Infection and co-infection by the amphibian chytrid fungus and ranavirus in wild Costa Rican frogs.

Amphibian populations are globally threatened by emerging infectious diseases, and 2 pathogens in particular are recognized as major threats: the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) and ranaviruses. Here, we evaluated the prevalence of infection by Bd and ranavirus in an assemblage of frogs from a lowland wet forest in Costa Rica. We found an overall prevalence of 21.3% for Bd and 16.6% for ranavirus, and detected both pathogens widely among our 20 sampled species. We found a positive association between ranavirus and Bd infection in one of our 4 most commonly sampled species. We also found a positive but non-significant association between infection by ranavirus and infection by Bd among species overall. Our study is among the first detailed evaluations of ranavirus prevalence in the American tropics, and to our knowledge is the first to detect a positive association between Bd and ranavirus in any species. Considerable research attention has focused on the ecology of Bd in tropical regions, yet we argue that greater research focus is necessary to understand the ecology and conservation impact of ranaviruses on amphibian populations already decimated by the emergence of Bd.