Human disturbance and higher temperatures are linked to amphibian chytrid fungus in Catalonia, Northeastern Spain

Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), threatens amphibian biodiversity worldwide. While Bd is widespread in Europe, its local epidemiology remains poorly understood. We conducted a five-year survey (2019–2023) of 3,253 amphibians from 14 species across 41 sites in Catalonia, Northeastern Spain, to assess chytrid occurrence and environmental drivers. Using duplex qPCR, Bd was detected in 141 individuals (4.3%) from seven species, while Bsal was absent. Infections were geographically widespread but varied among species: Alytes obstetricans larvae showed the highest prevalence (26.6%), indicating a potential reservoir role, and Hyla meridionalis also exhibited high prevalence (14.3%) and infection loads, suggesting Bd tolerance. Other species, including urodeles and some alpine taxa, showed low or no infection. Although no overt disease was observed, chytridiomycosis-related mortality was suspected in A. obstetricans. Binomial GLMMs identified anthropogenic disturbance and maximum summer temperature as significant predictors of Bd occurrence. The apparent endemicity of Bd and absence of Bsal reinforce the need for continued surveillance, an improved understanding of host roles in disease dynamics, and integration of key environmental drivers to inform mitigation measures and preserve amphibian biodiversity.