What is Chronic Wasting Disease?

CWD is known to infect cervids (deer and elk). The causative agent of the disease is thought to be a prion. Prions are unlike viruses and bacteria in that they have no genetic material. Prions are abnormal proteins that infect the host animal by promoting the conversion of normal cellular prion proteins to an abnormal form. This generation of abnormal proteins causes degeneration of brain tissue, creating a sponge-like appearance.

CWD was first discovered in Colorado in 1967, and was classified as a TSE in 1978. Chronic wasting disease generally occurs in adult animals. There is no treatment for CWD, no vaccine for prevention, and no documented immunity to the disease in deer.

Symptoms of CWD

A list of CWD symptoms in deer include:

Where is CWD?

The disease has been found in free-ranging and captive cervids. CWD has been found in free ranging cervids in Wisconsin, Wyoming, Colorado, Nebraska, Illinois, South Dakota, New Mexico and Saskatchewan, Canada. Cases have also been found in captive cervids in Wisconsin, South Dakota, Oklahoma, Kansas, Nebraska, Colorado, Montana, Minnesota and Saskatchewan, Canada.

Do all deer in CWD areas have the disease?

No, most endemic areas have a prevalence of 1 to 5%, with some areas having prevalence in excess of 20%.

Transmission of CWD

The exact mode of transmission is still unknown. Circumstantial and experimental information indicated that the disease is spread laterally, either by animal-to-animal contact, or by environmental contamination. Routes of transmission are presumed to be exposure to saliva, urine, feces and placental tissue. Prions have been found in nervous system tissue and lymphatic tissue, but have not been found in muscle tissue.

Testing for CWD

Testing for CWD is a difficult and time-consuming process. Conventional testing requires the extraction of the deer’s brain stem (obex). The brain stem is then tested for abnormal prion proteins using a technique called immuno-histo-chemistry. The IHC is a postmortem test, meaning the animal must be killed to extract the necessary brain tissue. IHC tests require technical equipment and skilled technicians. There are few labs in the nation certified; therefore testing facilities are overloaded with samples. It may take 3-6 months to obtain results from IHC testing. The western blot technique utilizes lymphatic tissue from the animal to test for abnormal prion proteins. This test has 95% accuracy and produces results in less than a week. It has now been found that it is able to discover CWD prions at earlier stages than IHC. This test is typically used in conjunction with the IHC. Currently, there is great demand for a live test for CWD for the farmed cervid industry and a quick field test for CWD hunters. MDHA is currently working with the MN DRN, University of Minnesota Veterinary Diagnostic Lab and the USDA investigation the potential of providing CWD testing for hunters who wish to test their deer.

Human Health

There has not been a case of CWD transmission to livestock, predators or humans in 17 years of monitoring and investigation. The human equivalent of the disease is Creutzfeld-Jacobs disease (CJD). Each year, one out of every million people contract CJD, hunters and non-hunters alike.

CJD cases have been present in North America long before the discovery of CWD. There are no more CJD cases in humans than are expected, even in those states with CWD.

The World Health Organization (WHO) has said there is no scientific evidence CWD can infect humans. However, as a general precaution, WHO also recommends no part of a deer or elk with evidence of CWD be eaten by people or fed to other animals. Over 17 years of monitoring the infected area in Colorado has found no abnormal diseases in people, cattle, or predators living there.

Precautions

These are precautions that can be taken in areas known to have CWD present:

• Wear latex/rubber gloves while field dressing and processing cervids
• De-bone and remove all fatty tissue from meat
• Minimize contact with nervous system tissue (spinal cord, brain, etc)
• Do not eat the brain, spinal cord, eyes, spleen, tonsils, or lymph nodes
• Use only a knife to butcher your deer, avoid cutting and sawing bone material, especially the spine
• Do not consume animals that appear unhealthy
• Wash hands and instruments thoroughly after field dressing and meat processing

* The CWD prion is not known to be in the meat itself.

Websites for further information on CWD

• CWD Alliance: www.cwd-infor.org
• MN DNR: www.dnr.state.mn.us
• Wisconsin DNR: www.dnr.state.wi.us
• BAH: www.bah.state.mn.us
• MN Dept. of Agrigulture: www.mda.state.mn.us
• USDA APHIS: www.aphis.usda.gov
• U of MN: www.cvm.umn.edu
• U of Wyoming Veterinary Lab: www.wyovet.edu/WSVL/cwd.html