Scientists from NSW Department of Primary Industries have identified a virus which threatened to wipe out the only existing population of a critically endangered native species of freshwater turtle – the Bellinger River snapping turtle.
NSW DPI virologist, Peter Kirkland, said positive identification of the novel nidovirus could help protect these turtles.
“What we now call the Bellinger River virus was discovered following the deaths of more than 400 turtles in 2015,” Dr Kirkland said.
“It’s a great concern as the viability of the severely reduced wild turtle population is under an extreme threat.”
Working with the NSW Office of Environment and Heritage and the Taronga Conservation Society of Australia, who conducted a field survey, collected samples and confirmed an infectious agent was present, NSW DPI was able to identify the virus.
Staff at NSW DPI’s Elizabeth Macarthur Agricultural Institute employed complex scientific procedures to isolate the virus in cell culture from a range of turtle tissues.
DNA sequencing, known as nucleic acid sequencing, was then used to identify the complete genome of the virus.
Dr Kirkland said the DNA analysis showed the Bellinger River virus was different from all other recognised nidoviruses.
“The closest related nidoviruses were recently detected in the lungs of pythons and lizards, in contrast the turtles’ kidneys were most affected,” he said.
“Once we knew we were dealing with a novel virus, NSW DPI staff quickly developed a new test, polymerase chain reaction assay (PCR), to examine additional tissue and confirm the presence of the virus.
“Electron microscopy and other tests revealed high concentrations of virus in affected tissues which indicated the virus caused the turtle deaths.”
The PCR assay is helping monitor a quarantined colony of virus-free adult turtles and their offspring at Taronga Zoo as part of a reintroduction strategy and in regular river surveys to test other species of turtles, which may also be under threat from the Bellinger River virus.
A paper detailing identification of the virus was recently published and is available online, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0205209
Abstract of the paper
In mid-February 2015, a large number of deaths were observed in the sole extant population of an endangered species of freshwater snapping turtle, Myuchelys georgesi, in a coastal river in New South Wales, Australia. Mortalities continued for approximately 7 weeks and affected mostly adult animals. More than 400 dead or dying animals were observed and population surveys conducted after the outbreak had ceased indicated that only a very small proportion of the population had survived, severely threatening the viability of the wild population. At necropsy, animals were in poor body condition, had bilateral swollen eyelids and some animals had tan foci on the skin of the ventral thighs. Histological examination revealed peri-orbital, splenic and nephric inflammation and necrosis. A virus was isolated in cell culture from a range of tissues. Nucleic acid sequencing of the virus isolate has identified the entire genome and indicates that this is a novel nidovirus that has a low level of nucleotide similarity to recognised nidoviruses. Its closest relatives are nidoviruses that have recently been described in pythons and lizards, usually in association with respiratory disease. In contrast, in the affected turtles, the most significant pathological changes were in the kidneys. Real time PCR assays developed to detect this virus demonstrated very high virus loads in affected tissues. In situhybridisation studies confirmed the presence of viral nucleic acid in tissues in association with pathological changes. Collectively these data suggest that this virus is the likely cause of the mortalities that now threaten the survival of this species. Bellinger River Virus is the name proposed for this new virus.