Chronic wasting disease (CWD) is a fatal disease affecting deer and elk in North America (as yet). It is categorized as a transmissible spongiform encephalopathy (TSE), making it similar in nature to the infamous and feared bovine spongiform encephalopathy (BSE, known colloquially as "mad cow disease") and Creutzfeldt-Jakob disease (CJD).
TSEs are degenerative brain diseases that are thought to be caused by prions (an abnormal form of protein) that are able to change other proteins into abnormal ones. They then begin to accumulate in the brain and lymphoid tissue, creating microscopic holes in the tissue (where "spongiform" comes from, describing the appearance of the affected brain). While this has yet to be conclusively proven, most evidence points toward this as the causative agent.
Other TSEs include:
TSEs in humans
- Creutzfeldt-Jakob disease (CJD): First described in 1921. That is the "classic" (sporadic CJD or spCJD) variant of the disease.
Other variants include:
- variant CJD (vCJD): Related to BSE. First diagnosed in 1996, the first case reported symptoms in 1994.
- genetic CJD (gCJD): An inherited form of the disease.
- iatrogenic CJD (iCJD): CJD acquired from medical accident.
- Fatal familial insomnia (FFI): Genetic disease which includes the severe inability to sleep along with the other symptoms of CJD.
- Gerstmann-Sträussler-Scheinker disease (GSS; sometimes "syndrome"): Another genetic form that usually takes much longer to develop.
- Kuru: Found in members of New Guinea tribes who practiced some cannibalism (in particular, the infected brain).
It should be noted that all human forms of TSEs are very rare.
While CWD is similar in many respects to the other TSEs, it should not be mistaken as any of them. It is unique form of TSE.
Named for the most obvious physical characteristic of the disease, deer and elk affected by CWD are unable to maintain a healthy weight and suffer from catastrophic weight loss. The degeneration of the brain also makes them act confused or listlessness (it has been described as looking drunk). They also exhibit less interaction with other deer, lowering of the head, walking in repetitive patterns, and even grinding of the teeth. It can also cause other behavioral changes, including excitability or anxiety/nervousness. Other symptoms include excess salivation and frequent urination (which leads to increased water consumption). It is not uncommon to be accompanied by pneumonia (occasionally, few symptoms aside from the pneumonia will show; this is rare).
Symptoms can last either weeks or months before death takes place. Most animals are about three or four years of age before symptoms occur but it has been observed in ones as young as 18 months and as old as 13 years.
There is no known treatment of any kind. CWD is always fatal.
It is currently unknown how CWD originated or how it is transmitted. All evidence shows that deer and elk in close association (the majority of the cases have been on farms and ranchesthough it may be just as common in the wild) tend spread CWD. It had also been found that the "environment" where the animals reside can retain the causative agent, as uninfected animals have gotten it when placed in areas where infected ones had once lived.
The best hypothesis seems to be that the spread is due to bodily fluids (waste products and saliva), which would also explain why the environment would remain "infected." There is also evidence that it can be passed from mother to youngthough it could still be a result of "external" agents, given the proximity of the young to the mother.
As yet, there is no evidence that CWD can "jump" the barrier from deer/elk to other species. Sheep, cattle, and goats have all been kept with infected animals and none have developed CWD. In another study wherein cattle had CWD directly injected into the brain, only three of thirteen developed the disease.
There is no live test for CWD, as the current method of identifying it involves examining the brain stem. This means that testing can only be used for surveillance purposes. A live test is being developed that uses the tonsils instead of the brain, but even if successful, it would be impractical to use with wild animals.
Danger to humans
While there is no evidence that CWD poses a danger to humans, hunters and anyone raising or caring for deer or elk are warned to be careful during handling (especially hunters):
- Obviously sick animals exhibiting the symptoms should not be taken and reported to the State Department of Natural Resources or other authorities.
- Rubber or latex gloves should be worn when field dressing the animal. Thorough handwashing should be done following the handling of any raw meat.
- The brain, spinal cord, and spleen should not be eaten.
- The meat should be boned out and the brain, eyes, lymph nodes, spinal cord, and spleen should all be discarded (preferably in doubled plastic garbage bags and disposed of at a landfill where there are facilities for such disposal).
- Tools used for cutting during dressing should not be household utensils and should be well disinfected following use (chlorine bleach is recommended).
- Avoid cutting into the brain or spinal cord if at all possible. If it occurs, the tool should not be used on other parts of the animal.
As noted, there is currently zero evidence suggesting that CWD is a threat to humans who eat venison. This does not mean it will continue to be or that one may ignore the possibility. Most experts say the meat is safe and if the proper precautions are taken, should remain so.
The occurrence of CWD in Wisconsin has affected some of the traditional practices of Indian tribes there. It is still tradition to use the brains of the deer to aid the tanning of a deer hide (reportedly the best substance for the job). Now they must wear gloves and in some cases protective clothing. Some tribal councils have also ceased serving venison.
CWD was first identified (as a set of symptoms resulting in the death of the animal) in mule deer in 1967 at a wildlife research facility in northern Colorado. Not long after, the same was observed at a Wyoming facility. This wasn't immediately alarming because they were captive animals and both facilities traded animals back and forth. Between 1974 and 1979, of 67 animals (66 mule deer, one black-tailed deer) at the two facilities, 57 got CWD. All died.
It wasn't until 1978 that it was identified as a TSE. The first wild deer and elk with the disease began to appear in 1981 (still in Colorado). The first appearance of wild victims in Wyoming came in 1985 (by 2001, it was estimated as many as 10% of Wyoming deer had CWD). It continued to spread, including the states of South Dakota (1997), Nebraska (1998), Oklahoma (1998), Montana (1999), Kansas (2001), Wisconsin (2002, from animals harvested during the 2001 season), New Mexico (2002), and Minnesota (2002). With the exceptions of Wisconsin and New Mexico, these were all farmed deer or elk.
Appearences in the wild took longer to occur or simply took longer to be found by researchers. A wild deer with CWD in Nebraska wasn't found until 2000 with South Dakota following two years later. More are expected to be found in the wild and the disease has continues to pop up sporadically in other deer or elk farms. Measures have been taken to study the problem and attempts to control the spread by culling deer suspected of infection. Quarantining of animals is also used. Bans on feeding wild deer have also been considered.
CWD is not confined to the US (though it most likely originated there). Canada had a case as early as the 1970s, the victim being a mule deer at a zoo that had been imported from Colorado. The first occurrence outside of that was in Saskatchewan in 1996. Since then, 39 game ranches there and one in Alberta have found cases (the first wild example was in Saskatchewan in 2001). Infected elk seem to be more of a problem than deer at this time.
Similar measures to those in the US are being used to identify and control the problem. Canada has also prohibited any products that come from known infected deer or elk to enter the human or animal food chain (elk antler velvet is sometimes used in alternative medicine) and strictly monitors the import of any deer or elk (there was an import ban for those animals from the US between 1990 and 1999).
It is almost unquestionably the case that CWD will continue to spread into deer and elk populations in other states (and probably provinces, as well), making awareness and monitoring very importantespecially if it ever does jump the barrier to other species.
(Sources: www.aphis.usda.gov/oa/pubs/qacwd.html, www.aphis.usda.gov/oa/pubs/fscwd.html, www.ngpc.state.ne.us/wildlife/cwd/cwdgeneral.html, www.wildlifedepartment.com/cwd.htm, www.inspection.gc.ca/english/anima/heasan/disemala/cwdmdce.shtml, www3.gov.ab.ca/srd/fw/diseases/pdf/CWDFACT.pdf, www.huntfishcampwisconsin.com/CWDTimeline.html)