Chronic wasting disease (CWD) is a progressive, fatal, degenerative neurological disease occurring in farmed and free-ranging deer, elk, reindeer (caribou), and moose. The disease was first recognized in 1967 as a clinical ‘wasting’ syndrome of unknown cause in captive mule deer in Colorado. CWD belongs to the family of diseases known as transmissible spongiform encephalopathies (TSEs). TSEs include a number of different diseases affecting animals and humans including bovine spongiform encephalopathy (commonly known as “Mad Cow Disease”) in cattle, scrapie in sheep and goats, and Creutzfeldt-Jacob disease in humans. Although CWD shares certain features with other TSEs, it is a distinct disease affecting only members of the cervid family. There is no known treatment or vaccine for CWD.
CWD is a slow and progressive disease. Because the disease has a long incubation period, deer, elk, reindeer, and moose infected with CWD may not present any visible signs of the disease for up to two years after they become infected. As the disease progresses, cervids with CWD show changes in behavior and appearance. These clinical signs may include progressive weight loss, stumbling, tremors, lack of coordination, blank facial expressions, excessive salivation and drooling, loss of appetite, excessive thirst and urination, listlessness, abnormal head posture, and drooping ears.
The agent that causes CWD and other TSEs has not been completely characterized. However, the theory supported by most scientists is that TSE diseases are caused by proteins called prions. The exact mechanism of transmission is unclear, although evidence suggests CWD is transmitted directly from one animal to another through bodily fluids and tissues or through contact with infectious agents present in the environment. CWD is of increasing concern for wildlife managers across North America.
The number one objective in the management of CWD is to prevent its spread into new areas. In an attempt to prevent or slow the spread of CWD to new areas, many states have passed regulations banning the transportation of live animals or carcasses originating in CWD-positive states, begun implementing regulations similar to or more stringent than the guidelines for the United States Department of Agriculture’s CWD Herd Certification Programs for farmed cervid facilities, and/or have banned deer baiting (which congregates animals and allows for possible transmission through direct contact or environmental contamination). Several states have also recently adopted regulations banning the use of urine-based attractants for white-tailed deer.
Points of Interest
- Although no cases of CWD have been found in humans yet, a recent study conducted in Canada indicated that the spread of CWD in humans might be possible. The study found that macaque monkeys contracted CWD from eating contaminated deer meat, though the results of this study have not yet been published in a peer-reviewed scientific journal.
- Alternatively, a study published in the Journal of Virology in 2018 detected no evidence that CWD had been transmitted to macaques, though the CDC notes that there is no known explanation for the differences in these results and suggests humans avoid exposure to CWD.
- CWD has currently been detected in 30 states: Alabama, Arkansas, Colorado, Idaho, Illinois, Iowa, Kansas, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Virginia, West Virginia, Wisconsin, and Wyoming.
- Only boned out meat, antlers, skull-plates cleaned of any soft tissue, hides, and ivories should be transported from CWD contaminated areas to prevent environmental contamination through movement of carcasses.
- A recently tested vaccine in Wyoming resulted in a potential negative effect associated with the vaccine, in that inoculated elk were found to be about seven times more likely to develop CWD than untreated animals.
- Research in 2015 indicated that grass plants can bind, uptake and transport infectious prions, complicating containment strategies in agricultural areas.
- Norway has now banned the import of hay and straw from U.S. states where CWD has been detected, and all imports must be accompanied by a certificate from a veterinarian certifying the product is from a CWD-free area.
- Currently, thirteen states (Alaska, Arkansas, Arizona, Connecticut, Idaho, New Jersey, New Mexico, Nevada, Oregon, Rhode Island, South Carolina, Vermont, and Virginia) now ban the use of deer urine or excretion collected from cervids as an attractant, while several others restrict its use in all or part of the states or require specific testing criteria to be met.
- In 2017, Montana enacted SB 173, calling for a ban on any urine that is not from confirmed CWD-free herds (Archery Trade Association approved). In 2018, Michigan also changed their rules to allow only those urine-products that are certified CWD-free through the Archery Trade Association program.
- Beginning in 2019 throughout South Carolina, “it is illegal to possess or use, for the purpose of hunting or scouting any wild animal in S.C., any substance or material that contains or purports to contain any excretion collected from a cervid (deer) including urine, feces, blood, gland oil, or other body fluid.”
- Many other state agencies strongly recommend that hunters do not use urine-based attractants out of fear of spreading CWD.
- Additional states are considering banning urine in the near future through the development of CWD-response plans.
- Additionally, in 2019, the Michigan Natural Resources Commission approved an immediate ban on baiting and feeding deer for the Core CWD Surveillance Areas in order to limit the spread of CWD.
- For a list of current state regulations concerning CWD and to review the status of CWD in your state, please visit the Chronic Wasting Disease Alliance at: http://cwd-info.org/map-chronic-wasting-disease-in-north-america/.
Responses to the potential spread of CWD vary by state depending on the perceived level of risk and the concerns of stakeholders. State legislators are encouraged to educate themselves on the status of CWD in their state and to work with their fish and wildlife agency to determine what protections are needed in their state to prevent the spread of CWD within their boundaries. Generally, increased attention to and funding for regular screening and testing of cervids within a state is necessary to ensure that a timely response to a CWD outbreak is possible.