Chronic wasting disease

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Impact on deer population remains largely unknown

A new case of chronic wasting disease (CWD) was discovered recently in a Park County white-tail deer in deer Hunt Area 112, southwest of Cody.

The disease has been spreading slowly across the state. How it will impact the deer population in the future remains unknown.

Chronic wasting disease is a fatal neurological disease affecting elk, deer and moose.

Chronic wasting disease attacks the nervous system and results in distinctive brain lesions in species such as deer, elk and moose.

Wyoming is the North American hotbed for the disease, a typically fatal illness for which no treatment is currently known, according to the U.S. Geological Survey’s National Wildlife Health Center.

It remains unknown exactly how the disease is transmitted, but there is speculation that transmission could be lateral (from mule deer to elk) or maternal (from mother to newborn). 

Symptoms include gradual weight loss, excessive drinking and urination. The brain lesions lead to behavioral changes in most cases, including decreased interactions with other animals, listlessness, lowering of the head, blank facial expression and repetitive walking in set patterns, according to the Chronic Wasting Disease Alliance.

For elk, behavior changes can include hyper-excitability, nervousness, excessive salivation, drooling and teeth-grinding.

Deer seem to be most susceptible and moose least susceptible, according to the Wyoming Game and Fish Department.

The first cases of the disease were reported in the 1970s in the Fort Collins, Colorado area, said Tim Woolley, Game and Fish Cody wildlife management coordinator.

Chronic wasting disease areas for deer span most of the state, including much of Park County, according to a Game and Fish map. Portions of southwest Wyoming appear free of the disease at this time, with the exception of deer Hunt Area 132 around Mountain View.

Last year's analysis

A total of 1,632 deer, elk, and moose samples were analyzed in 2014, according to Game and Fish. Of those sampled, 110 tested positive for chronic wasting disease. That breaks down into:

• 83 mule deer,

• 12 white-tailed deer, and

• 15 elk.

The 2014 surveillance efforts identified seven new deer hunt areas — 36 near Shoshoni, 84 and 98 east of Rawlins, 97 near Muddy Gap, 116 by Meeteetse, 123 in the Lovell area and 160 near Lander. Hunt Area 108 was the lone elk area identified.

Of the 1,632 total samples received, 86 percent were from hunter-killed animals, 8 percent from targeted animals and 6 percent from road-killed deer, elk and moose.

The proportion of positive samples in each of the categories was 5.6 percent (79 of 1,403) for hunter-killed animals, 23 percent (30 of 129) for targeted animals and 1 percent (1 of 100) in road-killed animals. Areas where the disease affects deer appears to be slowly but steadily increasing.

Hank Edwards, Wyoming Game and Fish Department disease specialist in Laramie, said he believes chronic wasting disease will continue to progress, but he has no idea how far it will expand. He said he knows it will impact the population. “We just don’t know what kind of effect it will have.”

Chronic wasting disease in elk

It seems like elk always have a lower prevalence rate for CWD, Woolley said.

The disease is found in elk predominately in southwest Wyoming.

Biologists are not sure why they see fewer cases of CWD-positive elk. One theory is that elk could have a higher resistance to the disease, Edwards said. “There is so much we don’t know about the disease.”

Since 2005, moose have been included in the CWD surveillance program, according to the Game and Fish. As of last year, 750 moose have been sampled.

“We’ve only had one positive moose in the state,” and that was in 2008, Edwards said.  However, Colorado has CWD-positive moose.

Don't eat meat from CWD-positive animals

Research on non-human surrogates — primates and mice — has indicated that humans are not likely to contract CWD from contacting or eating an infected animal. However, CWD is one of a group of diseases termed transmissible spongiform encephalopathies, or TSEs. Bovine spongiform encephalopahty (aka mad cow disease) is a TSE that has been implicated in causing human deaths. Thus, human health agencies caution that animals known to be infected by chronic wasting disease should not be consumed by humans, according to information from the Game and Fish Department.

Chronic wasting disease is not known to be a disease of humans. However, some people in Europe contracted variant Creutzfeldt-Jakob disease, presumably after eating beef contaminated with mad cow disease prion proteins. Consequently, some fear that humans also could develop a transmissible spongiform encephalopathy after eating CWD-infected venison. Thus far, there is no evidence that this is likely, according to the department.

Studies conducted by the Wyoming Game and Fish Department, the University of Wyoming and the Colorado Division of Wildlife concluded it is highly unlikely that domestic cattle can contract chronic wasting disease.

Vaccine

A vaccine developed against chronic wasting disease has not showed much promise, Edwards said.

The search for a vaccine still is underway, but that may be sometime in the future before one is developed. Once it is, the big question is how to administer the vaccine to thousands of deer. “I think this is going to be a tough bug to solve,” Edwards said.

Humans should take great care handling animals with chronic wasting disease (CWD), according to the Wyoming Game and Fish Department.

Handling precautions

State public health officials and Game and Fish recommend taking the following simple precautions when handling deer or elk carcasses where CWD occurs:

• Wear rubber or latex gloves as a routine precaution when field dressing.

• Meat should be boned out when butchering.

• Hunters should not harvest or eat wild animals that appear sick.

• For disinfecting utensils of the prion protein, use sodium hypochlorite (household bleach, greater than 2 percent free chlorine: One part bleach to 1.5 parts water at room temperature for one hour, or sodium hydroxide (caustic soda, soda lye, 38 grams in one liter of water at room temperature for one hour).

Contact the local game warden, biologist or regional Game and Fish office if a deer or elk looks sick.

Although natural occurrences have not been documented, recent research indicates intact carcasses from deer that died of CWD may spread the disease to healthy deer. To minimize this possibility, the department recommends that deer and elk hunters transport only the following items from areas where CWD is known to exist:

• Cut and wrapped meat.

• Boned meat.

• Animal quarters or other pieces with no portion of the spinal column or head attached.

• Hides without the heads.

• Cleaned (no meat or other tissue attached) skull plates with antlers attached.

• Antlers with no meat or other tissue attached.

Surveillance efforts

The Game and Fish will continue CWD surveys. Tissue samples will be collected from harvested deer and elk at selected check stations and meat processing facilities. Hunter participation is voluntary. Surveys help the department monitor CWD in Wyoming.

Risk

There is no evidence of CWD being transmitted to humans, according to the World Health Organization in 1999 and Dr. Ermias Belay of the Center for Disease Control in 2004.

Nonetheless, to avoid any risk, both organizations say parts or products from any animal that looks sick or tests positive for CWD or other TSEs should not be eaten, according to the Game and Fish.

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