COLLABORATIVE RESEARCH: Evolution of virulence in a host-pathogen system

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This project will improve our understanding of the evolution of infectious disease systems while also contributing to education and the development of conservation strategies for protecting amphibian diversity. Disease epidemics rarely end in the complete extinction of host populations. Especially in highly lethal diseases, theory predicts a shift away from the outbreak phase to a post-outbreak stage where hosts and pathogens persist in a shared environment. Such transitions in disease states present a moving target that limits the development of successful intervention strategies. This research investigates the factors that drive evolutionary shifts in disease dynamics by focusing on one of the most devastating infectious diseases of vertebrates in recorded history, amphibian chytridiomycosis. Chytridiomycosis is caused by a fungal pathogen that can spread rapidly through amphibian populations and cause extremely high levels of mortality, suggesting that it is a strong agent of natural selection. This disease has caused - and continues to cause - dramatic losses of amphibian biodiversity around the world. The investigators are using an in-depth understanding of chytridiomycosis to develop science-based conservation strategies. The research is integrated with educational outreach, including public workshops and presentations centered on the annual International Save the Frogs Day. This research capitalizes on a decade of research in Central America and on an unprecedented archive of disease data, pathogen isolates, and host samples. Pathogen isolates and host samples were collected and archived during the outbreak phase of the disease and similar data are being collected during the endemic phase, beginning eight to ten years later. The researchers are using experimental and molecular methods to investigate the hypotheses that (1) the level of pathogen virulence has shifted since the original outbreaks and (2) that hosts have evolved to be more tolerant of infection. To test these hypotheses, the investigators are testing the historic and contemporary samples to identify phenotypic and genetic differences linked to pathogen virulence host immune defenses. The results will provide insights for safeguarding amphibian biodiversity and for understanding the role of evolution in shaping post-epidemic dynamics of emerging infectious diseases.