Identification of a novel nidovirus as a potential cause of large scale mortalities in the endangered Bellinger River snapping turtle (Myuchelys georgesi)

Abstract

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 situ hybridisation 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.

On a razor's edge: Status and prospects of the critically endangered Bellinger River snapping turtle, Myuchelys georgesi

“…The average body condition of diseased M. georgesi retrieved during the outbreak was significantly lower than that of the healthy M. georgesi removed for the first insurance population, in keeping with reports of diseased turtles being in poor condition or emaciated (Moloney et al, ; Zhang et al, ). However, the condition of the diseased turtles was more variable, with several being in better condition than expected.…”

“…It is also unknown how the disease was able to progress upstream at a rate of more than 1 km per day. It seems unlikely that infected turtles would travel upstream at this rate, but no other virus vectors have been confirmed (Zhang et al, ).…”

“…In 2015, a novel nidovirus of unknown origin, now named Bellinger River virus (BRV), was apparently responsible for mass mortality of Bellinger River snapping turtles ( Myuchelys georgesi ) in the Bellinger River, New South Wales (NSW), Australia (Jakob‐Hoff et al, ; Moloney, Britton, & Matthews, ; Zhang et al, ). Myuchelys georgesi (Figure a) is a moderate‐sized, omnivorous, short‐necked chelid turtle (maximum carapace length 240 mm) with an historical distribution confined to approximately 70 km of the Bellinger River and a short length of its major tributary the Kalang River (Allanson & Georges, ; Blamires, Spencer, King, & Thompson, ; Cann, ; Cann, Spencer, Welsh, & Georges, ).…”

“…External disease symptoms of affected turtles (Figure b) included lethargy, emaciation, conjunctivitis, anterior uveitis, nasal discharge, hind‐limb paresis, and plaque‐like skin lesions. Histopathology revealed inflammation of the eyes, oral cavity, and internal organs, including the spleen, kidneys, and liver (Moloney et al, ; Zhang et al, ). Diseased turtles were initially given veterinary care, but this failed to prevent death, and severely ill turtles were thereafter euthanized.…”

“…The disease was not observed in any other species, including the Macquarie turtle ( Emydura macquarii ; Figure c), which also inhabits the Bellinger and Kalang rivers. However, low levels of BRV RNA were detected in swabs from two E. macquarii sampled in November 2015 (Zhang et al, ). Although BRV appears to have been the principal aetiological agent, confirmation of its lethality to M. georgesi through experimental transmission studies has not been possible because M. georgesi is Critically Endangered (Zhang et al, ).…”