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Questions and Answers: Chronic Wasting Disease

1. What is Chronic Wasting Disease?

Chronic Wasting Disease (CWD) is a newly recognized disease threat to North American deer and elk populations. CWD is a brain disease similar to Bovine Spongiform Encephalopathy, also known as "Mad Cow Disease." CWD is known to affect elk, moose, mule deer, and white-tailed deer - members of the North American cervid family.

Ten years ago, it was diagnosed in free-ranging deer and elk primarily in northeastern Colorado and southeastern Wyoming and adjacent Nebraska, but also was found in captive elk in Colorado, Kansas, Montana, Nebraska, Oklahoma, Saskatchewan, and South Dakota. Since that time, CWD has been spread eastward across the Mississippi River by the captive deer trade. Michigan found its first case of CWD to be in a captive deer herd in 2008. The disease was discovered in Oneida County, New York, in 2005 in a captive deer herd and 2 free-ranging deer nearby. Intensive lethal sampling of free-ranging deer in the area has discovered no more infected deer as of 2009.
CWD is caused by a mutant protein, called a prion. CWD is spread by close contact between animals. Animals exposed to a CWD-contaminated environment also may become infected. Special laboratory techniques have been used to show that prions can be shed in saliva, blood, urine, feces, antler velvet, and body fat. Prions bind to soil where they can remain infectious for years.

Usually, months to years pass before an infected animal shows signs of the disease even when an infected deer or moose is contagious. Classic signs of CWD in animals aged18 months or older, include emaciation, drooping head and ears, listlessness, grinding of teeth, increased salivation, and excessive thirst and urination. CWD is always fatal to infected cervids.

There has been no way to test a live animal for CWD. Scientists must microscopically examine the brain from a recently dead animal to detect credible signs of the disease. Researchers have tried to develop a live-animal test using tonsil biopsies and rectal swabs, but live-tests remain unreliable.

2. How common is CWD?

It is thought to be relatively uncommon, but is likely more common where deer or elk densities are high. Examinations of wild deer and elk where CWD has been found indicate about 1% to 5% of the animals are infected. Under captive circumstances or in high-density free-ranging deer populations, where animals tend to be in physically closer living conditions, the infection rate is as high as 15%.

3. Has CWD been found in Vermont?

CWD has not been found in Vermont. The Vermont Fish and Wildlife Department has been sampling 400 hunter-harvested deer per year since 2002 and no infected deer have been found. The department also asks that Vermonters keep a watchful eye for signs of this illness in free-ranging deer and moose. Biologists and wardens respond to several calls about sick deer every year, and these calls make an important contribution to disease monitoring efforts. The department maintains a list of previously infected states and provinces on their 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.

4. What is the Vermont Fish and Wildlife Department doing to protect the deer herd from CWD?

The Fish and Wildlife Department, in cooperation with the state's Agency of Agriculture, issued a moratorium effective May 1, 2002 on the importation into Vermont of all cervids (deer and elk family) used for farming, exhibitions, and shooting purposes. The Agency of Agriculture maintains the moratorium for cervids of questionable origin. 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 and skinned hide) may be brought into Vermont if the cervid was taken in a state or province that has had CWD. The Board adopted a rule that bans baiting and feeding of deer - practices that could expose more deer to the disease. In 2009, there was a new rule that places captive deer hunting facilities under the jurisdiction of the Fish and Wildlife Department with greater enforcement capability to see that such facilities follow disease prevention and testing regulations. Also, the department tries to maintain free-ranging deer densities at less than 20 deer per square-mile by using hunters to harvest enough adult female deer annually. Having relatively low deer densities (compared to other southern and midwestern states) may prevent the disease from spreading rapidly if it gets here and may allow the department to eradicate the disease when it is initially found and before it becomes well established.

5. Is venison safe to eat?

The World Health Organization (WHO) has said there is no scientific evidence CWD can infect humans. However, WHO also says 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 deer meat from from animals appearing sick and from regions of the country where CWD is known to occur.

6. 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. As a general precaution, however, 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, and 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. 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.

7. How do you test for CWD?

To test for CWD a small piece of brain tissue is examined under a microscope for the presence of the causative prions. A list of Laboratories that can test for CWD may be found in the Library section of the Vermont Fish and Wildlife Webpage..

8. Will the Vermont Fish and Wildlife Department pay to test my deer?

No. You will have to cover that cost yourself. However, the department will be testing a predetermined number of hunter-killed deer to estimate the probability of CWD occurring in Vermont.

9. How can CWD be prevented?

There is no know vaccine nor is there a cure for infected animals. Researchers believe that CWD is transmitted by direct contact between animals. Preventing direct contact can be accomplished in several ways. Prevent live animals and whole carcasses of an unknown health background from entering the state. Eliminate artificial feeding sites and other circumstances that lead to high densities of deer (e.g. uncontrolled population growth). Monitor and enforce disease testing and prevention regulations for the captive deer industry. Investigate the risk of urine-based scent lures that are obtained from captive deer.

10. Can CWD be eradicated after it is introduced into a new area?

There is 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 midwestern states have deer densities ranging from 50 to 100 deer per square-mile. In such situations, the disease can be expected to spread rapidly, making it difficult to contain or eradicate CWD before it becomes established in more than 1% of the population. Wisconsin spent millions of 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 Vermont Fish and Wildlife Department will be updating and finalizing its CWD Strategic Management and Response Plan in 2010. Most North American state and provincial wildlife agencies have such plans. 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 can 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 a area within about 10 miles of the location where the initial infected deer or moose 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 die after a few years. Disease eradication is possible in Vermont because: 1) local deer densities in Vermont are relatively low and range from 5 to 25 deer per square mile; 2) depopulating winter concentrations of deer would be relatively easy to do and would effectively cover larger areas; and 3) CWD should be less than 1% prevalent in the population when it is first detected because a sick deer would be relatively visible in Vermont. The last point is why it is important that Vermonters report seeing sick deer with the symptoms described above.

There is just one chance to eradicate CWD when it is first discovered, and it is 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 themselves.

11. Where can I learn more about Chronic Wasting Disease?


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