial genome we gained insight into evolutionary relationships, antimicrobial resistance genes and virulence factors that might contribute to the bacteria’s ability to cause disease in reptiles.
Next we explored the health of endangered Christmas Island reptiles using the genetic data generated by sequencing the E. lacertideformus genome. In doing so, we discovered two novel papillomaviruses, constituting the first complete papillomavirus genomes to be characterised in lizards. These datasets provided important knowledge regarding the host range, tissue distribution and evolutionary relationships of both viruses in Christmas Island reptiles. Finally, in order to understand how E. lacertideformus causes disease in susceptible reptiles, we conducted an experimental infection and treatment trial, and successfully identified candidate antibiotics for further evaluation. Following this trial, the effectiveness of one antibiotic, enrofloxacin, was further examined, and recommendations for treatment were determined.
Research funded by the Australian and Pacific Science Foundation provided critical information and treatment protocols required to effectively manage the endangered Lister’s gecko and blue-tailed skink. Results generated by this research have informed conservation management actions and contributed to efforts to conserve the health and survival of the last remaining endemic reptiles on Christmas Island.