Clarifying the links between climate and host-pathogen interactions will provide valuable insights into the dynamics, ecology and evolution of infectious diseases and provide direction for effective management of threatened populations. Chytridiomycosis, a disease caused by Batrachochytrium fungi, has recently caused declines and extinctions of amphibian populations on several continents. The central objective of this project was to develop predictive models of chytridiomycosis, based on a clear understanding of how climate impacts the ecology and dynamics of this host-pathogen interaction, and use these models to investigate the potential of alternative disease management tactics.

The technical approach included (Objective I) field surveys to investigate how climate impacts the ecology of chytridiomycosis, (Objective II) field and lab experiments to assess the impacts of current and future climates on amphibian-Batrachochytrium dynamics, and (Objective III) the development of data-driven mechanistic models to evaluate how climate affects the host pathogen interaction. The models will permit the project team to work with wildlife management personnel to address (1) where and when outbreaks of chytridiomycosis are likely to threaten amphibians on Department of Defense (DoD) installations and (2) the effectiveness of alternative management strategies for sustaining threatened amphibian populations through times of increased disease risk.

The project team detected Batrachochytrium dendrobatidis (Bd) at all the field sites and in nearly every amphibian species sampled but B. salamandrivorans (Bsal) was not detected. The project team found strong patterns of seasonality in Bd prevalence and load in amphibians as well as seasonal variation in these animals’ defenses against Bd. The Bd detected on field-captured amphibians is strikingly diverse and belongs to two sub lineages of the global pandemic lineage (Bd-GPL). The experimental results suggest that Bd may be able to adapt to new climates and that developing as larvae under climate stress can impair a host’s ability to defend itself against Bd. The modeling efforts suggest that management actions should focus on identifying reservoir host species and reducing Bd persistence in aquatic habitats. The models also suggest that efforts aimed at reducing the potential of particular host species to act as pathogen reservoirs, and specifically efforts that cause the stochastic extinction of Bd from an aquatic breeding habitat, may be an effective way to prevent outbreaks of chytridiomycosis on DoD lands as the climate changes.

Benefits of this work to the DoD include a clearer understanding of (1) the geographic, genetic, and host distribution of the Bd and Bsal pathogens, (2) drivers of seasonal disease dynamics, and (3) impacts of climate change on disease-relevant host-and pathogen physiology in the chytridiomycosis system. The models that have been developed will also aid in determining which hosts are potential reservoirs for Batrachochytrium pathogens and where, when, and how management actions can be taken to reduce Bd persistence and chytridiomycosis risk for threatened and endangered amphibian species. Given the potential impact of climate change on disease, studies of this nature will be critical in developing strategies to promote the long-term health of threatened amphibians and other wildlife on DoD lands.