Evidence for low prevalence of ranaviruses in Ontario, Canada’s freshwater turtle population

Abstract

Background Ontario, Canada is home to eight native species of turtles; all eight are federally listed as Species At Risk, due to anthropogenic threats. However, until recently, reports of infectious disease have been lacking. Ranavirus is seen as an emerging threat for ectotherms globally, with mass die-offs most often reported in amphibians. Ranavirus has been detected in Ontario’s amphibian populations, can be transmitted via water, and can be transmitted from amphibians to turtles. However, no studies on the prevalence of this virus in Ontario’s turtles have previously been carried out. With recent reports of two confirmed positive case of ranavirus in turtles in Ontario, a knowledge of the ecology of ranavirus in Ontario’s turtles has become even more important. This study estimates the prevalence of ranavirus in Ontario’s turtles, and investigates the hypothesis that this is a newly emergent disease. Methods Sixty-three samples were tested for ranavirus via PCR. These included a variety of turtle species, across their home range in Southern Ontario. Fifty-two of the samples originated from the liver and kidney of turtles who had succumbed to traumatic injuries after being admitted to the Ontario Turtle Conservation Centre; ten of the samples were taken from cloacal swabs, lesion swabs, or tail clips collected from live turtles showing signs of clinical disease. One of the live turtles was later euthanized for humane reasons and PCR was also carried out on the liver/kidney. Results None of the 63 samples were found to be positive for ranavirus via PCR. The zero prevalence found in this study translates into a population prevalence estimate of less than 5%, with no change in prevalence from 2014–2018. Discussion This is the first report on the prevalence of ranavirus in Ontario’s turtles, and will help build an understanding of the ecology of this virus in Ontario. Ranavirus has historically been underreported in reptiles, but there has been an increase in global reports recently, most likely due to increased awareness. A carrier state is thought to exist in reptiles which makes surveillance in the population via random sampling a viable method of detection of prevalence. The first report of ranavirus in Ontario turtles occurred in 2018. This study suggests a continued low population prevalence for the years 2014–2018, however. Ongoing surveillance is necessary, as well as investigation of the eDNA presence in waterways as compared to the PCR of resident turtles, to further understand the sensitivity of these species to ranavirus infection. The utilization of qPCR would be helpful, to better quantify any positives encountered.

Comparative Genomics Analysis between frog Virus 3-like Ranavirus from the First Canadian Reptile Mortality Event and Similar Viruses from Amphibians

“…Ministry of Agriculture, Food and Fisheries 23 . A second ranavirus case from Ontario was identi ed in 2018 after a wood turtle (Glyptemys insculpta) also tested positive by PCR 32 . DNA samples from infected liver tissue from two snapping turtles part of the original cluster and virus ampli ed in cell culture were provided to the Genomics Unit at the Canadian Food Inspection Agency's National Centre for Foreign Animal Disease, Winnipeg, Manitoba, for characterization by whole genome sequencing.…”

Trace Amounts of Ranavirus Detected in Common Musk Turtles (Sternotherus odoratus) at a Site Where the Pathogen Was Previously Common

“…Because our research period was limited to summers (in this and previous studies), we have not explored seasonal variation in ranavirus prevalence in our study site. Opportunistic samples from other studies or efforts, such as wildlife rehabilitation centers, provide an important opportunity to survey ranavirus using a nondestructive approach that minimizes stress to animals [ 37 ]; however, detection power may be limited when the virus has waned in an ecosystem and samples are limited within species and seasons. We find it noteworthy that we did not detect any ranavirus DNA in 105 tissue samples from 81 individuals of C. p. picta collected between 2021 and 2022, where it was commonly found (prevalence 23.8%) and, therefore, easily detected among a sample of only 42 individuals in 2010 [ 27 ].…”

Health Assessment of Wild Northern Diamond-Backed Terrapins (Malaclemys Terrapin Terrapin) in New Jersey, Usa

“…There is also concern that the wildlife trade is playing a role in the movement of pathogens to new areas, as seen with the introduction of chytridiomycosis from African clawed frogs ( Xenopus laevis ; Karesh et al 2005). Several pathogens are recognized as having the potential to negatively affect wild turtle populations, including Mycoplasmopsis spp., ranaviruses, and herpesviruses (Ossiboff, Raphael, Ammazzalorso, Seimon, Newton et al 2015; Ossiboff, Raphael, Ammazzalorso, Seimon, Niederriter et al 2015; Carstairs 2019), but it is unknown what impacts these diseases may have on northern diamond-backed terrapins.…”