Ranavirus-Positive Hatchling Eastern Box Turtles (Terrapene carolina carolina) Suggest Vertical Transmission without Observed Disease.

Ranaviruses (Iridoviridae) are highly virulent emerging pathogens that affect a wide range of ectotherms, including fishes, amphibians, and reptiles. In turtles, ranaviruses have contributed to deadly epizootic events in wild and captive populations. Despite ranaviruses being pathogens of major concern, their transmission is poorly understood in reptiles and the potential for vertical transmission (from mother to offspring) remains unaddressed. We investigated vertical transmission of ranavirus in eastern box turtles (Terrapene carolina carolina) by screening 25 reproductive females and their offspring (n=74). We collected samples from adult females up to four times during the 2022 reproductive season and, in some cases, for up to 3 yr prior. We collected samples from offspring at hatch in 2022 and approximately 8 mo later. We documented seven reproductive females with positive ranavirus detections, although no females tested positive at more than one time point and all detections occurred 2-3 yr before reproductive monitoring in 2022. We documented nine hatchlings from six clutches with positive ranavirus detections, seven of which were produced by four females without a documented history of ranavirus detection. None of the ranavirus-positive hatchlings exhibited clinical signs of disease throughout an 8-mo captive rearing period; five of seven initially positive hatchlings were negative at release, and all survived until release. Hatchlings in which we detected ranavirus exhibited low viral loads, and we found no evidence that they transmitted the virus to their clutchmates during captive rearing. Collectively, our results suggest that vertical transmission of ranavirus is possible in box turtles, but we found no evidence that the low viral loads we observed resulted in disease. Further research is needed to determine the precise mode of vertical transmission in turtles and to understand the potential individual and population-level effects of maternally derived infections.