Genetic assignment tests reveal dispersal of white-tailed deer: Implications for chronic wasting disease

Investigating sources of infection for new disease cases is critical to effective disease management. Chronic wasting disease (CWD) was first detected among white-tailed deer (Odocoileus virginianus) in Illinois in 2002. Although CWD was focused in northern Illinois, 4 infected deer were sampled in 2011 from locations greater than 100 km south of the disease focus. We used assignment tests (Geneclass2 and Oncor) to determine a likely genetic source location for infected deer. Our baseline data set consisted of 310 deer sampled from 10 locations. From the baseline data set, we determined the most likely genetic source location of 15 CWD-positive and 15 CWD-negative deer. A total of 17-20% back-assigned to their sample location as their most likely genetic source location and the remainder of the animals cross-assigned to another location. The average distance between locations was 41.4 km for Geneclass2 and 43.4 km for Oncor (range 0.0-90.8 km). Distances between source and sampling locations were similar for positive and negative animals. Distances for males were greater than those for females using Oncor, but there was no difference in distance based on age. Because there are few barriers to gene flow for white-tailed deer, managers should reduce movement of deer in CWD-infected areas in an effort to reduce direct and indirect transmission of CWD.