Data from: Is exposure to chytrid fungus and ranavirus higher in ponds invaded by American bullfrogs?

Data associated with manuscript: https://doi.org/10.1007/s10530-025-03648-8The spread of emerging infectious diseases (EIDs) and non-native invasive species are interconnected processes driving biodiversity loss. A key example involves Batrachochytrium dendrobatidis (Bd) and ranavirus (Rv), pathogens contributing to global amphibian declines. Their occurrence has been linked to invasive American bullfrogs (Lithobates catesbeianus) serving as asymptomatic vectors. To determine the relationship between Bd and Rv exposure and bullfrogs, we investigated whether pathogen occurrence and environmental loads are correlated with the presence and density of bullfrogs and whether the seasonal variation in Bd exposure is related to bullfrog phenology. We sampled 157 ponds in Belgium, including four with known bullfrog and Bd presence that were monitored monthly for two years, using quantitative environmental DNA (eDNA) barcoding. We validated a duplexed assay that simultaneously targets Bd and Rv, and we quantified eDNA concentrations of bullfrogs, Bd, and Rv serving as proxies for density and pathogen loads. Bd was detected more frequently when bullfrogs were present and both the frequency of detection and environmental loads of Bd increased in ponds with high bullfrog densities. In contrast, Rv detection likelihood and load were not significantly related to bullfrog presence or density. Seasonal fluctuations in Bd loads varied between ponds with and without breeding activity. In the former, Bd was consistently detected, likely due to overwintering tadpoles. In the latter, Bd loads varied throughout the year, with peak loads coinciding with juvenile immigration. Collectively, our findings indicate that amphibian exposure to Bd, but not Rv, is higher in areas and periods where bullfrogs are present and occur at high densities