Chronic Wasting Disease in Cervids in North America

Abstract

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy of free-ranging and farmed cervids in North America that is distinct from scrapie of domestic sheep, bovine spongiform encephalopathy, and Creutzfeldt-Jacob disease of humans. The purpose of this paper is to review the current status of CWD in North America. The natural host range of CWD includes mule deer (Odocoileus hemionus), white-tailed deer (Odocoileus virginianus), and Rocky Mountain elk (Cervus elaphus nelsoni). Experimentally, by intracerebral or oral exposure, the host range is wider, but there appears to be a significant barrier to infection of cattle and humans. The exact mechanism of CWD transmission is not known but recent studies indicate that direct transmission, indirect transmission via environmental contamination, and transmission associated with carcasses are possible. Maternal transmission does not appear to play a significant role in CWD. Although still under investigation, polymorphisms in the prion protein influence CWD pathogenesis in mule deer and elk. Studies of CWD pathogenesis following oral exposure demonstrate early widespread distribution of abnormal prion protein in the lymphoid tissue prior to invasion of the central nervous system. These data have lead to techniques for CWD surveillance in deer based on testing retropharyngeal lymph node. However, both brain and lymph node must be tested in elk for highest sensitivity due to differences in pathogenesis in this species compared to deer. The unique nature of a transmissible spongiform encephalopathy occurring in free-ranging cervids is a serious challenge to wildlife managers and animal health agencies in North America.