Update on CWD in Alberta

Last Review/Updated: March 10, 2009

Chronic Wasting Disease

Name of Condition

Chronic Wasting Disease (CWD), prion disease of cervids, cervid spongiform encephalopathy.

Name of Agent

An unnamed prion protein.

Significance

CWD has the potential to infect and cause mortality in a variety of cervids [members of the deer family]. In Canada, CWD has become widespread in mule deer, white-tailed deer, and a few elk in Saskatchewan and has spilled over into deer in areas in Alberta adjacent to the Saskatchewan border. In the USA, infections are known in wild mule deer, elk, white-tailed deer, and a few moose in a core area of the western USA, a focus of CWD in wild white-tailed deer along the Wisconsin/Illinois border, and isolated reports of CWD in wild deer in a few other states. The disease has been found in game farm elk and white-tailed deer in the US (various states) and Canada (Saskatchewan, Alberta), as well as translocated farmed elk in South Korea.

Background

Although identified in the 1970s and 1980s, CWD probably occurred in a localized area of Colorado/ Wyoming/ Nebraska for quite some time. It may be the result of local transformation of a prion agent that causes scrapie in domestic sheep. However, CWD is known to occur only in cervids, and is not a disease of traditional livestock (cows, sheep or pigs). Infected deer and elk cannot maintain weight and slowly waste away. Excessive salivation as well as lethargy, incoordination, and drooping head and ears also are common in individual animals that show clinical signs. Infection appears to be fatal in all cases.

The nervous system is the preferred habitat for the agent of CWD. Infections are associated with clear open spaces within the animal's brain tissue that make it look somewhat like a sponge. Needless to say, these spaces result in changes to behaviour, attitude, and metabolism that lead to the clinical signs described above.

Transmission Dynamics

To date, we do not know the specific mechanisms of transmission of CWD. The disease can pass from one individual animal to another and occasionally passes from females to their offspring. Infectious material can survive also in heavily contaminated environments for an unknown period of time. The disease can be passed to new individuals via experimental transfer of body fluids but their role and importance in transmitting CWD among wild cervids has not yet been determined. Other than young fawns, infections have been found in males and females of all ages, although adult males have a higher rate of infection.

Threshold events in Alberta's CWD History

In response to the first finding of CWD in a wild mule deer in Saskatchewan early in 2001, the Fish and Wildlife Division collected wild deer along the Alberta/Saskatchewan border in April 2001. All deer collected were negative for CWD.

In late March 2002, CWD was identified in a farmed elk in Alberta. The infection was detected during the provincial surveillance program that began in 1996. Federal CWD eradication programs were implemented immediately. All farmed cervids that moved on or off the premises in the previous three years as well as the current animals on the farm were killed and tested. No further CWD was found.

In early November 2002, CWD was identified in two farmed white-tailed deer on one farm in Alberta. As with the farmed elk, federal control and eradication programs were implemented immediately. No further cases of CWD were found. In response to finding CWD on two game farms in central Alberta, the Fish and Wildlife Division sampled wild deer in the vicinity of the farms in late February/early March 2003. All deer and elk collected were negative for CWD. Ongoing hunter surveillance in the area from fall 2002 to fall 2005 did not detect any evidence of CWD in wild deer.

In late March/April 2005, the Fish and Wildlife Division collected deer from a small high risk area east of Chauvin near the Alberta-Saskatchewan border. (CWD was known to occur in wild deer in the adjacent area of Saskatchewan). The program was designed to enhance the surveillance sample in this area and initiate reduction of the local deer density. All deer collected were negative for CWD.

On September 2, 2005, CWD was confirmed in an emaciated mule deer found in a farmyard about 30 kilometres southeast of Oyen, Alberta. This was the first wild deer found to have the disease in Alberta.

Since 2005, Alberta has delivered an aggressive program to find and remove infected wild deer and to limit spread of the disease. The program relies heavily on hunters and landowners as well as extensive public information provided on an ongoing basis. Additional cases of CWD are listed below under "Updates."

Importance for Wildlife Management

Chronic wasting disease is considered a relatively recent occurrence in wild cervids in North America and there is no evidence that it is a component of native ecosystems. As such, the full effects of the disease in wild populations cannot yet be determined. Within affected jurisdictions the disease generally is not widespread and often occurs in local adjacent deer populations. Mortality does not seem to affect overall productivity in infected populations in the short term, although models applied to data collected in Colorado, and more recently in Wisconsin, suggest that deer populations at the heart of an affected area decline and disappear over the long term. Infected populations in the core areas of the western US, where CWD has been present for a few decades, have a lower proportion of older-aged deer, and particularly fewer older adult males. Infected females die prematurely and do not provide their full potential to the ongoing productivity of the population, that is, the fawns that would have been produced in later years are not available if the doe dies prematurely of CWD. As the prevalence of CWD increases over time in local populations, these effects are more pronounced.

The finding of CWD in wild and farmed white-tailed deer in the eastern US, particularly Wisconsin and Illinois, causes significant concern for wildlife managers in the east. The high density of wild deer (in the range of 75-100 white-tails/mi2) and high number of game farms in eastern regions provide added risk of transmission. More information is needed before all the risks can be properly assessed. Many jurisdictions have developed new restrictions on the intra- and inter-jurisdictional movement of farmed cervids and wild cervid parts in an attempt to limit potential spread of CWD. A list of state and provincial regulations and/or policies are available.

A related concern about CWD is the potential for misrepresenting it as being equivalent to bovine spongiform encephalopathy (BSE), the infamous "mad cow disease," a prion disease of bovids (cattle). BSE has been associated with a similar prion infection in humans, variant Creutzfeldt-Jakob disease, and poses worldwide concern for public health and agricultural economics. However, CWD and BSE are not the same.

Based largely on the perceived human health concerns, wildlife managers throughout Canada and the US expend considerable time, effort, and monies on surveillance programs aimed at defining exactly where CWD occurs or does not occur in the wild. A map of current distributions of CWD in North America is maintained by the CWD Alliance.

Alberta began surveillance of wild deer and elk for CWD in 1996. Submission of heads of hunter-killed animals is the primary source of surveillance samples, supplemented with testing of clinical suspects (deer that display behaviour or body condition consistent with possible CWD infection). Particular emphasis is placed in testing heads of deer killed in the areas at risk for CWD along the Alberta/ Saskatchewan border, although the program accepts heads from deer or elk killed anywhere in Alberta. Over 30,000 heads of wild deer and elk have been tested since the program began. Please see the CWD Surveillance Program in Alberta page for general information and summary surveillance results from farmed and wild cervids in Alberta. Information regarding CWD-infected wild deer in Alberta is available in the "UPDATES" below.

There are numerous research projects underway to better define the host range, method of transmission, diagnostic tests, impact on wild cervids, and risk to the public and livestock.

Public Significance

This disease poses significant economic concerns for farmers of elk and deer. In the 1980s, CWD was introduced into captive (=farmed) elk populations via live wild elk taken from affected areas in the US. It was then unintentionally translocated to farms in various states as well as to Saskatchewan and Korea. Three cases also were documented in farmed cervids in Alberta. As a result, the economics of trade in live elk and their products (primarily antler velvet) have been seriously affected. Also, the association with BSE has led to possible public health concerns.

To date there is no scientific evidence to suggest that CWD can infect humans and growing evidence that the prion is indeed quite different from BSE. The US Centres for Disease Control advise that the human health risks from CWD, if any exist, are extremely low. However, as a precaution, the World Health Organization (WHO) recommends that all products from animals known to be infected with any prion disease should be excluded from the human food chain.

Prevention/Control

CWD is a federal reportable disease in Canada and appropriate surveillance and control programs for farmed cervids are underway. The procedures parallel those used to control and eradicate other federal reportable diseases and include

  • ongoing surveillance (testing of slaughtered animals, report of clinical signs),
  • quarantine of suspect and confirmed affected premises,
  • detailed traceouts from all known affected premises,
  • destruction of infected herds, and
  • compensation of owners of infected elk or deer.

Affected premises are thoroughly cleaned and disinfected before they can be restocked. Similar programs are underway in the US.

In addition, Alberta has stringent programs developed cooperatively among government agencies, game farmers, and other stakeholders to continually search for evidence of CWD in farmed and wild cervids as well as limit the possibility of introducing infections through animals imported into the province.

Summary

In Alberta, CWD has been identified in one farmed elk and two farmed white-tailed deer, and increasing numbers of wild mule deer and white-tailed deer near the Saskatchewan border. It is a serious disease concern for wildlife managers and an economic concern relative to the potential effects on recreation, tourism, and agriculture in Alberta. The province is committed to limiting the spread of CWD in wild cervid populations. Strict programs are in place to provide continual surveillance.

Additional information concerning CWD programs and surveillance data in Alberta is available at:

http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex3594 - Alberta Agriculture, Food and Rural Development

Chronic Wasting Disease (CWD) test results in Farmed and Wild Cervids in Alberta

CWD Alliance - for updates on this wildlife disease across North America (external site)

http://www.environment.gov.sk.ca/Default.aspx?DN=ff4336ff-98fe-43a1-98d0-8608c8aca619 -- for information on CWD in Saskatchewan

http://www.ccwhc.ca/Publications/NCWDCS2005.pdf -- Canada's National Chronic Wasting Disease Control Strategy

Publications

Reports and News Items

News Releases

CWD Workshop: Wildlife Agency Responses across North America

Updates

Chronic Wasting Disease: Surveillance Update: March 9, 2009

Alberta Sustainable Resource Development has completed testing all of the heads received to date from the chronic wasting disease (CWD) 2008 fall hunter surveillance:

  • A total of 8 new cases of CWD were identified in 4,347 heads tested since September 1, 2008.

  • Seven of the cases were hunter-harvested deer, the remaining CWD-positive deer was a road-kill collected by Fish and Wildlife staff.

  • The new cases are generally in the area of previous cases of CWD, although two infected deer found in Canadian Forces Base Wainwright are the farthest west the disease has been detected to date in Alberta.

  • Map: Chronic Wasting Disease in Wild Deer in Alberta (2005-2008)

  • Statistics: CWD in Wild Deer (2005-2008)

Notification of negative results

Individual hunters were notified of negative results through the Alberta Relm website and by letters sent in the mail. For more information, visit:

Any hunter who harvested a CWD-positive deer received a phone call directly from Fish and Wildlife staff.

Attention Hunters! If you still have frozen deer heads that you would like to submit to the ongoing CWD surveillance program, please drop them off at any Fish and Wildlife office during regular office hours.


Updated: March 10, 2009