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Chronic Wasting Disease


Fri, Nov 1st, 2002
Posted in Features

CWD, or Chronic Wasting Disease has received a lot of press recently as deer hunters prepare for the season. This disease occurs naturally in North American deer and Rocky Mountain Elk. It belongs to a family of diseases known as transmissible spongiform encephalopathies, (TSE). Similar diseases include scrapie of sheep and bovine spongiform encephalopathy (BSE) or ‘Mad Cow Disease.’

CWD has been around awhile, first discovered in 1967 in northern Colorado. Captive deer at a wildlife research station showed signs of ‘wasting away.’ Chronic weight loss is the first sign of the disease, followed by disorientation, drooping head or ears, poor body condition, tremors, stumbling, increased salivation, difficulty swallowing, or excessive thirst or urination. The disease is progressive and always fatal. In captive animals it has been noted that diseased animals continue to eat grain but may show decreased interest in hay.

It was 1978 when researchers classified the disease, spongiform, because of the sponge-like holes in brain tissue found in diseased animals. A few years later, in 1982, researcher Stanley Pruisner, named the unusual proteins found in spongiform encephalopathies, prion proteins. These prion proteins are usually harmless and necessary for brain cells. Somehow, and researchers are still unsure of how, these prion proteins fold into abnormal shapes eventually causing sponge-like holes to form in the brain tissue.

What triggers the prion proteins to fold abnormally in the brains of a diseased deer or elk is currently under a lot of speculation. It appears to take from months to years from the time an animal is infected to when it shows signs of the disease.

One current working theory, as to how CWD is contracted, is by ultra-small viruses called virinos that cause the normal prion proteins to fold into the diseased prion form. How these virinos might pass from one animal to another is unknown. The virino theory is yet to be proven.

By the mid 1980’s CWD was detected in free ranging deer and elk in northern Colorado and SE Wyoming and has since been detected in wild or captive animals in South Dakota, Nebraska, Kansas, Oklahoma, New Mexico, Montana, Wisconsin, Saskatchewan and Alberta. The disease has yet to be detected in Minnesota’s wild deer population, however, CWD was recently discovered in a single captive elk in Aitkin County, Minnesota.

The Aitken County elk herd containing CWD was quarantined this past August. The entire herd was destroyed by State Board of Animal Health. Last week they announced that all 48 elk tested negative for CWD. Minnesota Board of Animal Health Executive Director, Bill Hartmann, said these results are encouraging.

"To date all testing in farmed and free-ranging deer in Aitkin County has been negative," Hartmann said. "We are encouraged that preliminary results indicate that CWD has not spread from the single infected animal."

Because the mode of transmission is still unknown, MN DNR has initiated a plan to cull and test free ranging deer from Aitken County area. For more than a year, the DNR has been testing "suspect" deer that are found sick or displaying symptoms consistent with CWD. None have been found positive. The DNR plans to test 5,000 hunter-harvested deer this fall. Wildlife officials will collect samples from 1-year-old or older deer at 15 of 130 hunting permit areas across the state. Only deer from specific, targeted areas will be sampled.

This fall's testing will provide DNR biologists with a basis for early detection of the disease in Minnesota. The DNR reports that continued testing will be necessary to detect the disease at its early stages and possibly eradicate it.

Wisconsin DNR began testing wild deer for CWD in 1999. Their first confirmed case was in February of 2002. Wisconsin has initiated a mass culling, or ‘depopulation’ program after testing over 500 deer from a 450-mile surveillance zone and finding a total of eighteen deer positive for CWD. Wisconsin DNR plans to continue collecting samples throughout their disease eradication process. Wisconsin, along with 22 other states, has banned the import of any deer, elk or mule deer.

Last year the National Veterinary Services Lab in Ames, Iowa found three deer testing positive for CWD in unit 70A, or eastern Iowa and western Dane County.

Are You At Risk?

The biggest question facing deer hunters today is to whether or not humans are at risk of contracting the disease or becoming sick from eating venison. According to WHO, the World Health Organization, there is no risk of humans contracting CWD.

There is currently no scientific evidence that CWD has or can be spread to humans, either through contact with infected animals or by eating the meat of infected animals. The Center for Disease Control has conducted an exhaustive study of CWD and human risk and has stated: "The risk of infection with the CWD agent among hunters is extremely small, if it exists at all."

However, as we are still learning about this disease, it is recommended that hunters take precautions to limit risks. First and foremost, do not harvest any animal that appears sick or is acting strange. Note the animal’s location and contact your local conservation officer, area wildlife manager or the DNR.

Is it safe to eat venison

this year?

Meat from deer or elk should be safe to eat, according to officials at the Minnesota Department of Health, provided that hunters take the following precautions:

• Don't eat meat from animals that look sick or ill.

• Don't eat the brain, spinal cord, eyes, spleen, tonsils and lymph nodes.

• Dress the animal properly -- minimize handling of brain and spinal tissues, wear rubber gloves when field dressing carcasses and wash hands and instruments thoroughly after field dressing is complete.

• The DNR also urges hunters to avoid bringing back whole carcasses from animals harvested in other states. The safest way to transport carcasses is to bring back only cut and wrapped meat, boneless meat, hides, and antlers or cleaned skull plates.

Testing Issues

There is currently a shortage of USDA-certified testing laboratories. In Minnesota, the DNR will not be testing deer for hunters outside of the target areas. There are several veterinary clinics providing testing in and around Fillmore County, (see sidebar).

Currently any testing must be done on brain or lymph tissues taken only from a deceased deer. Research is underway to develop a method for testing live animals.

Local Processors

You can expect your local meat locker will require that any venison brought in for processing must be completely removed from bone. Litscher Locker of Rushford reported that they do not believe the venison to be dangerous, but they are taking precautions because their other (beef and pork) customers do not want any risk of exposure. Until more is known about CWD, even though it has been declared safe, precautions are being taken.

The Minnesota Department of Natural Resources is asking firearms deer hunters who harvest an adult deer in one of the permit areas selected for Chronic Wasting Disease testing to register it as soon as possible so that good samples could be obtained for testing.The DNR plans to test between 5,000 and 6,000 hunter-harvested deer during the 2002 firearms deer season, which begins November 9. Selected registration stations will be staffed for CWD sampling starting at noon on Saturday, November 9. As needed, stations will be staffed again on Sunday, November 10, starting at 9:00 a.m. Stations in southeast Minnesota will be staffed again starting noon on November 23 for the start of Zone 3B season. Submission for sampling is voluntary. Hunters who register their deer at a registration station where samples are being collected may be asked several questions about where the deer was harvested. Taking a sample requires removing the head from the carcass. Hunters who want to submit a head but retain the antlers may saw off the skull plate before surrendering the head.Permit areas selected for hunter-harvested testing were chosen based on their geographic location and other factors.Hunters who are not asked to submit their deer to the DNR for testing and who are interested in getting it tested may have their deer tested for a fee at the University of Minnesota. Selected veterinarians across the state have agreed to extract samples and send them for testing.Local Area CWD Sampling Stations•Good Sport, St. Charles;•Larry’s Mobile, Rushford;•Tri-State Bait, La Crescent;•Food Mart, Houston.

Fillmore County Area Veterinary Clinics for CWD testing•Spring Valley-LeRoy Clinic (507) 346-2734;•Chosen Valley Vet Clinic (507) 867-3610;•Caledonia Vet Service (507) 725-3380;•Eyota Vet Clinic (507) 545-2828. Source: Minnesota DNR

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