What is Chronic Wasting Disease (CWD)?

Chronic Wasting Disease (CWD) is a transmissible spongiform encephalopathy (TSE) of deer and elk. To date, this disease has been found only in cervids (members of the deer family) in North America. The disease affects the neurological system.

Within the family of transmissible spongiform encephalopathies (TSE), there are three predominant variants that affect animals: scrapie, which has been identified in sheep for more than 200 years; bovine spongiform encephalopathy (BSE) in cattle (sometimes referred to as “Mad Cow Disease”) and chronic wasting disease (CWD) in deer and elk. Within the family, there are also two main variants that affect humans: Creutzfeldt-Jakob Disease (CJD), which occurs naturally in one out of every one million people; and New Variant Creutzfeldt-Jakob Disease (nvCJD), which has been linked to the large-scale outbreak of bovine spongiform encephalopthy in cattle herds in Great Britain.

While the agent that produces CWD in deer and elk has not been positively identified, there is strong evidence to suggest that abnormally shaped proteins, called prions, are responsible. Research indicates that the prions accumulate only in certain parts of infected animals-the brain, eyes, spinal cord, lymph nodes, tonsils, spleen, bone marrow, the lining of the gut and to a lesser extent in blood and least of all in muscle meat. If the rule holds, that prions are produced massively in highly active tissues, then velvet deer antlers are primary candidates for CWD infectivity.

CWD is far less prevalent in elk than in deer. Less than 1 percent of elk in endemic areas have been found to be infected. Historical infection rates in deer herds vary from less than 1 percent to a range from 3 to 15 percent. The difference in infestation rates may be attributed to the social nature of deer.

What Are Signs of this Disease in deer?

Most cases of CWD occur in adult animals. The disease is progressive and always fatal. The most obvious and consistent sign of CWD is weight loss over time. Behavioral changes also occur in the majority of cases, including decreased interactions with other animals, listlessness, lowering of the head, blank facial expression, and repetitive walking in set patterns. In elk, behavioral changes may also include hyperexcitability, and nervousness. Affected animals continue to eat grain but may show decreased interest in hay. Excessive salivation and grinding of the teeth also are observed. Most deer show increased drinking and urination.

How is the disease spread?

The origin and mode of transition of CWD in unknown. Animals born in captivity and those born in the wild have been affected with the disease. Based on epidemiology, transmission of CWD is thought to be lateral or from animal to animal: although maternal transmission may occur, it appears to be relatively unimportant in maintaining epidemics. Experimental and circumstantial evidence suggests infected deer and elk probably transmit the disease through animal to animal contact and/or contamination of food or water sources with saliva, urine, and/or feces. CWD seems more likely to occur in areas where deer and elk are crowded or where they congregate at man-made feed and water stations. Artificial feeding of deer and elk may compound the problem.

Is CWD Transmissible to Humans?

According to experts and public health officials, there is no evidence that CWD can be transmitted to humans or to animals other than deer and elk. More studies are taking place to determine if this is a possibility.

In comparing the infection of humans with BSE and the possibility of infection from CWD we can look at the situation recently in England with the Mad Cow Disease outbreak. By comparing the consumer use of the BSE source (cattle) with the use of the source of CWD (deer and elk):

1. The geographical area with CWD is found in the USA is a tiny fraction of area in Great Britain (UK) contaminated with BSE.

2. The human population density in the US CWD area is very low compared to the population density in the UK.

3. Beef is a commercial staple in the UK. The British consumed nearly 750,00 infected cattle during a 10-year period, approximately 100 humans have died to date after contracting nvCJD. Venison is not a commercial staple in the US.

4. Beef brains in the UK went into sausages; deer brains do not.

5. Beef blood in the UK is used for blood pudding or blood and tongue sausage; deer blood normally stays in the field.

6. Lymph nodes in butchered beef go to processed meats; deer lymph nodes are cut out and thrown away.

7. Beef rumen and intestine may be eaten as tripe or sausage casings; American hunters do not eat the guts of the deer.

8. Beef bones are sold for stock (marrow very infected); deer bones are not frequently used for stock.

9. Where do cow udders go in a butchering plant? Here deer udders go to the dog or the dump.

Though there is talk of a “species barrier” for transmission it is not an absolute. The best hypothesis is that CWD arose from scrapie, a TSE found in sheep, a stable and for humans apparently not infective form of TSE. From sheep, CWD jumped to mule deer, then to elk, and then to whitetail.

How widespread is CWD?

The disease has been diagnosed in wild deer and elk in northeastern Colorado and southeastern Wyoming and in adjacent Nebraska. It has also been found in captive herd of elk in Colorado, Montana, Nebraska, Oklahoma, Kansas, South Dakota and the Canadian province of Saskatchewan.

The disease has also recently been found in wild deer in Wisconsin. This is significant because they are the first cases found east of the Mississippi.

What precautions should a person take?

In most of the United States and Canada there are virtually no special precautions that need to be taken because CWD is not present. Many of the following precautions can help in preventing infection by diseases that may be transmitted by deer or elk even if CWD is not present in your area. If the disease is noted in or near where an endemic infestation has occurred, the following precautions should be taken.

• Do not shoot, handle or consume any animal that appears sick. Contact your local Division of Wildlife and report the animal and the area it was located.
• Wear rubber gloves when field dressing carcasses.
• Wash hands and instruments thoroughly after field dressing is completed.
• De-bone the carcass using a knife only and discard bones and internal organs. Do not saw through bone marrow and back bone, spraying marrow and spinal cord on the meat.
• Minimize the handling of the brain and spinal tissues. Recommend taxidermists wear heavy vinyl work gloves or heavy rubber gloves when sawing through the skullcap. Tools used in preparation of the skull plate should be sterilized in appropriate solutions after being scrubbed with strong detergent. The skull plates should be cleaned by methods that do not splash or spread the material or the solutions
• Avoid consuming brain, spinal cord, eyes, spleen, tonsils and lymph nodes of harvested animals. (Normal field dressing coupled with boning out a carcass will remove most, if not all, of these body parts. Cutting away all fatty tissue will remove remaining lymph nodes.)
• Avoid consuming the meat from any animal that tests positive for the disease.
• Request that your animal is processed individually, without meat from other animals being added to meat from your animal.

Sources

     1. Colorado Division of Wildlife

     2. United States Department of Agriculture

     3. The Milwaukee Journal Sentinel

     4. Val Geist, Professor Emeritus of Environmental Science at the University of Calgary