High prevalence of subclinical frog virus 3 infection in freshwater turtles of Ontario, Canada.

Ranaviruses have been associated with chelonian mortality. In Canada, the first two cases of ranavirus were detected in turtles in 2018 in Ontario, although a subsequent survey of its prevalence failed to detect additional positive cases. To confirm the prevalence of ranavirus in turtles in Ontario, we used a more sensitive method to investigate if lower level persistent infection was present in the population. Here we report results via a combination of qPCR, PCR, Sanger sequencing and genome sequencing from turtles from across Ontario, with no clinical signs of illness. We found 2 positives with high viral load and 5 positives with low viral load. Histopathology found subtle histological changes. DNA sequences identified two types of frog virus 3 (FV3), and genome sequencing identified a ranavirus similar to wild-type FV3. Our results show that the virus has been present in Ontario's turtles as subclinical infections.