Abstract
Ranaviruses are responsible for mass die offs of wood frog (Lithobates sylvaticus) tadpoles. What happens in between epidemics is less clear, but juvenile (metamorphosed) stages are hypothesized to move Ranaviruses among wetlands and introduce or reintroduce these viruses into wetlands, initiating new outbreaks. A key question is under what circumstances can juvenile L. sylvaticus infect susceptible conspecifics. We examined Ranavirus transmission between juvenile L. sylvaticus in two settings: First, we measured transmission from a Ranavirus-infected frog to a co-housed susceptible frog via direct contact over a range of exposure periods. Second, we measured indirect transmission to susceptible frogs from a contaminated environment after a range of waiting times (i.e., from when the infected frog was removed to when the susceptible frog was exposed to the environment). We present evidence that juvenile frogs directly transmitted Ranavirus to susceptible frogs in all exposure periods (99.2% infected), with as little as one hour of co-housing resulting in 95.8% of susceptibles infected. Indirectly, 96.8% of susceptible frogs became infected after as long as 48-hour waiting times. Neither exposure period nor wait times influenced the probability of infection, because these probabilities are already high. In our linear regression models, viral load was best predicted by exposure period and cohort for the direct contact experiment, while wait time and the paired infective frog viral load best predicted viral load for the indirect contact experiment. Collectively, our results suggest that Ranavirus transmission readily occurs between recently metamorphosed wood frogs and via terrestrial environmental exposure.