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First occurrence of chytrid fungus (Batrachochytrium dendrobatidis) in toads of the genus Bombina in Croatia

Year: 2026

Type: article

Abstract: The global amphibian biodiversity crisis is significantly driven by the fungal pathogen Batrachochytrium dendrobatidis (Bd), contributing to declines in populations of hundreds of species and dozens of species extinctions over the last half-century. While the pathogen is widely distributed across at least 26 European nations, it remains undocumented in many regions of the Balkans. This study reports the first detection of Bd within populations of the genus Bombina in Croatia, based on field surveys conducted during the vernal and autumnal seasons of 2023 and 2024. Surveys targeted 19 distinct sites in Papuk Nature Park across an altitudinal gradient (87 m to 864 m), focusing on ephemeral aquatic microhabitats such as shallow temporary ponds and roadside ditches. Molecular screening of 82 individuals via quantitative PCR (qPCR) confirmed the pathogen in eight individuals across four ponds. Infections were identified in yellow-bellied toads (Bombina variegata) and their hybrids, while all sampled fire-bellied toads (B. bombina) tested negative. These results confirm the regional establishment of Bd in Croatia. Given the relative isolation of the infected locations and the low likelihood of the pet trade as a distribution factor, spread via biological vectors or natural hydrological connectivity seems likely. The presence of Bd in these isolated populations introduces a serious long-term threat to their viability, emphasizing the need for monitoring, targeted conservation, and in situ mitigation strategies to prevent sudden population collapses.

Source: Acta Herpetologica

DOI: 10.36253/a_h-20338