What is chronic wasting disease?
Chronic wasting disease (CWD) is a fatal neurological (brain and nervous system) disease that affects deer, elk, caribou, moose, and other members of the deer family (cervids). CWD is caused by a mutant protein, called a prion (pronounced pre-on). The disease is part of the group of diseases known as Transmissible Spongiform Encephalopathies (TSE) that includes scrapie in sheep and goats and bovine spongiform encephalopathy (i.e., mad cow disease) in cattle.
The disease is spread through direct contact with infected animals or through bodily fluids such as feces, saliva, or urine. Prions can remain active in the environment, binding to the soil and being taken up by plants, for at least 16 years and likely longer.
CWD is most commonly found in adult deer. The most obvious symptoms of the disease are weight loss, listlessness, excessive salivation, lowering of the head, and loss of coordination. There is no cure, no vaccine, no immunity, and currently no way to test for CWD in live animals. The disease is always fatal.
Where is CWD found in North America?
CWD was first identified in captive mule deer in a Colorado research facility in the 1960s. In 1981 the disease was identified in a wild elk in Colorado. In 1996, the disease was found in a captive elk farm in Saskatchewan, marking the first discovery outside of the Colorado/Wyoming “endemic zone.”
Since that time, CWD has been spread to additional states and provinces, primarily through the movement of captive deer and elk. The disease was discovered in Oneida County, New York, in 2005 in a captive deer herd and two free-ranging deer nearby. Intensive lethal sampling of free-ranging deer in the area since that time has discovered no more infected deer. More recently, CWD has moved into Pennsylvania, West Virginia, and Virginia and in 2018 CWD was found in Quebec.
For a listing of where CWD has been detected click here.
How common is CWD where it is found?
The occurrences of deer herds experiencing CWD are relatively limited in geographic distribution throughout North America. In some instances, the disease has only been discovered in captive farmed deer. There, where animals are fenced inside an area and tend to be in close physical contact, the captive deer have an infection rate as high as 80 percent or more. The greatest concerns occur where the disease has spread into the wild deer population. In Wisconsin’s core CWD area, more than 30% of adult bucks are infected with the disease.
Has CWD been found in Vermont?
CWD has not been found in Vermont, but in 2018 the disease was found in a captive red deer in Quebec Province, less than 100 miles from the Vermont border. The proximity of the disease is a wake-up call for Vermonters that every precaution must be taken to prevent the disease from entering the state.
During the period 2002 to 2009, the Vermont Fish & Wildlife Department sampled 400 hunter-harvested deer each year as part of its surveillance program for the disease. This level of sampling would detect CWD at a prevalence rate of 1 percent. Since that time, all wild ungulates exhibiting symptoms similar to CWD have been euthanized and tested and no infected deer have been found.
The department also asks Vermonters keep a watchful eye for signs of this illness in free-ranging deer and moose. Biologists and wardens respond to numerous calls about sick deer every year, and these calls make an important contribution to disease monitoring efforts.
What is the Vermont Fish & Wildlife Department doing to protect the deer herd from CWD?
The Vermont Fish & Wildlife Department and its regulatory arm, the Fish and Wildlife Board, have adopted several regulations that collectively reduce the chances of CWD entering Vermont. First, the Fish and Wildlife Board adopted a carcass importation rule for hunter-harvested cervids taken outside Vermont's borders. Only certain parts of the animal (such as the meat, antlers, and clean hide) may be brought into Vermont if the cervid was taken in a state or province that has had CWD or in any captive cervid facility.
The department maintains a list of previously infected states and provinces on the website and in the annual law digest. To legally import harvested deer, moose, or elk into Vermont, it is important to know what states and provinces have had infected animals.
Second, in 2015, the Board adopted a regulation prohibiting the use of cervid urine, blood, glands, gland oil, feces, or other bodily fluids for the purpose of taking or attempting to take deer. Captive white-tailed deer are the primary source of commercial urine-based lures and the prevalence of CWD in captive herds warrants Vermont’s actions. It is notable that since Vermont took this action, several other states have taken the same measure.
Third, the Board adopted a rule that bans baiting and feeding of deer - practices that could expose more deer to the disease should it occur in Vermont.
Lastly, the department has worked closely with the Vermont Agency of Agriculture Food & Markets to regulate captive cervid herds throughout the state. The department has effectively phased out captive deer and elk hunting facilities in Vermont. Also, the two state agencies have established regulations to reduce the risks posed by captive cervid facilities, although the risk of these facilities hosting or transmitting the disease to our wild deer populations remains.
Can you test for CWD?
Yes, but only in dead animals. There are no tests to detect CWD in a live animal. This is a major challenge for stopping this disease. An animal can be infected and spreading CWD for two years before it shows any symptoms. For this reason, even CWD-free certified captive cervid facilities that have yet to detect CWD in any of their animals cannot guarantee that the disease is not already within their herd.
Is venison safe to eat if the deer had CWD?
The Centers for Disease Control state that to date, there have been no reported cases of CWD infection in people. However, animal studies suggest CWD poses a risk to some types of non-human primates, like monkeys, that eat meat from CWD-infected animals or come in contact with brain or body fluids from infected deer or elk. These studies raise concerns that there may also be a risk to people. Since 1997, the World Health Organization has recommended that it is important to keep the agents of all known prion diseases from entering the human food chain.
The World Health Organization (WHO) says there is no scientific evidence CWD can infect humans. However, WHO also suggests no part of a deer or elk with evidence of CWD should be eaten by people or other animals. In states where CWD is found, hunters are asked to dress the carcass without cutting the spinal cord, brain, eyes, lymph nodes, and tonsils.
Until a reliable conclusion can be drawn, the safest approach would be to not eat meat from animals appearing sick and from regions of the country where CWD is known to occur. That is another reason why it is so important to prevent CWD from entering Vermont.
Can people get CWD?
According to public health (Centers for Disease Control, World Health Organization) and animal health officials, data available to date indicate that chronic wasting disease is not currently known to be naturally transmitted to humans, or to animals other than the deer family. Data from recent molecular studies provide quantitative evidence of the apparent difficulty of cross-species transmission.
CWD is still not known to have infected any humans, but the mutant protein has been shown to have adaptive potential, so caution is still appropriate. As a general precaution, public health officials recommend that people avoid contact with deer, elk, or any other wild animal that appears sick.
Although there's no evidence that CWD can be naturally transmitted to domestic livestock, CWD is similar in some respects to two livestock diseases:
- Scrapie, which affects domestic sheep and goats worldwide and has been recognized for over 200 years.
- Bovine spongiform encephalopathy (BSE), which is a more recent disease of cattle in the United Kingdom and Europe.
Despite some similarities, there is no evidence suggesting either scrapie or BSE are caused by contact with wild deer or elk, or that wild deer or elk can contract either scrapie or BSE in countries where these diseases occur.
How can CWD be prevented?
There are measures people can take to help minimize the chances of CWD entering Vermont. These include:
- Follow state regulations prohibiting the use of urine-based deer lures. Use synthetic lues instead.
- Follow state regulations prohibiting the importation of deer, moose, or elk carcasses into Vermont from any of the CWD states or provinces listed on the department website.
- Report any sick-acting deer or moose to the department, primarily to your local game warden.
- Report any escaped non-native deer or elk to the department immediately.
- Do not feed white-tailed deer at any time of year to prevent the spread of diseases among concentrations of animals.
Can CWD be eradicated after it’s introduced into a new area?
There is some hope because New York may have managed to do just that. Many states have tried and failed to eradicate CWD when it was found.
Many southern and mid-western states have deer densities ranging from 50 to 100 deer per square-mile. In such situations, the disease can be expected to spread more rapidly, making it difficult to contain or eradicate CWD before it becomes established in the population.
Wisconsin spent more than 30 million dollars trying to eradicate the disease by depopulating free-ranging deer but failed. Scientific research later indicated that CWD was present in Wisconsin over a decade before it was discovered, so disease eradication efforts there were just too late.
Other states have not attempted to eradicate CWD when it was first recognized. These states have deer densities of over 50 deer per square-mile, making disease eradication unlikely. Management decisions to depopulate free-ranging deer are also politically unpopular.
The department has a CWD Strategic Management and Response Plan. The scientific consensus is that when CWD is first detected in a new area, disease eradication should be attempted if it is deemed possible.
Eradication of CWD may be achieved if free-ranging deer can be depopulated to 0 to 5 deer per square-mile for a period of at least 5 years in an area within about 10 miles of the location where the initial infected animal was found. That is an area of about 300 square miles. With few or no deer to spread the disease, the infectious prions that cause CWD diminish over time.
Disease eradication is possible in Vermont because:
- Local deer densities in Vermont are relatively low and range from 5 to 30 deer per square mile.
- Depopulating winter concentrations of deer would be relatively easy to do and would effectively cover larger areas.
- CWD should be less than 1 percent prevalent in the population when it is first detected because a sick deer would be relatively visible in Vermont. This is why it’s important for Vermonters to report seeing sick deer.
There is just one chance to eradicate CWD when it is first discovered, and it’s the department's legal duty to see that the health of Vermont's deer herd is protected. It may not be a popular action to take, but it will be necessary to try to eradicate the disease for the sake of the deer and deer hunting tradition.
Where can I learn more about chronic wasting disease?