Chronic Wasting Disease of Deer and Elk: A Review with Recommendations for Management

Abstract

Chronic wasting disease (CWD) has emerged as an important disease of wild and farmed cervids in North America. Of the transmissible spongiform encephalopathies (TSEs), or prion diseases, CWD is the only 1 found in free-ranging species. Because the TSEs include infamous diseases like bovine spongiform encephalopathy (BSE) of cattle and variant Creutzfeldt-Jakob disease of humans, CWD by association has become a disease of interest beyond the parochial concerns where it is found. Consequently, wildlife managers are faced with developing programs for addressing CWD. Mule deer (Odocoileus hemionus), white-tailed deer (O. virginianus), and Rocky Mountain elk (Cervus elaphus nelsoni) are the only species known to be naturally susceptible to CWD. Although implications of CWD are not entirely clear at this time, we know that CWD is a fatal, contagious disease of mature reproductive segments of deer and elk populations. It has been endemic in free-ranging cervids in a core area of contiguous portions of southeastern Wyoming and northeastern Colorado, USA, for a minimum of 20 years and probably longer. The known geographic distribution of endemic CWD is relatively limited at this time, although as results of intensified surveillance become available, this may change. Foci of CWD in free-ranging deer have been identified distant from the core endemic area as far east as Wisconsin. Distribution has greatly expanded in the last decade or more via commerce in infected farmed elk; as a result, CWD recently has been found in multiple jurisdictions of the plains, foothills, and Rocky Mountains of western North America, and in South Korea. Studies of the biology and natural history of CWD over the last few years have resulted in a better understanding of its pathogenesis and epidemiology. Chronic wasting disease is transmitted horizontally from infected to susceptible cervids. Early involvement of alimentary tract-associated lymphoid tissues during incubation suggests plausible routes for transmission via feces or saliva. Residual environmental contamination also appears to be important in sustaining epidemics. Studies of CWD epidemiology led to development of models to help explain the history of CWD as well as forecast its impacts on deer and elk populations. Improved tests allow CWD to be diagnosed early in incubation, long before clinical signs appear. Where CWD is not known to occur, managers should be, and in some cases are, developing surveillance programs and regulations that prevent or reduce the likelihood that CWD will be introduced into their jurisdictions. Where CWD is already endemic, responsible agencies are conducting surveillance to assess status and trends in prevalence and geographic distribution, managing deer and elk populations to limit spread, and developing and evaluating techniques for further controlling and perhaps eradicating CWD. Programs for addressing the challenges of CWD management will require interagency cooperation, commitment of funds and personnel, and applied research.