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What is Chronic Wasting Disease?
Chronic Wasting Disease (CWD) appears to be a prion disease that attacks the central nervous system and causes fatal damage to the brain of white-tailed deer, mule deer, and Rocky Mountain elk. CWD is similar to, but significantly different from, scrapie (documented in domestic sheep for over 400 years), Bovine Spongiform Encephalopathy (BSE and often referred to as mad cow disease) and variant Creutzfeldt-Jakob disease (vCJD), and Creutzfeldt-Jakob disease (CJD). CJD and vCJD are the only nonhereditary prion diseases found in humans. All of these diseases attack the central nervous system and cause small holes to form in the brains of infected animals.
What Are the Symptoms?
In the later stages of infection, deer and elk infected with CWD will show signs of progressive weight loss, listlessness, excessive salivation and urination, increased water intake, depression and, eventually, death. Animals can be infected with CWD for months or years before outward signs of infection are evident. These symptoms are also found when an animal is infected with other diseases.
What Causes CWD?
The exact cause of CWD is not known at this time but the best scientific minds in the country feel that it is a prion disease. A prion is a mutated protein in the body that causes other normal proteins to fold abnormally and cause sponge-like holes in the brain. A growing body of research evidence indicates that this prion is the causative agent for CWD. The origin and life cycle of these prions are the target of ongoing research aimed at ultimately developing a management plan to eliminate, or at least contain, the existence of these prions in both wild and captive herds, as well as in the environment.
How Is It Transmitted Between Animals?
Although the exact method of transmission is unknown, it is known that CWD is transmitted from animal to animal. In all probability, the transmission is through body fluids like feces, urine, or saliva. Animals that are crowded or confined have a greater chance of encountering the body fluids of other animals and, therefore, a higher likelihood of becoming infected if the rogue prion is present. Animals that have a social system that includes close contact with herd mates also have a higher chance of becoming infected. Recent research indicates that CWD prions can survive in the environment after infected and exposed animals are removed.
Where Does CWD Occur?
CWD is a disease unique to North America. On our continent, it has been found in wild deer and/or elk in Colorado, Wyoming, Nebraska, South Dakota, Wisconsin, Utah, New Mexico, Illinois, New York, West Virginia and Alberta and Saskatchewan, Canada. In captive deer and or elk, it has been found in Colorado, Montana, South Dakota, Oklahoma, Kansas, Nebraska, Wisconsin, Minnesota, New York, Saskatchewan, and Alberta. Captive operations in Cherry County, Cheyenne County, and Sioux County Nebraska have had elk test positive.
In the wild, CWD has been found in both mule deer and white-tailed deer. Free-roaming deer from Kimball, Cheyenne, Scottsbluff, Morrill, Banner, Box Butte, Dawes, Sheridan, Arthur, Hall, Keith, Red Willow and Sioux Counties have tested positive for the disease.
How are Animals Tested for CWD?
Currently, the acceptable tests require a microscopic examination of an animal's brain stem, retropharyngeal lymph node, or tonsil. For the brain stem or lymph node tests, the animal must be dead. The tonsil test only works on deer, not elk. Tonsil tests are not practical to use on wild animals as they must be tranquilized and held in captivity until results are known. The screening test for CWD is the ELISA test and takes two to three days; confirmation tests (IHC) require a much longer time to validate the initial finding.
Can Humans Be Infected with CWD?
There is currently no scientific evidence that CWD has or can spread to humans, either through contact with infected animals or by eating the meat of infected animals. The Centers for Disease Control and Prevention 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, the Commission recommends 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 the Commission. Avoid cutting or puncturing the spinal cords or brains of animals taken in the areas where CWD occurs. Do not use household utensils to field dress or process your deer. Wear rubber or latex gloves when handling any harvested animal.
Can the Disease Spread to Other Animals, Such As Cattle?
Again, there is no indication or scientific evidence that the disease can spread to species other than deer or elk, but research in this area continues. Studies have shown that cattle placed in close and confined proximity with infected deer and elk have not developed the disease after living with them for over seven years.
How Common Is the Disease?
As more extensive steps have been taken to learn more about the disease, its spread, and its prevalence in both wild and captive deer and elk herds, the body of evidence continues to grow. It was once thought that the disease occurs naturally in less than 5 percent of the wild deer population and in about 1 percent of the wild elk population, largely based on studies conducted in the infected areas of Colorado and Wyoming. More recently, however, concern has increased that perhaps those numbers may be greater, particularly in the more socially oriented white-tailed deer populations.
Additionally, recent research indicates that there may be pockets of infection with very high rates of the CWD within the larger endemic area. Also, mature bucks appear to be infected at a higher rate than other portions of the population. Prevalence in the endemic area of Nebraska is generally less than 1 percent. However, there are portions of the Panhandle that approach 2 percent. No wild elk in Nebraska have tested positive for the disease. The Commission has tested over 33,000 deer from 1997 to 2007 with 133 deer testing positive for the disease.
What Action is the Commission Taking?
The Commission is currently supporting research to determine the impact of social behavior and movements on the spread of the disease. It will continue its surveillance program to track prevalence and distribution of CWD to provide hunters with this information. Commission staff cooperates with other state/federal agencies in information sharing and programs aimed at further understanding the disease.