Assessing mitigation options for an emerging fungal pathogen threatening European and Palearctic salamander diversity

Abstract

Emerging wildlife diseases represent both a major driver of global biodiversity loss and one of the greatest challenges to conservation science. In spite of the recognized extent and magnitude of disease-driven declines worldwide, and of the considerable research targeting them, successful mitigation remains elusive. The amphibian chytrid fungus Batrachochytrium salamandrivorans (Bsal) causes lethal chytridiomycosis in several palearctic salamander species. This pathogen, believed to have recently entered Europe from its native range in Asia, has already driven the rapid collapse of populations of fire salamanders (Salamandra salamandra) in the Low Countries and threatens to cause massive biodiversity loss in Europe and North America. Development of mitigation actions is urgently advocated; here, we formally assess the potential for mitigation success using epidemiological models. First, we use an integral projection model to explore the impact of Bsal in a population of a highly vulnerable host species (fire salamander S. salamandra), and to evaluate potential mitigation actions. Available evidence suggests that a Bsal outbreak in a fire salamander population will lead to its rapid extirpation. Treatments (antifungals or probiotics) would need to effectively interrupt transmission (reduce probability of infection by nearly 90%) to reduce the risk of host extirpation and successfully eradicate Bsal. Improving survival of infected hosts is likely to be detrimental as it increases the potential for pathogen transmission and spread. Only the active removal of most of the host population has some potential to locally eradicate Bsal and interrupt its spread. However, even this extreme possibility is challenged by the presence of additional host species. Using a multiple-host compartmental model, we show that co-occurring alpine newts act as a Bsal reservoir towards salamanders; their ability to clear infection results in a greater pool of infected individuals (particularly given the lack of acquired immunity), accelerating and sustaining the outbreak in salamanders. substantial removal (>95%) of both species would be needed to avoid an outbreak at the community level; to maximize salamander persistence, with strong between-host transmission newts would need to be entirely removed from the system, making even this extreme action unlikely to even prove feasible. In summary, mitigation of Bsal outbreaks in susceptible host species is highly challenging, requiring effective interruption of transmission and radical removal of host individuals. The ability of Bsal to infect multiple hosts further reduces management options. More generally, to explore and assess management options we recommend a focus shift from single species to the community level. To develop practical management actions, epidemiological models can be most effective if embedded directly in the management decision context, rather than adapted to it a posteriori.