Species distribution models predict the geographic expansion of an enzootic amphibian pathogen

Globally, numerous amphibian species have declined due to the introduction of the chytrid fungus Batrachochytrium dendrobatidis (Bd). However, the understanding of the spatiotemporal dynamics remains incomplete. Therefore, estimating the current geographic distribution of Bd is urgently needed, especially in countries like Costa Rica, where susceptible species are still recovering from Bd‐driven declines. We conducted model tuning and spatial analysis to compare the habitat suitability for epizootic and enzootic Bd in Costa Rica and to identify data‐deficient regions, opportunistic sampling, and Bd hotspots. Our dataset combined two methods of detection (histology and PCR methods) for a total of 451 Bd‐positive records from 34 localities. We found that the distribution of enzootic Bd in Costa Rica increased 60% since previous estimates in the early 2000s and extended to highlands and dry lowlands that were considered unsuitable for Bd. We also found that Bd is common across protected lands (80%) and within the herpetological provinces containing the highest amphibian richness and endemism in Costa Rica. Opportunistic sampling of Bd has focused on sites where epizootics occurred with the strongest intensity, leading to deficient or absent sampling across the Talamanca Range, the Nicoya Peninsula, and the northern lowlands. Our results showed that PCR increased the power of Bd detection in lowlands and favored the identification of Bd hotspots across the Caribbean side of Costa Rica. Our results add to the understanding of disease spread during enzootics and can be used to identify new hotspots for disease to mitigate future outbreaks of this pathogen. Abstract in Spanish is available with online material