Collaborative Research: Linking environmental challenges to the likelihood and severity of epidemics: A view through the shifting window of susceptibility

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This research will help biologists who manage wildlife populations better understand the environmental conditions that make disease outbreaks more likely to catch hold and spread. A fundamental goal in biology is understanding how the environment affects human and wildlife health. Stressful environments, for instance, can make animals more susceptible to infection. But it is difficult to predict or manage the effects of stress on disease outbreaks because there are many complex, interacting processes. In addition, individuals may not respond the same way to stress. This research project will test whether chronic stress weakens the immune system during key times in an animal's development termed 'critical windows' of susceptibility. It will test whether animals are more easily infected, better at spreading the infection, and more likely to die. These results will then be used to test whether environmental stressors make disease outbreaks more likely and severe for whole populations. This work will help prioritize actions to prevent or lessen disease outbreaks. It will also provide a more sophisticated framework for studying animal diseases. In addition, the researchers will develop new teaching modules and workshops to help inform state, federal, and academic scientists, land managers, teachers, and college students about the ways in which stress affects disease outcomes. The projects will use a ranavirus, an often-lethal pathogen of amphibians, and their wood frog tadpole hosts as model system to test three specific hypotheses: environmental stressors 1) increase the average susceptibility of hosts, 2) change the timing and duration of critical windows of susceptibility, and 3) magnify initially small differences in susceptibility among hosts. A series of dose-response experiments will characterize the windows and distribution of susceptibility (both resistance to and tolerance of ranavirus infections) and determine how they are affected by high salinity and elevated temperature - two relevant and increasingly important environmental challenges. Second, laboratory experiments will characterize how these stressors affect ranavirus transmission. It is hypothesized that the most susceptible tadpoles will also be most infectious. Third, the specific physiological and immunological responses will be measured in the most and least susceptible individuals to better understand the mechanisms underlying these responses. Fourth, a sophisticated mathematical model will be used to translate these results to population-level outcomes. Lastly, experimental epidemics in semi-natural populations will be used to test the model's predictions of how stressors alter critical windows of susceptibility to affect the likelihood and severity of ranavirus epidemics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.