9th International Deer Biology Congress

AUTHORS: Jonathan D. Cook, Sonja A. Christensen, David M. Williams, William F. Porter – Boone and Crockett Quantitative Wildlife Center, Michigan State University

ABSTRACT: Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy that affects at least seven North American cervid species, including white-tailed deer [1, 2]. Since its discovery in Colorado in 1967, CWD has become a serious threat to the sustainable future of susceptible host species because of long-term population declines in deer herds where the disease is well established. To prevent disease establishment, wildlife managers need information regarding the current state of disease to make rapid assessments and implement aggressive management actions. However, their decisions are almost always made with limited information regarding the local extent of CWD in an area. In this study, our objective was to leverage research findings from Wisconsin [3], a state where CWD is established, to make predictions on the spatial extent of CWD in Michigan, a state where CWD has recently emerged. The model utilizes partial differential equations to generate forecasts regarding where CWD may spread and grow in prevalence. Factors affecting spread and prevalence include sex and age of susceptible animals and landscape features in close proximity to disease detections. To assess the model fit for Michigan, we performed repeated simulations across a range of times and points of disease origin and evaluated results based on their ability to predict spread to known locations of disease. Our results provide a potential origin site in western Michigan that occurred prior to the first-free ranging detection in the state. The results also indicate that CWD will spread and grow most quickly in locations of high forest density, such as the Huron-Manistee National Forest, a nearly one-million acre forest immediately north of areas known to hold CWD-affected deer. Based on these findings, we generate a spatially-explicit map that provides the estimated probability of infection for each 1-square mile unit across the entire study area. Utilizing model extrapolation and validation is critical to the prevention of CWD establishment because these approaches can leverage information from a few disease detections to provide managers with insight into where and when CWD may occur next.