Writer: D'Lyn Ford
LAS CRUCES - Chronic wasting disease has been identified in just one deer in New Mexico six months ago, but the fatal brain illness, related to "mad cow" disease, has hunters and wildlife experts concerned about eating venison as hunting season nears.
"First and foremost, do not shoot, handle or consume any animal that appears sick," said Jon Boren, a wildlife specialist with New Mexico State University's Cooperative Extension Service. "If you observe a sick animal, contact the New Mexico Department of Game and Fish. It just makes sense to take some precautions to minimize any potential for risk." Hunting season starts in September and continues for several months.
His recommendations include wearing rubber gloves when butchering and boning game meat, and minimizing contact with animal's brains, lymph nodes and spinal cords. Also, hunters should wash their hands and knives thoroughly after field dressing, and avoid consuming tissue other than the meat because prior research indicates that the malady doesn't accumulate in muscle tissues.
Chronic wasting disease is a type of transmissible spongiform encephalopathy, a group of diseases that also includes mad cow disease in cattle and scrapie disease in sheep. However, chronic wasting disease is significantly different from mad cow disease and scrapie. The disease attacks the central nervous systems of infected animals and is always fatal.
Boren said infected animals drink excessive amounts of water and lose control of their sense of balance and bodily functions. Affected brain tissue starts to take on a sponge-like appearance when viewed through a microscope. In later stages, animals show signs of progressive weight loss and eventually death.
There is no evidence chronic wasting disease can spread to humans.
"In all probability, transmission from one animal to another is through body fluids like feces, urine or saliva," Boren explained. "Animals that are crowded or confined also have a greater chance of encountering the body fluids of other animals, and therefore a higher likelihood of becoming infected."
The mysterious wildlife disease isn't new. First identified in 1967, it has been found in free-ranging deer and elk in Colorado, Wyoming, Nebraska, South Dakota, Wisconsin, New Mexico and the Canadian province of Saskatchewan, as well as at commercial deer and elk ranches in six states and two Canadian provinces.
"The first and only documented case of chronic wasting disease in New Mexico was from a wild mule deer collected on March 28 from the White Sands Missile Range," Boren said. It was a discovery that has perplexed experts, who were stunned to find the disease hundreds of miles from infected populations and about 100 miles from the nearest captive herd.
The brain-destroying illness is caused by an abnormal protein, called a prion, that causes other normal proteins to fold abnormally in the brain. Prions are incredibly tough, since they can withstand high temperatures and survive in soil for years.
Chronic wasting disease is thought to be harbored in brain and spinal tissue of infected animals, which is why it is difficult to test live animals for the disease. Testing requires the brain stem to be sent to a lab where tissues can undergo immunohisto chemistry to detect chronic wasting disease prions.
"Brain samples must be taken within 48 hours of the animal's death in order to be tested," Boren said.
One concern among experts is that animals can be infected with chronic wasting disease for months or years before outward signs of infection are evident. It's one reason New Mexico officials have already moved to adopt new rules restricting importation of deer and elk from states where the disease is known to exist.
State wildlife officials have also been testing the brain stems of deer and elk for several hunting seasons to determine any presence of the disease. That sampling effort is now being greatly expanded across the state. Hunters can get their animals tested through the New Mexico Department of Game and Fish.
In addition, new research efforts are underway. Lou Bender, a research biologist with NMSU's Cooperative Fish and Wildlife Research Unit, has been appointed to a national team of specialists addressing chronic wasting disease issues in the Southwest.
Kerry Mower, a wildlife disease specialist with the New Mexico Department of Game and Fish, said New Mexico is home to about 80,000 deer and 70,000 to 90,000 elk. The department annually licenses about 65,000 deer hunters who harvest 16,000 deer, he said. About 35,000 elk hunters receive licenses and harvest some 10,000 elk.
Boren emphasized that there is no scientific evidence the brain-wasting prion disease can spread to species other than deer or elk, but research in this area continues. Cattle living in pens near deer and elk infected with chronic wasting disease have shown no evidence of the disease after five years, said Elizabeth Williams, a professor of veterinary sciences at the University of Wyoming.
However, other researchers have found that under intensive laboratory conditions, chronic wasting disease was been transmitted to cattle by placing the disease protein directly into the cow's brain tissue.
Separately, some hunter- and tourism-dependent states are taking extremely aggressive steps to halt the spread of the disease. In Wisconsin, authorities have set out to kill 25,000 deer in a 360-square-mile area using teams of hired sharpshooters, after identifying just 24 deer with the disease.
© 2013 New Mexico State University Board of Regents
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