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Chronic Wasting Disease or CWD, is a progressive, degenerative disease of the brain affecting affecting deer and elk
(Cervidae) in North America.
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CWD is similar to other nervous system diseases known as transmissable spongiform encephalopathies (TSE). These include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle, and Creutzfeldt-Jakob disease (CJD) in humans.
Although the exact cause of CWD is unknown, it is associated with the presence of an abnormal protein called a prion. There is no treatment or vaccine currently available for the disease.
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There is currently no scientific evidence that CWD affects humans, but we must exercise caution since there is some evidence to suggest that BSE, or “mad cow disease”, can affect humans.
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It is not clear how CWD is transmitted, but based on experience with the disease in captive deer, both animal to animal and mother to offspring transmission may be possible; however, the most likely means of transmission is between animals
that are in close contact with each other. In addition, elk and mule deer placed in paddocks that had housed infected
cervids for many years became infected, even though there were no other
cervids on the premises, leading to the assumption that the agent could survive in the environment and transmit the disease.
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Symptoms of infected animals may include lack of coordination, separation from other animals in a herd, excess salivation, depression, unusual behaviour,
paralysis, weight loss, difficulty swallowing, increased thirst and urination, and pneumonia. Signs usually last for weeks to months before the animal dies; however some animals
may not show
clinical signs except for an
acute
pneumonia. Animals are usually 3- to 4-years of age before
clinical signs appear, but may be as young as 18 months or as old as 13 years. The disease is tentatively diagnosed based on
clinical signs, and is confirmed by isolating abnormal prion proteins during
postmortem examination of the brain stem or from samples of
lymphoid tissue from the affected animal. Current research, however, suggests that biopsies of retropharyngeal tonsils could be used to determine the presence of prion proteins in
live animals.
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CWD is an
emerging disease, that is the number and distribution of infected wild and captive
cervids has been steadily increasing since its discovery in the late 1960s at a research facility holding captive deer in Colorado.
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To date, CWD has been found in free-ranging
cervids in Colorado, Wyoming, South Dakota, Wisconsin, Nebraska, New Mexico, Illinois and in Saskatchewan and in captive
cervids in Saskatchewan, Alberta and Colorado, Nebraska, Montana, Wyoming, Kansas, South Dakota, Oklahoma and Minnesota.
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Since 1996, CWD has been diagnosed in farmed elk on 40 game ranches in Saskatchewan and two in Alberta. Measures have been taken in all cases to prevent the spread of CWD.
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In addition to several US States, Manitoba, Saskatchewan and Alberta have surveillance programs in effect to monitor CWD in free-ranging cervids.
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As of January 2003, 7 wild deer of approximately 7000 wild deer and elk sampled in Saskatchewan, have tested positive for CWD. As of January 2003, CWD has not been detected in BC.
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British Columbia initiated a CWD surveillance program of deer and elk during 2001
. The program will primarily focus on random surveys of road kills and hunter-killed deer and elk. Sick animals showing signs of CWD will also be tested. Regional offices in Cranbrook and Fort St. John are collecting road mortalities and
hunters and game cutters are assisting with harvested animal samples to provide samples.
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