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Rapid spread of a virulent amphibian pathogen in nature


Considering that emerging infectious diseases are one of the major drivers of global amphibian decline, controlling the spread of infections are even more challenging. Amphibian skin disease chytridiomycosis, which is caused by two species of fungi belonging to the Batrachochytrium genus, has been detected in at least 700 amphibian species causing mass mortalities in all continents where amphibians occur. Most Alytes species, including the Betic midwife toad (A. dickhilleni), are highly susceptible to B. dendrobatidis (Bd) with lethal consequences. The presence of Bd infection in A. dickhilleni was confirmed ten years ago in just three localities across the entire distribution range of this threatened species. Here we report the extraordinary Bd expansion through the entire distribution range of A. dickhilleni and analyse if former infected populations acted as the source of transmission events to current infected populations. Currently, Bd infection is broadly distributed across the entire distribution range of the species and the increase of infection prevalence reached 30–50% during a decade. The populations where the infection was detected a decade ago could be identified as likely sources of infection for some locations where the pathogen is now present. The introduction of infected amphibian hosts into previously naïve A. dickhilleni breeding sites, and other anthropogenic processes, are seeming to be the most plausible way of Bd range expansion, motivating mass mortalities, population declines and extirpation events of this threatened amphibian species.

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Funding for this study was provided by the Consejería de Agricultura, Ganadería, Pesca y Desarrollo Sostenible of Junta de Andalucía. Special thanks to Jesús del Río, coordinator of the conservation program of endangered amphibians of Andalusia. We also thank Ester Cerezo-Valverde for field assistance, Cristina Sausor for laboratory assistance and Trenton WJ Garner for providing insightful and detailed comments on earlier versions of the paper.


This work was funded by the Consejería de Medio Ambiente of Junta de Andalucía (Contract Number NET378406/1).

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Authors and Affiliations



JB and EGM conceived the ideas and designed methodology. EGM, BT, and JB collected the samples. BT performed DNA extraction and qPCR analyses. SCF conducted geographic profiling analysis. JB and BT ran the statistical analyses. BT, SCF, and JB wrote the first draft; all authors contributed to revisions.

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Correspondence to Jaime Bosch.

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Field work was carried out under permission of Consejería de Medio Ambiente of Junta de Andalucía, Castilla La Mancha and Región de Murcia.

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Thumsová, B., González-Miras, E., Faulkner, S.C. et al. Rapid spread of a virulent amphibian pathogen in nature. Biol Invasions 23, 3151–3160 (2021).

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  • Batrachochytridium dendrobatidis
  • Chytridiomycosis
  • Betic midwife toad
  • Alytes dickhilleni
  • Geographic profiling