Description
Chronic wasting disease (CWD) belongs to a group of related diseases called Transmissible Spongiform Encephalopathies (TSEs), which include:
- Scrapie in sheep and goats
- Bovine Spongiform Encephalopathy (BSE) in cattle
- Creutzfeldt-Jakob Disease (CJD) in humans
While CWD and BSE are both TSEs, it is important to note that they are not the same disease and have differences in mode of transmission and clinical signs. Also, CWD is not known to affect humans.
TSEs are associated with the accumulation of abnormal proteins (prions) in the brain. Currently, no treatments or vaccines are available for these diseases.
Clinical signs
Farmed cervids with CWD may not exhibit observable signs of disease for a number of years. Eventually, as more brain tissue is affected, animals may exhibit:
- loss of condition
- excessive salivation
- trouble swallowing
- difficulty in judging distance
- changes in behaviour
- drooping ears
Unfortunately, these signs are not specific to CWD and can occur with other diseases as well.
Currently the only way to diagnose CWD is by examining the brain or lymph tissues after the animal has died.
How to report
CWD is a federally reportable disease under the Health of Animals Act. It is also a provincially reportable disease under Alberta's Animal Health Act.
All suspected or confirmed cases must be reported by contacting the:
- district veterinarian at your nearest CFIA office
- Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:
Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
Fax: 780-415-0810
Where it’s found
Canada
In Canada, CWD has been predominantly found in wild and farmed deer and elk populations in Saskatchewan and Alberta. There have been sporadic confirmed cases in wild moose. The disease has also been found in farmed red deer in Quebec. It has not been detected in wild cervids in other provinces or territories in Canada, and has not been detected in wild caribou anywhere in North America. For more information on reported cases in Canada, see CWD: What cervid producers should know (CFIA).
For detailed annual Alberta CWD test results by species, see Mandatory Chronic Wasting Disease Surveillance Program.
North America
CWD has been detected in free-ranging cervids in 24 states and 2 provinces, and in captive cervid facilities in 17 states and 3 provinces. Visit USGS National Wildlife Health Centre for a current map of CWD cases in North America.
International
CWD has also been reported in Northern European countries including Finland and Norway. For more information, see the Finnish Food Authority and Government of Norway websites.
How it spreads
The exact mechanism of transmission is unclear at this time. However, it is known that the disease can spread from one animal to another, and females can pass it to their offspring. Surveillance information from wildlife indicates that CWD is more prevalent in males than in females.
Experimental and circumstantial evidence suggests infected deer and elk probably transmit the disease through contamination of water, soil and feed by saliva, urine or feces. CWD seems more likely to occur where elk or deer are crowded or where they congregate at feed and water stations. A heavily contaminated environment can be a source of infection.
Scientific evidence suggests that it is unlikely that CWD can be passed to domestic cattle or bison under natural conditions. To date, research in the United States indicates cattle are not susceptible to oral exposure to CWD.
CWD has been experimentally transmitted by artificial means to mice, ferrets, mink, goats, squirrel monkeys, macaque monkeys, cats and calves.
Risk to humans
There is no scientific evidence to suggest that CWD can affect humans.
- No human cases of CWD have been detected through surveillance of human prion diseases.
- Under experimental conditions squirrel monkeys and transgenic mice (laboratory mice carrying human genes) have been infected with CWD.
- In 2017, preliminary results from a Canadian and German research team showed that CWD was transmitted to macaque monkeys that were fed infected meat or brain tissue from CWD infected deer and elk.
- As a precaution, the World Health Organization recommends removing any CWD-infected animal from the human food system.
Under Alberta’s Mandatory Chronic Wasting Disease Surveillance Program elk and deer farmers are required to submit the heads for CWD testing from all farmed animals over one year of age that die or are slaughtered. Products from slaughtered animals must be held at abattoirs pending CWD negative test results. Meat from any CWD positive animal must be removed from the food chain.
Prevention and control
Provincial
In July 2004, the Alberta Government ended a moratorium on importing elk and deer by approving a cervid import protocol that allows elk, white-tailed deer and mule deer to be imported into the province from Saskatchewan for immediate slaughter at federally inspected abattoirs.
In September 2004, the Alberta government adopted stringent import protocols allowing elk, white-tailed deer and mule deer from anywhere in Canada and the United States to live on Alberta farms. To qualify for importation into Alberta, cervids must meet strict criteria to ensure that CWD is not imported into the province. Both of these policies were developed based on a scientific risk assessment.
For detailed annual Alberta CWD test results by species, see Mandatory Chronic Wasting Disease Surveillance Program.
The Alberta government, in conjunction with hunters and landowners, monitors the occurrence and spread of CWD in non-farmed (wild) cervids. Find information about surveillance and disease control programs for, and the current status of, CWD in wild cervids in Alberta.
Federal
In Canada in general, efforts to eradicate CWD in the farmed cervid population have not been successful. The CFIA's current approach aims to reduce the risk of the disease spreading by encouraging producers to adopt strong risk mitigation measures.
Enrolling in a Voluntary Herd Certification Program (VHCP) is important to help prevent the introduction of CWD to a farm. A VHCP requires enrolled producers to take measures to mitigate the risk of CWD, including ongoing surveillance testing of mature dead cervids and implementation of biosecurity measures.
Since April 1, 2019, the CFIA will only order depopulation with compensation for affected herds that have achieved level D or higher of a VHCP. Generally, these herds will have participated in a VHCP for 12 months or more.
If CWD is detected in a cervid herd not enrolled in the VHCP, the Office of the Chief Provincial Veterinarian will work with the affected producer to mitigate the risks of CWD spread.
Resources
Chronic wasting disease in wild cervids
Chronic wasting disease of deer and elk (CFIA)
USGS National Wildlife Health Centre