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Hunter Surveillance: Chronic Wasting Disease in Alberta's Cervids
Chronic Wasting Disease is a growing concern among Alberta’s cervid populations. Understanding the disease, from its origins and pathology, to its risk to human and animal populations, as well as current surveillance efforts to track and monitor the spread of the disease, is vitally important, particularly during hunting season, as hunters across Alberta observe and harvest deer, moose, elk, and caribou.
What is Chronic Wasting Disease?
Chronic Wasting Disease (CWD) is a naturally occuring and fatal disease that attacks the nervous system (brain, spinal cord, and other tissue) of commercially farmed and wild cervids.
CWD is a prion disease and is grouped under the family of diseases called transmissible spongiform encephalopathies (TSEs). It shares features with other TSEs, such as bovine spongiform encephalopathy (BSE) in cattle; Scrapie, which affects goats and sheep; and Creutzfeldt-Jakob Disease in humans; but it’s important to note that CWD is distinct from other TSEs and, at this time, it is known only to affect members of the cervid family; however, the potential for CWD to be transferred to humans cannot be excluded.
According to the Alberta Prion Research Institute, “Prion diseases are caused by the misfolding of normal cellular prion protein into an abnormal infectious form. These diseases are transmissible from host to host of a single species and sometimes from one species to another.”
All prion diseases are fatal. It is not known why or how prions and other proteins misfold or what mechanism causes the nerve cells in which they collect to die. Thus far, there are no vaccinations, treatments or cures for these diseases.
Origins of CWD
CWD was first observed in the 1960s, in a Colorado mule deer population held captive for research purposes. Although it was described as a syndrome, it was not officially identified as a TSE until the 1970s. What is not known (and may never be known) is if CWD arose spontaneously in wild cervid populations or if it’s linked to scrapie-infected sheep, since sheep grazed prominently along Colorado’s east slope share of the Rocky Mountains in the early 1900s and would have come into contact with local mule deer population. It might also be possible the CWD arose in captive cervids and had biological features making transmission to wild cervid populations possible.
How is CWD transmitted?
The way in which CWD is transmitted is not fully known. Prevailing theories suggest it passes through feces, urine and saliva, and can potentially be transmitted from one animal to another, from mother to fetus, or indirectly due to CWD’s presence in the environment—contaminated pastureland appears to be a factor in some CWD epidemics in commercially raised cervid populations. More research is required to understand the minimum and maximum incubation periods for CWD, although it is believed the minimum incubation period is ~16 months. It is also uncertain at what point of infection cervids begin shedding the CWD agent.
What are the clinical signs of CWD and how is it diagnosed?
Once CWD is contracted, signs of of the disease may not be observable for many years. When symptoms do become apparent, they consist of drooping ears, heavy salivation, severe weight loss, difficulty swallowing, trouble judging distance, and behavioural changes. All of these correlate with the advance of the disease, as it increasingly affects an animal’s nervous system and brain tissue.
A key challenge facing CWD surveillance efforts is that these signs can occur as a result of other diseases and are not specific to CWD. Accurate diagnosis of CWD can only be achieved through post mortem testing of an animal’s brain and lymphoid tissue.
Is there a risk to humans?
There is no scientific evidence to suggest that CWD can affect humans. However, the World Health Organization and Health Canada both recommend against consuming any meat potentially infected with CWD.
Is there a risk to livestock?
Fortunately, cattle and other domestic livestock appear to be resistant to infection of CWD, and, to date, there are no reported cases of infected cervids transmitting the disease to domestic livestock.
Range of the disease
Currently, positive tests for CWD have only been confirmed in isolated areas of Saskatchewan and Alberta. Here’s a map of CWD’s range across North America.
Hunter surveillance program
CWD surveillance has been ongoing in Alberta since 1998 and the province currently has one of the best available data sets for tracking the disease. Hunters play a critical role in the success of this program and in ensuring healthy wildlife populations for future generations. The latest update on the CWD surveillance program.
For a list of affected WMUs, please refer to link above, and the 2021 Alberta hunting regulations (Page 64). For more general chronic wasting disease information check the Alberta website for details.Related Links: Chronic Wasting Disease (CWD) - Fact Sheet from the Canadian Food Inspection Agency