Chronic wasting disease in the central Appalachian region of the United States

Open Access
Evans, Tyler Scott
Graduate Program:
Wildlife and Fisheries Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
October 17, 2014
Committee Members:
  • William David Walter, Thesis Advisor
  • chronic wasting disease
  • CWD
  • Northeast
  • Odocoileus virginianus
  • white-tailed deer
Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy that was first detected in white-tailed deer (Odocoileus virginianus) in the northeastern United States (Northeast) in 2005. Maintaining a healthy population of white-tailed deer is important to states in the Northeast for numerous recreational and economic reasons. The Midwest documented a decline in hunter participation and hunter-associated revenue following detection of CWD, and the presence of CWD in the Northeast could have a similar impact on local economies and wildlife management efforts. Considering CWD is a new and emerging disease in the Northeast, I investigated sampling strategies by state, ecology of deer, and environmental drivers of disease to better understand CWD in the region. I surveyed 14 state agencies responsible for CWD surveillance in the Northeast to identify how surveillance efforts have changed following detection of CWD in the region. Annual surveillance efforts throughout the region initially exceeded 15,000 deer per year. Loss of federal funding in 2012, however, led to a drastic reduction in these efforts (<9,000 deer per year), with Pennsylvania alone accounting for ~4,000 samples. This reduction in sampling requires states to allocate resources into areas that are at greatest risk for CWD to maximize efficiency of these limited resources. Literature pertaining to state responses to CWD had been nonexistent for the Northeast and these surveys were the initial effort for collaboration between adjacent states that had detected CWD. I compiled data that have been shown to influence movements of deer and epidemiology of CWD in other regions. This was particularly important because all previous analyses had been performed in regions with landscapes that were dominated by agriculture or rangeland in contrast to the predominantly forested landscape of the Northeast. Spatial processes, including spread of disease, rely on the scale of deer movement (e.g., home range), and this scale can be related to landscape. Therefore, I estimated size of home range in relation to landscape for 45 white-tailed deer in Pennsylvania to identify the spatial scale that described movements and home range of deer in the region. I documented that size of home range was related to connectivity of forest, with contiguous forest associated with expansive size of home range. In areas with high levels of fragmentation or less contiguous forest, home ranges were small (e.g., 0.63 km2 for females) likely because deer were able to fulfill daily requirements for forage intake over a smaller area. Differences in size of home range by landscape likely would result in differences in the distribution of disease due to increased contact rates among matriarchal groups of deer that occupy these fragmented landscapes. Conversely, deer that occupy expansive tracts of contiguous forest may establish home ranges of larger size (e.g., 2.65 km2 for females) due to foraging and breeding requirements and also may introduce disease into new areas. These concepts suggest that surveillance in highly fragmented areas should be concentrated locally to reflect less expansive home ranges that may inhibit expansive spread of disease, whereas surveillance in contiguously forested areas should be applied to a broad scale to reflect expansive home ranges that may allow disease to spread into new areas. To further understand these concepts, I incorporated landscape into my analysis of CWD by linking location-based surveillance data to environmental and spatial factors that could influence the distribution of CWD in Maryland, Virginia, and West Virginia. I identified a clustering of CWD in an area where forested habitat was sparse and open (e.g., agricultural) and developed (e.g., suburban) habitats were more prominent. I identified areas of elevated risk that included a potential corridor east of the study area where spread of CWD may be expedited among several states. This corridor was at elevated risk because it was dominated by an anthropogenic landscape where forests were even less prominent than in the core of the study area where CWD was most prevalent. These open and developed landscapes may promote contact between deer, and proactively sampling these areas may improve feasibility of containment efforts if CWD is detected. Since my research concluded, a free-ranging white-tailed deer tested positive for CWD in this corridor in 2013 so state agencies should consider collaborating to further monitor spread of CWD in this corridor and other high-risk landscapes.