Chronic wasting disease of cervids

Fact sheet

What is chronic wasting disease?

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.

Where is CWD found and is it present in Québec?

CWD is spreading in North America. Since being identified in Colorado in 1967, it has spread to 24 other U.S. states and two Canadian provinces, Alberta and Saskatchewan. Closer to Québec, a few cases of CWD were detected in New York State in 2005, but no other cases have been detected since, thanks to a rapid and effective response. CWD was detected for the first time in Europe in 2016, in reindeer and moose in Norway.

Distribution of chronic wasting disease (CWD) in North America

Distribution of chronic wasting disease (CWD) in North America  September 2018 (from the U.S. Geological Survey)
Click on the image to enlarge it

In Québec, an isolated case of CWD was confirmed in September 2018 on a deer farm in the Laurentides administrative region. The Canadian Food Inspection Agency, Ministère de l’Agriculture, des Pêcheries et de l’Alimentation (MAPAQ), and MFFP are investigating to determine the origin of the contamination.

No other cases have been detected at this time in Québec under the monitoring programs conducted by MAPAQ on cervids in captivity and by MFFP on cervids in the wild.

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. A decline in the cervid population would affect hunting and its associated economic benefits.

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)
Click on the image to enlarge it

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)
Click on the image to enlarge it

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 other cervid species?

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.

Québec deer under observation

Early detection of CWD in Québec is critical to increase the chances of eliminating the disease and limiting its spread, while reducing the costs associated with these activities. That is why the Ministry has implemented measures to protect wildlife from CWD. Since 2007, the Ministry, in collaboration with Ministère de l’Agriculture, des Pêcheries et de l’Alimentation, has been carrying out a monitoring program for wild deer in areas most at risk for the introduction of CWD, namely in southernmost Québec. More than 9,500 deer have been tested over the past 10 years, and no cases of CWD have been detected.

Nombre de cerfs de Virginie analysés pour la maladie débilitante chronique (MDC) dans le sud du Québec d'octobre 2007 à décembre 2016.

Number of white-tailed deer tested for chronic wasting disease (CWD) in southern Québec from October 2007 to December 2016.
Click on the image to enlarge it

Originally the program centered on collecting and testing white-tailed deer killed in vehicle collisions, but since 2013, the vast majority of animals tested for CWD have been harvested deer, particularly in the Estrie and Montérégie regions. The risk of introducing the disease is considered lower in the rest of the province, so monitoring is less intensive. The specimens tested there have mainly been members of the deer family showing clinical signs associated with CWD. Although few in number, these specimens are a priority for sampling since they are more likely to be infected with CWD.


Quick links