Characterizing the epidemiology of ranavirus in North American chelonians: diagnosis, surveillance, pathogenesis, and treatment

Ranaviruses have been proposed as a major threat to amphibian biodiversity, however the impact of these pathogens on reptiles is less well understood. In this dissertation, a quantitative PCR was developed that was 100% efficient in detecting the 54 bp segment of the major capsid protein of frog virus 3 (FV3) (Genus: Ranavirus; Family: Iridoviridae). This assay was used to estimate the prevalence of ranavirus infections in 606 eastern box turtles (Terrapene carolina carolina) from several different states. The overall prevalence of ranaviruses in this study population was 1.5% (95% confidence interval: 0.8 – 2.9%), with a non-significantly higher prevalence in juveniles (3.5%; 95% CI: 0.9 – 11.9%) than adults (0.5%; 95% CI: 0.1 – 1.8%). The low prevalence found in this population supports the theory that this virus is associated with acute disease and death. Clinical signs recorded in box turtles that were significantly associated with ranavirus infection were fractures and diarrhea. In challenge studies at two separate environmental temperatures, red-eared sliders (Trachemys scripta elegans) inoculated through intramuscular injection with a FV3-like virus had higher mortality rates when maintained at 22oC than at 28oC, supporting the theory that this virus is less virulent at higher temperatures. FV3-like DNA was detected in whole blood, oral swabs, and cloacal swabs. The sensitivity and specificity of detection in whole blood samples when compared to necropsy were 100%, while sensitivity and specificity in oral and cloacal swabs were found to be 83% and 100%, respectively. Skeletal muscle from injection site and kidney had the highest viral copy number post-mortem, while tongue had the lowest. Significant histopathological changes included fibrinoid vasculitis in all tissues. Clinical signs observed in experimentally inoculated red-eared sliders included lethargy, conjunctivitis, oral plaques, oral ulcers, and injection site swelling. Hematologic changes were evaluated in both free-ranging box turtles and experimentally inoculated red-eared sliders. Red-eared sliders showed only one significant change, a reduction in total solids over time. Box turtles were non-significantly lymphopenic. Intracytoplasmic inclusions were identified in two infected red-eared sliders and one infected box turtle, but they were not consistently associated with ranavirus-status. Treatment of ranavirus with anti-viral therapy has been reported to have variably poor success, but was based on anecdotal dosing recommendations. Pharmacokinetic analysis of a single oral dose of valcyclovir demonstrated measureable levels, and may prove useful against this virus. The work presented in this dissertation provides new insight into the epidemiology of ranavirus in chelonians