Chronic wasting disease: what cervid producers should know
What is chronic wasting disease
Chronic wasting disease (CWD) is a progressive, fatal nervous system disease that affects these animals, which are all part of the deer family known as cervids. It is a transmissible spongiform encephalopathy, or prion disease. It is contagious amongst cervids, like scrapie in sheep. There has been no known transmission of CWD to humans, however, bovine spongiform encephalopathy (also known as mad cow disease) in cattle has been known to cause Creutzfeldt-Jakob disease in humans.
What we know about CWD and human health
There has been no known transmission of CWD to humans. Extensive surveillance of human prion diseases in Canada and elsewhere has not provided any direct evidence that CWD has infected humans. However, experts continue to study CWD and whether it has the potential to infect other animals and humans. As a precaution, measures are in place to prevent known infected animals from entering the food chain, including:
- mandatory testing of all cervids sent for slaughter (over the age of 12 months) at all abattoirs in Saskatchewan, Alberta, Manitoba, Yukon and Quebec
- not allowing animals known to be positive for CWD to enter the commercial food chain
- reporting immediately to the CFIA all suspected cases, as CWD is a reportable disease under the Health of Animals Act
Clinical signs of CWD
Animals with CWD may show a number of different signs as the disease slowly damages their brain. They may include:
- difficulty swallowing
- excess salivation
- increased thirst
- lack of coordination
- separation from the other animals in the herd
- unusual behaviour
- excessive urination and
- weight loss
Signs can last for weeks to months before the animal dies; however, some animals may not show clinical signs. Animals are usually three to four years old before clinical signs appear, but signs have been seen in animals as young as 15 months or as old as 13 years.
Where CWD is found
In Canada, CWD has been predominantly found in wild and farmed deer and elk populations in Saskatchewan and Alberta, with 3 confirmed cases in wild moose. The disease has also been found in farmed red deer in Quebec and in a wild deer in Manitoba. 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.
How CWD is diagnosed and the limitations of testing
Although animals infected with CWD sometimes show symptoms, CWD can only be confirmed by testing specific tissues from an affected animal after it is dead. While a negative test result still does not guarantee that an individual animal is not infected with CWD, it is considerably less likely and may reduce your potential risk of exposure to CWD.
Currently, CWD tests officially approved by the Canadian Food Inspection Agency (CFIA) are designed for surveillance purposes and are not reliable enough to detect the disease in animals under 12 months of age. CFIA's surveillance testing aims to identify farmed animals over 12 months of age (who are more likely to be infected with CWD), in order to prevent contaminated meat or other consumable products from entering the market. There is currently no test available to certify that food or other consumable products are free from the CWD prion.
Treatment for CWD
No treatment is available for animals with CWD. No vaccine is available to prevent CWD infection.
Protecting Canadian livestock from CWD
The management of CWD in Canada is a joint responsibility of farmed cervid producers, provinces/territories and the federal government. CWD is a "reportable disease" under the Health of Animals Act. This means that all suspected cases must be reported immediately to the CFIA.
All cervids slaughtered in abattoirs in Saskatchewan, Alberta, Manitoba, Yukon and Quebec are required to be tested for CWD. This applies to federal, provincial and territorial abattoirs in those provinces.
Some provinces and territories offer testing services to hunters if they choose to have their carcasses tested for CWD. A negative test result does not guarantee that an individual animal is not infected with CWD, but it does make it considerably less likely and may reduce your risk of exposure to CWD. If members of the public have concerns, they should contact the provincial or territorial officials where they live or hunt.
The CFIA implemented a CWD eradication policy in October 2000. In 2002, the CFIA established national standards for CWD Herd Certification Programs, which lays out requirements for biosecurity measures to prevent CWD and mitigate the risk of infection. Risk-mitigation measures for farmed cervids also include mandatory testing and limits on which animals may be added to the herd.
The CFIA sets the national standards, provides oversight and audits the third-party administrators of the CWD HCPs. The National Standards are reviewed in consultation with industry on an annual basis.
CFIA response to outbreaks of CWD in Canada
CWD is a "reportable disease" under the Health of Animals Act. This means that all suspected cases must be reported to the CFIA for immediate investigation.
If the CFIA determines that CWD may be a cause of disease, the animal(s) will be ordered destroyed.
A confirmed positive CWD case triggers the CFIA's CWD disease response. Response actions depend on whether a herd is enrolled in a CWD HCP. Only herds that are enrolled in a CWD HCP and compliant at level D or higher are eligible for the CWD HCP disease response Herds that are not enrolled in a CWD HCP will be placed under initial movement controls and restrictions will be placed on movement of live cervids, cervid products and by-products into the marketplace. In addition, the CFIA will investigate trace-in and trace-out animals. Provinces and territories may have their own disease control requirements and measures.
Owners whose animals are ordered destroyed may be eligible for compensation.
Changes to CFIA's CWD disease response
Since the CFIA's original CWD eradication program started in 2000, the North American CWD picture has changed dramatically. Wild and farmed cases of CWD have continued to increase despite the CFIA's aggressive attempts to eradicate it. A significant re-occurrence rate has also been seen in Canadian herds that were previously depopulated, cleaned, decontaminated, and permitted to re-stock. This led to a program review and to the ultimate conclusion that eradication measures, using quarantines and stamping-out actions in areas where the disease is endemic in wild cervids, are both ineffective and unsustainable. Based on all available information, a decision was made to switch from an eradication policy to one of control.
The CFIA's new disease control program is based on the OIE (World Organisation for Animal Health) concept of compartmentalization. Compartmentalization identifies a group of animals having a distinct health status based on biosecurity management and husbandry practices. Herds enrolled on a CWD HCP and compliant at level D or higher are considered to be the compartment for CWD in Canada.
Only a few viable tools exist to deal with CWD. As a result, disease prevention is the most effective control measure. By participating in a CWD HCP, individual producers mitigate the risk through immaculate inventory control, rigorous herd testing, restricting herd entry to cervids at a similar or higher CWD HCP level, and enhanced on-farm biosecurity measures. Promoting compartmentalization in the national disease response program supports producers who are taking measures to keep CWD out of their farm.
To learn more about CFIA's CWD disease response, please consult what to expect if your animals may be infected.
To learn more about the implementation timeline of the CWD disease response program, please consult the notice to industry.
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