Chronic wasting disease
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2008-07-14T18:07:21Z
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'''Chronic wasting disease''' (CWD) is a [[transmissible spongiform encephalopathy]] (TSE) of [[deer]], [[elk]] (wapiti), and [[moose]]. TSEs are caused by unusual [[infectious disease|infectious agents]] known as [[prion]]s. To date, CWD has been found mainly in [[cervid]]s (members of the deer family). First recognized as a clinical "wasting" syndrome in [[1967]] in [[mule deer]] in a wildlife research facility in northern [[Colorado]], it was identified as a TSE in [[1978]] and has spread to a dozen states and two Canadian provinces.<ref name="Blakeslee">
{{cite news
| url = http://www.nytimes.com/2005/10/04/science/04tong.html
| title = Wasting-Disease Culprit May Be Tongue
| accessdate = 2008-04-08
| last = Blakeslee
| first = Sandra
| date = 2005-10-04
| publisher = [[The New York Times]]
| quote = Since it was first identified two decades ago in deer in Colorado, chronic wasting disease has spread to a dozen states (including New York) and two Canadian provinces.
}}</ref> CWD is typified by chronic weight loss leading to death. There is no known relationship between CWD and any other TSE of animals or people. Although there have been reports in the popular press of humans being affected by CWD, a study by the [[Centers for Disease Control and Prevention|CDC]] failed to find any relationship.<ref>
{{cite journal
| last = Belay
| first = E.D.
| coauthors = Maddox, R.A.; Williams, E.S.; Miller, M.W.; Gambetti, P.; Schonberger, L.B.
| year = 2004
| month = June
| title = Chronic Wasting Disease and Potential Transmission to Humans
| journal = Emerging Infectious Diseases
| volume = 10
| issue = 6
| pages = 977–984
| publisher = [[Centers for Disease Control and Prevention|CDC]]
| url = http://www.cdc.gov/ncidod/EID/vol10no6/03-1082.htm
| accessdate = 2008-04-08
}}</ref>
== Clinical signs ==
Most cases of CWD occur in adult animals. The disease is progressive and always fatal. The most obvious and consistent clinical 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.
== Causative agent ==
The agent responsible for CWD (and other TSEs, such as [[scrapie]] and [[bovine spongiform encephalopathy]]) is a [[prion]], an abnormal form of a normal [[protein]], known as prion protein (PrP), most commonly found in the [[central nervous system]] (CNS), and is capable of spreading to the [[peripheral nervous system]] (PNS), thus infecting meat, or muscle, of deer and elk. The abnormal prion protein infects the host animal by promoting conversion of normal cellular prion protein (PrP<sup>C</sup>) to the abnormal prion form (PrP<sup>CWD</sup>). The build-up of PrP<sup>CWD</sup> in the brain is associated with widespread [[neurodegenerative disease|neurodegeneration]].
== Diagnosis ==
Research is being conducted to develop live-animal diagnostic tests for CWD. Currently, definitive diagnosis is based on postmortem examination ([[necropsy]]) and testing. Gross lesions seen at necropsy reflect the clinical signs of CWD, primarily emaciation. [[Aspiration pneumonia]], which may be the actual cause of death, also is a common finding in animals affected with CWD. On microscopic examination, lesions of CWD in the central nervous system resemble those of other TSEs. In addition, scientists use a technique called [[immunohistochemistry]] to test [[brain]] tissue for the presence of the abnormal prion protein to diagnose CWD.
== Epidemiology ==
The origin and mode of transmission of the prions causing CWD is unknown, but recent research indicates that prions can be excreted by deer and elk, and is transmitted by eating grass growing in contaminated soil.<ref>{{cite web | date = [[September 17]] [[2003]] | url = http://www.sciencedaily.com/releases/2003/09/030917074003.htm | title = Study Shows Prions Stick Around In Certain Soils | publisher = Science Daily | accessmonthday = October 23 | accessyear = 2006}}</ref><ref>{{cite web | date = [[May 19]] [[2004]] | url = http://www.sciencedaily.com/releases/2004/05/040519065431.htm | title = New Research Supports Theory That Indirect Transmission Of Chronic Wasting Disease Possible In Mule Deer | publisher = Science Daily | accessmonthday = October 23 | accessyear = 2006}}</ref> 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. Research has recently shown that an infected deer's saliva is able to spread the CWD prions.<ref>{{cite journal | first = CK | last = Mathiason | coauthors = Powers JG, Dahmes SJ, Osborn DA, Miller KV, Warren RJ, Mason GL, Hays SA, Hayes-Klug J, Seelig DM, Wild MA, Wolfe LL, Spraker TR, Miller MW, Sigurdson CJ, Telling GC, Hoover EA | year = 2006 | month = October 6 | title = Infectious prions in the saliva and blood of deer with chronic wasting disease | journal = Science | volume = 314 | issue = 5796 | pages = 133–6 | pmid = 17023660 | accessdate = 2006-10-23 | doi = 10.1126/science.1132661}}</ref>
In the mid-1980s, CWD was detected in free-ranging deer and elk in contiguous portions of northeastern Colorado and southeastern [[Wyoming]]. Soon after diagnosis of the disease as a TSE, Colorado and Wyoming wildlife management agencies stopped the movement of deer and elk from their research facilities; wild cervids have not been translocated from the endemic area. In May [[2001]], CWD was also found in free-ranging deer in the southwestern corner of [[Nebraska]] (adjacent to Colorado and Wyoming) and later in additional areas in western Nebraska. The limited area of northern Colorado, southern Wyoming, and western Nebraska in which free-ranging deer, moose, and/or elk positive for CWD have been found is referred to as the [[endemic (epidemiology)|endemic]] area. The area in [[2006]] has expanded to six states including parts of eastern [[Utah]], southwestern [[South Dakota]], and northeastern [[Kansas]]. There are also non-contigious (to the endemic area) areas in central Utah and central Nebraska. The limits of the affected areas are not well defined since the disease is at a low incidence and the amount of sampling may not be adequate to detect it. In [[2002]], CWD was detected in wild deer in south-central [[Wisconsin]] and northern [[Illinois]] and in an isolated area of southern [[New Mexico]]. In [[2005]], it was found in wild [[White-tailed deer]] in [[New York]] and [[West Virginia]]. It is also found in the Canadian provinces of [[Alberta]] and [[Saskatchewan]]. [[Image:Chronic wasting disease aug 2006.jpg|right|300px|thumb|Chronic wasting disease in North America]]
CWD also has been diagnosed in farmed elk and deer herds in a number of States and in two [[Canada|Canadian]] provinces. The first positive farmed elk herd in the [[United States]] was detected in [[1997]] in [[South Dakota]].
Since then, additional positive elk herds and farmed [[White-tailed deer]] herds have been found in South Dakota (7), Nebraska (4), Colorado (10), [[Oklahoma]] (1), Kansas (1), [[Minnesota]] (3), [[Montana]] (1), Wisconsin (6) and [[New York]] (2). As of fall of 2006, four positive elk herds in Colorado and a positive White-tailed deer herd in Wisconsin remain under State [[quarantine]]. All of the other herds have been depopulated or have been slaughtered and tested, and the quarantine has been lifted from one herd that underwent rigorous surveillance with no further evidence of disease. CWD also has been found in farmed elk in the Canadian provinces of [[Saskatchewan]] and [[Alberta]]. A retrospective study also showed that Mule deer exported from [[Denver]] to the [[Toronto Zoo]] in the 1980s were affected.
Species that have been affected with CWD include [[elk]], [[mule deer]], [[white-tailed deer]], [[black-tailed deer]], and [[moose]]. Other [[ruminant]] species, including wild ruminants and domestic [[cattle]], [[sheep]], and [[goat]]s, have been housed in wildlife facilities in direct or indirect contact with CWD-affected deer and elk with no evidence of disease transmission. There is ongoing research to further explore the possibility of transmission of CWD to other species.
== References ==
{{reflist}}
== External links ==
* *''This entry incorporates public domain text originally from the [http://www.aphis.usda.gov/vs/nahps/cwd/ Animal and Plant Health Inspection Service], [[APHIS]].''
* [http://www.cwd-info.org/ Chronic Wasting Disease Alliance]
* {{cite web | year = 2006-10-03 | url = http://www.inspection.gc.ca/english/anima/heasan/disemala/cwdmdc/cwdmdce.shtml | title = Chronic Wasting Disease (CWD) of Deer and Elk | publisher = Canadian Food Inspection Agency | accessmonthday = October 23 | accessyear = 2006}}
* [http://www.elkresearch.org/ Elk Research Institute]
* [http://www.nwhc.usgs.gov/disease_information/chronic_wasting_disease/index.jsp United States Geological Survey]
* [http://www.aphis.usda.gov/vs/nahps/cwd/ United States Department of Agriculture]
* [http://wildlife.state.co.us/Hunting/BigGame/CWD/ Colorado Division of Wildlife]
* [http://dnr.state.il.us/CWD/ Illinois Department of Natural Resources]
* [http://www.dnr.state.mn.us/mammals/deer/cwd/index.html Minnesota Department of Natural Resources]
* [http://www.ngpc.state.ne.us/wildlife/guides/cwd/cwd.asp Nebraska Game and Parks Commission]
* [http://www.dec.state.ny.us/website/dfwmr/wildlife/deer/cwd.html New York State Department of Environmental Conservation]
* [http://www.dnr.state.wi.us/org/land/wildlife/whealth/issues/CWD/ Wisconsin Department of Natural Resources]
* [http://gf.state.wy.us/services/education/cwd/index.asp Wyoming Game and Fish]
* [http://wildlifedisease.nbii.gov/diseasehome.jsp?disease=Chronic%20Wasting%20Disease&pagemode=submit Wildlife Disease Information Node Chronic Wasting Disease Factsheet and resources]
{{Prion diseases}}
[[Category:Neurology]]
[[Category:Prions]]
[[Category:Transmissible spongiform encephalopathies]]
[[Category:Animal diseases]]
[[fr:Chronic Wasting Disease]]
[[it:Malattia del deperimento cronico del cervo]]
[[ja:慢性消耗病]]
[[pl:Przewlekła choroba wyniszczająca]]