MONITORING RANAVIRUS-ASSOCIATED MORTALITY IN A DUTCH HEATHLAND IN THE AFTERMATH OF A RANAVIRUS DISEASE OUTBREAK.

The ranaviruses are an emerging group of viruses that infect amphibians, fish, and reptiles. Although ranaviruses have not been linked to extinctions, emergence in amphibian communities has resulted in population declines for some species. We present the results of ranavirus-associated mortality in a Dutch national park in the aftermath of an outbreak associated with a common midwife toad virus (CMTV)-like ranavirus. We monitored five bodies of water across Dwingelderveld National Park, the Netherlands, in 2011-13. Dead and live amphibians were counted weekly July-September and every 2 wk in June and October. Dead amphibians were collected and tested for ranavirus infection. In addition, we measured biologic, chemical, and physical site characteristics to test for a correlation with ranavirus-associated mortality. Ranavirus infection was widespread in our study area and we observed nearly continuous presence of dead, ranavirus-infected amphibians in the presence of asymptomatic, live amphibians throughout our study. Fatalities occurred in larval, subadult, and adult amphibians. Ranavirus infection prevalence (based on fatal cases) was significantly associated with increasing fractions of adults and subadults compared to juveniles and larvae in the population, but was unrelated to any other measured site characteristics. Our findings showed that a CMTV-like ranavirus can persist long term in an ecosystem, affecting a diversity of amphibian species and life stages for a prolonged period. This study illustrates the importance of monitoring the modes of spread for ranaviruses and their impact on amphibian populations.