USGS Grapples with Chronic Wasting Disease

By Gail Moede and Dennis Heisey

Map showing where chronic wasting disease has been detected in North America. States that are shaded have detected CWD in captive herds. Pink (dark) shading indicates approximate areas where CWD has been found in wild populations.

Over the last year, chronic wasting disease (CWD) has been one of the most important wildlife management issues in the country. So far, the disease has been detected in wild deer and elk in eight States, three of those States within the last year. Virtually all State wildlife management agencies have actively inspected for CWD in their States. CWD affects elk, white-tailed deer, and mule deer but has not been documented in livestock or people. It is a disease of the nervous system, resulting in distinctive brain lesions, but its origins and route of transmission remain unknown. USGS scientists are collaborating with Federal, State, and Tribal partners to grapple with the challenges of this disease.

Image courtesy of Prionics AG, Schlieren, Switzerland.

Congress issued a directive in 2002 to create a National Plan for how Federal agencies will coordinate with others and assist in resolving the CWD problem. As the research bureau of the DOI, USGS was a major participant in creating the plan. The USGS sponsored a workshop to develop strategies for detecting and monitoring CWD in wild deer and elk. The multi-disciplinary group developed a comprehensive plan that included three primary objectives for a surveillance program: detection, assessment, and monitoring. Besides collaborating with the States of Wisconsin and Colorado and the U.S. Department of Agriculture, USGS continues to work on CWD with Tribal governments, the U.S. Fish and Wildlife Service, and the National Park Service.

The National Plan outlines six themes for action: Communication, Information dissemination, Diagnostics, Disease management, Surveillance, and Research (research is also a component of the previous three themes). The primary Federal role is to help coordinate and assist States, Tribes, other agencies with these action items. An Implementation Plan outlines and describes who is responsible for individual projects, what the projects will accomplish, the cost, and project time frames.

Elk and other members of the deer family may appear robust and healthy for several years after being infected with CWD.

The USGS is conducting scientific research needed for the effective management and control of CWD in free-ranging deer and elk. To manage the disease, we must know how the disease is transmitted from animal to animal and whether there are factors that make some animals more susceptible than others. The USGS is investigating potential disease transmission pathways by using genetic markers to establish kinship relationships, which will then be analyzed to determine potential disease transmission pathways. Of particular interest is whether social interactions between related does are important in disease transmission, as well as breeding activities that might transmit disease between does and bucks. This study is a natural companion to a USGS study that is examining whether genes can be identified that make animals more or less susceptible to disease. Knowing how the disease is transmitted from animal to animal, and whether some animals are innately more resistant than others, could have major implications for managing this disease in the field.

Another important question is whether CWD poses any risk to other native wildlife species, especially species that may be scavenging on the carcasses of CWD-infected deer, and how these species may serve to disperse the infectious agent across the landscape. USGS has several studies underway to examine these issues. Motion-sensing cameras will be used to conduct a study quantifying what species visit deer carcasses and how frequently for each species. They are also collecting small mammals from the CWD area of Wisconsin and performing tests to diagnose whether any of them have acquired CWD. In conjunction with this, laboratory studies are examining whether small mammals, such as mice and voles, can be infected with the disease and potentially serve as "bridge species" to allow the disease to be adapted and transmitted to other species.

Effective disease management requires reducing the risk factors that promote disease and disease spread. Identifying these risk factors is a first step. USGS is working with State agencies, National Park Service, and USDA to develop risk analysis tools. Understanding the risk for CWD transmission through feeding and baiting of deer is another disease management issue.

CWD was first observed in captive mule deer in Colorado in the late 1960's. In 1978, it was discovered in free-ranging wildlife and was found in southeast Wyoming. By the late 1990's, the disease was found in other States and Canada. For decades, CWD was considered a western concern, because it had been found in captive or free-ranging cervids (members of the deer family) only in a few States west of the Mississippi River. However, during 2002 CWD was discovered in free-ranging deer east of the Mississippi (Wisconsin and Illinois), as well as in New Mexico. With the discovery of CWD in 11 States and the potential widespread movement of affected species through alternative agriculture, CWD has become a truly national concern. USGS will continue working with our Federal, State, Tribal, and local partners to provide the science needed to combat this disease.