Chronic wasting disease of cervids

Fact sheet

What is chronic wasting disease (CWD)?

CWD is a fatal degenerative disease of the central nervous system in cervids (members of the deer family) such as white-tailed deer and moose. It belongs to the group of transmissible spongiform encephalopathies (TSEs). CWD shares features with bovine spongiform encephalopathy (mad cow disease) in cattle and scrapie in sheep. These diseases are caused by a prion, a particle naturally present in the cells of the nervous system. The prions that cause TSEs are abnormally formed and are able to transmit that abnormality to healthy proteins. The build-up of abnormal prions destroys the nerve cells.

* Can moose also be infected with CWD?

Yes. However, because moose are solitary animals they are less likely to develop and spread the disease across a territory. Experience gained within the provinces and States affected by CWD suggests that moose contract CWD only when they share the territory with another species (for example, white-tailed deer) where the disease is well established.

* Is CWD present in Québec?

In September 2018, the first case of CWD was discovered in Québec in a cervid farm in the Laurentides region. All the animals in the farm were slaughtered. To protect the wild cervid population against this disease, the MFFP took prompt action to deploy significant operations to detect the presence of the disease in the wild population within proximity of the farm concerned and to reduce the risk of spreading the disease to wildlife. No cases of CWD have been detected in wild cervids to date. Over the next few years, enhanced monitoring will help determine whether the disease has been eliminated or whether it has spread to other cervid farm or to the wild population.

* Where does CWD occur?

The disease is spreading in North America. Since it first appeared in Colorado in 1967, it has spread across 25 other U.S. states. Closer to Québec, a few cases of CWD were detected in New York State in 2005. However, thanks to quick and effective action, no other cases have been reported since. In Canada, the disease is present in Alberta and Saskatchewan. In 2016, the first case of CWD was discovered in Europe in Norway’s deer and moose populations.

Distribution of chronic wasting disease (CWD) in North America

Distribution of chronic wasting disease (CWD) in North America  July 2019 (from the U.S. Geological Survey)
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* Why is CWD of concern?

There are no known treatments or vaccines for prion diseases.

Once CWD is introduced into wildlife, it is extremely difficult to eradicate.

CWD is fatal to infected animals. In the provinces and States where the disease is long established, there has been a significant, irreversible drop in the cervid population, resulting in impacts on hunting activities and the associated economic spin-offs.

How is the disease spread?

The precise mode of transmission of CWD is not known. Since the prion is concentrated in the urine, feces, saliva, and blood of affected animals, it is generally agreed that the main transmission routes are direct contact between members of the deer family and contamination by ingestion of prions present in an environment contaminated by infected animals. The contagious prion is highly resistant and can remain in an environment for several years.

The disease can be spread geographically by:

  • Movements of infected live animals
  • The transport of infected wild ungulate carcasses or parts thereof
  • The use of products derived from infected animals (e.g., urine)

The disease can spread from wild to farmed ungulates and vice versa. It appears to spread more rapidly in areas where high concentrations of ungulates are found, such as on farms and in feeding and baiting areas.

How can you tell if an animal has CWD?

The following clinical signs may be present in an animal with CWD, especially in the terminal stages of the disease:

  • Excessive thinness and deterioration of physical condition
  • Excessive salivation and urination
  • Subtle head tremors
  • Lowered head and ears
  • Splayed legs
  • Dull, pale, and spiky coat (the animal may keep its winter coat much longer than normal)
  • Aggressiveness, panic, or other abnormal behavior
  • Slight disturbance in coordination

Since the physical manifestations of the disease generally do not occur until 16 to 36 months after infection, an animal can carry CWD without showing any clinical symptoms.

Cerf de Virginie amaigri par la MDC.

White-tailed deer emaciated from CWD (photo courtesy of Dr. Terry Kreeger, Wyoming Fish and Game Department)
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Jeune wapiti adoptant une posture typique des derniers stades de la maladie (tête et oreilles basses, position élargie des membres).

Young elk with a posture typical of the late stages of the disease (lowered head and ears, splayed legs) (photo courtesy of Dr. Terry Kreeger, Wyoming Fish and Game Department)
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Is CWD a risk to human health?

At this time there is no scientific evidence to suggest that CWD can be transmitted to humans. However, since the disease involves prions, it is better to err on the side of caution. Health Canada recommends that any tissue that may have come from a known CWD-infected animal not be used or consumed by humans.

Is there a risk to pets and domestic animals (livestock)?

No, only members of the deer family are affected by the disease.

Is CWD a risk to wildlife?

Although CWD was detected on a farm, steps must be taken to verify if the disease is present in wildlife and limit its spread in cervid populations. CWD can be transmitted by direct contact between wild and farmed deer through fences or by indirect contact through contaminated fluids (e.g., urine, saliva, feces).

Can the disease be transmitted to others species than white-tailed deer?

CWD only affects cervids such as white-tailed deer, elk, mule deer, moose, and caribou.

How can you be sure that an animal does not have CWD?

The only way to effectively diagnose the disease is to test the brain and lymphatic tissue of an animal over 12 months of age.