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

SIMPLE SUMMARY: Ranaviruses are an important source of disease and mortality for reptiles, amphibians, and fishes around the world. In 2021–2022, we surveyed two species of aquatic turtles at a Virginia site where previous research found ranavirus in turtles and lizards. We used 249 samples of skin collected from turtles to determine whether they carried ranavirus using genetic testing. We found very small amounts of ranavirus DNA in 2.8% of Common Musk Turtles, which have not been previously reported to carry ranavirus. The amounts of ranavirus DNA were so small that we think they were picked up from the environment and were probably not indicative of turtles being infected with the virus. We did not find any ranavirus in Eastern Painted Turtles, which contrasts a 2010 study wherein 23.8% of turtles of this species in the same site carried ranavirus. The amount of ranavirus in our study site, as reflected in the skin samples from the turtles, appears to have dropped dramatically since previous research conducted over a decade ago. Because we only detected ranavirus in 4 out of 249 skin samples, and in only one of 2 years, we emphasize the need for large sample sizes and multiyear sampling to detect ranavirus in wild populations. ABSTRACT: Ranaviruses are global multi-host pathogens that infect ectothermic vertebrates and cause mass mortality events in some species. In 2021–2022, we surveyed two species of aquatic turtles in a Virginia site where previous research found ranavirus in lizards (Sceloporus undulatus) and turtles (Chrysemys picta picta and Terrapene carolina carolina). We sampled tissues from 206 turtles and tested 249 samples (including recaptures) for ranavirus using qPCR. We detected trace amounts of ranavirus DNA in 2.8% of Common Musk Turtles (Sternotherus odoratus). We did not detect the virus in Eastern Painted Turtles (C. p. picta). The Ct values from animals carrying ranavirus corresponded to positive controls with a concentration of one copy of ranavirus DNA per microliter and likely reflect DNA in the environment rather than ranavirus infection in turtles. Turtles carrying ranavirus DNA came from only one pond in one year. The amount of ranavirus in our study site, as indicated by tissue samples from turtles, appears to have dropped dramatically since previous research conducted over a decade ago. This study represents the first report of ranavirus detected in S. odoratus and contributes to the scarce literature on longitudinal surveys of ranavirus in wild chelonians. We emphasize the need for large sample sizes and multi-year sampling to detect this pathogen in wild populations.