Chronic Wasting Disease (CWD) of Deer and Elk


Key Points

1. At this point there is no known cases of CWD in wild deer and elk in Oklahoma.

2. There has been no known transmission of CWD from deer or elk to any other animals or people even in states where CWD is found.

3. It is always wise to use common sense when handling any meat or when dealing with sick or injured animals.

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"In 2006 more than 1,626 hunter harvested deer and elk were sampled in Oklahoma and all tested negative for chronic wasting disease. To date, some 7,088 animals have been tested statewide as part of The Wildlife Department's monitoring program and all have tested negative for CWD. The Department will continue to monitor the state's deer and elk herds through additional testing."

What is Chronic Wasting Disease (CWD)?

It was 35 years ago and the biologists were baffled. Blood work showed nothing unusual, liver and kidney tests turned up negative for all known diseases, but the mule deer were still wasting away to skin and bones. It could have been straight out of an episode of “The X Files.”

A few of the captive deer at the Colorado Division of Wildlife’s research facilities in Fort Collins had begun to lose weight on a diet that sustained other deer. They drank incessantly and spent much of their time standing listlessly in their corrals. The biologists knew they had a unique syndrome on their hands, but it was like nothing they had ever seen before.

Captive deer at Wyoming Game and Fish Department's Sybille Research Unit were soon showing signs of the mystery disease. Because the Colorado and Wyoming facilities regularly traded deer and elk, the appearance of the disease in Wyoming came as no great surprise.

Over the next 10 years, researchers worked to understand the origin and causes of the affliction, but their studies led to more questions than answers.

One thing was certain, the disease was deadly. Between 1974 and 1979, 66 mule deer and one black-tailed deer were held captive in Colorado and Wyoming research corrals. Of those, 57 contracted the strange disease and not one survived.

The search went on for the cause of the disease. Viruses, bacteria and nutritional deficiencies were all ruled out. Biologists named it "chronic wasting disease” (CWD), identifying the disease’s most devastating outward symptom, irreversible weight loss.

The first break in the case came in 1978, when wildlife veterinarian Beth Williams began analyzing tissues of affected animals. She found microscopic holes in brain and nerve tissues of the deer. The disease was turning the brains of these deer into Swiss cheese.

This finding put Chronic Wasting Disease into a small category of diseases labeled transmissible spongiform encephalopathies (TSE). As pathologists looked into CWD further, they began to see similarities between it and scrapie, a TSE that affects sheep.

Sheep and goats have been affected by scrapie in Europe for centuries. In all those years, no other type of animal has ever come down with the disease, including generations of shepherds who work with their flocks daily and consumers who eat their meat and drink their milk.

Although they now knew CWD was related to scrapie and other TSEs, this helped little because at the time pathologists knew little about the cause of this disease either. The scientific camps began to stake their claim on the origins of these enigma diseases. Some thought it was a genetic illness, others assumed it was a virus too small to be detected by existing techniques. Several different scientists were pursuing proof of their favorite theories.

In the meantime, unsettling news was reported from the field. In March 1981, biologists in north Colorado brought in a sick elk that turned out to be suffering from chronic wasting disease. The disease had somehow spread from captive animals into free-ranging herds.

Cervids (animals such as white-tailed deer and elk ) seemed to be the target of CWD, no other animals including cattle, horses or humans have been affected by CWD. The disease spread incrementally through northcentral Colorado affecting mule deer, white-tailed deer and elk. In 1986, CWD claimed an elk in southeastern Wyoming, the first confirmed case of the disease in a wild animal outside of Colorado.

Although this was not exactly a raging disease outbreak, the spread of the disease had started and wildlife vets and biologists were concerned. They knew little about it, and knew nothing about how to stop it.

Today, 34 years since the disease was discovered, pathologists have learned more about the disease, but still have much to learn before they fully understand it. However slowly, CWD has continued to creep across the United States and Canada, currently impacting either captive or free-ranging deer in nine states and a pair of Canadian provinces. This includes a closely monitored captive elk herd in central Oklahoma.

It is now generally accepted that prions, naked proteins with the ability to duplicate and multiply, are the culprits to blame for CWD and other TSE’s. There remains no known cure or even a reliable method of disinfecting contaminated areas. Biologists in Fort Collins, Colorado, where the disease was first discovered, found out how resilient these prions can be. They set out in an intensive effort to rid the research facilities of CWD. All captive deer and elk were killed and buried. Personnel then plowed up the soil in the pens in an effort to bury possible disease organisms and structures and pastures were repeatedly treated with a powerful disinfectant. A year later, 12 elk calves from the wild were released in the sanitized holding areas. In the next five years, two of these elk died from chronic wasting disease.

Fortunately, Oklahoma’s free-ranging deer herd is not known to carry the disease. Over the past three years biologists and veterinarians have examined almost 400 deer and elk taken during Oklahoma's hunting seasons as part of the Department’s CWD monitoring program. All samples obtained from animals taken from the wild have tested negative and biologists will continue to closely monitor the deer and elk herd for signs of the disease.

Currently, detecting the disease is far from simple. The only acceptable test is a microscopic examination of an animal’s brain stem. There are no live animal tests and only a handful of laboratories and pathologists are qualified to administer the brain test.

If there is a bright side to chronic wasting disease it is that it reminds how valuable our deer are. It wasn’t that long ago that deer seemed headed down the same path as the buffalo and the passenger pigeon, over-exploited and pushed out by land-hungry settlers. Through the tireless work of biologists and sportsmen, deer have been restored to once unthinkable numbers in Oklahoma and across their native range.

A deer is a symbol of grace and it provides a succulent, nutritious meal. It is that and more, it is a wild animal that makes the woods a better place just for being there. It is as American as they come, inhabiting just about every ecotone on this continent.

To know that a disease as serious as CWD is spreading should pain everyone who has ever marveled at a deer slinking over a barbed wire fence. But it is no surprise that it was hunters who were the first to step up to the plate for the animals. In Oklahoma, a CWD monitoring program is in place thanks to funds provided through hunter’s licenses. In Wisconsin, it is hunters who have taken on the grim task of thinning out the deer herd to prevent the spread of CWD, and across the United States it is sportsmen who are carrying much of the financial burden to pay for biologists, veterinarians and pathologists to study the disease.

Is Venison Safe to Eat?

According to current research, there is no scientific evidence linking CWD to human diseases. It is recommended that hunters practice standard safety practices when handling any wild game, or any meat for that matter, as general precautionary measures.

These practices include washing your hands after handling raw meat and cooking the meat at an appropriate temperature.

"In my opinion, venison is just as safe as any other game meat," said Mike Shaw, head deer biologist for the Oklahoma Department of Wildlife Conservation.

Even in the parts of Wyoming and Colorado where chronic wasting disease is found, less than six percent of deer are infected.

A few precautions are recommended:

1) Don't shoot an animal that is acting abnormally or looks sick.
2) Wear rubber or latex gloves when you field-dress your animal.
3) Don't eat deer brains or spinal cord.
4) Bone out your deer meat and discard the brain, spinal cord, eyes, spleen, and lymph nodes.

Prions: New germs

In 1972 neurologist Stanley Prusiner lost a patient to Creutzfeldt-Jakob disease, a TSE that affect humans. Prusiner was serving his residency at the University of California’s School of Medicine and was astounded by the lack of information about the rare disease.

Two years later he set up his own laboratory at the University of California-San Francisco and set out to get to the root cause of scrapie, Creutzfeldt-Jakob and other TSE’s.

He took two known facts about the disease and came up with an astounding conclusion. He knew that scrapie infected tissue showed no signs of foreign DNA. He also knew that the only disinfectant techniques that affected the scrapie "germ" were those techniques that broke down not only DNA, but also proteins. From these two facts he assumed that the scrapie "germ" was a simple protein without DNA.

The notion seemed impossible in scientific circles. Since the 1950’s scientists had been working on the basis that proteins were duplicated using a blueprint provided by DNA. Prusiner was saying that these proteinaceous infectious particles, or prions for short, could recreate themselves without ever using DNA. His theory was accepted with just about the same enthusiasm that early mapmakers shared with Columbus when he told them the earth was round.

Prusiner spent the next two decades proving his theory and his efforts were rewarded in 1997 when he won the Nobel Prize for medicine. Although a few skeptics still remain, it is now generally accepted that prions play a causative role in CWD and other TSE’s.

The Worth of a Healthy Deer Herd

Wildlife agencies across the United States are scrambling to protect deer herds in their areas from the ravaging effects of CWD.

It is no wonder why. Not only are deer a beautiful natural resource and part of a rich hunting heritage, they also provide a significant economic impact. The annual pilgrimage of hunters into the woods each fall means big bucks, in more ways than one. In Oklahoma alone, 261,000 hunters, most of which are deer hunters, spent over $2.6 million on hunting expenditures according to a recent survey. While hunters are after deer, they spend money to gas their vehicles, eat meals and purchase equipment. These dollars go back into Oklahoma communities, particularly those in rural areas.

In an effort to keep Oklahoma’s deer safe from CWD, the Wildlife Conservation Commission has suspended the import of live deer and elk into the state from states that have CWD in their free-ranging deer herds. By suspending import of potentially infected animals, the Department hopes to avoid the consequences of the disease and the potential costs of controlling CWD. The detection of the disease has had immense economic impact on states such as Wisconsin where the disease was discovered last year. Within the first month after detection, the Wisconsin wildlife management agency spent approximately $250,000 in control and public information efforts and will spend upwards of $2.5 million this year as a result of CWD control efforts. The agency continues to try to control the spread of the disease and has publicly outlined plans to kill all 30,000 estimated animals in the focal area where infected animals have been found.

Wisconsin is not the only state fighting CWD. As an example, a supplemental appropriation of $300,143 has been made in Colorado to help combat the disease and more appropriations are being considered. Saskatchewan has spent approximately $30 million in attempts at eradicating the disease in infected commercially operated game farms.