Chronic wasting disease on the Canadian prairies.
Chronic wasting disease in cervids continues to spread slowly across North America including the Canadian Prairie Provinces. The disease is now present in wild cervids in at least 15 US states and has continued to spread within the provinces of Saskatchewan and Alberta. Attempts at managing the disease have for the most part been abandoned and even interest in surveillance to track its progress and effects has waned. For example, the number of heads of hunter shot deer, elk and moose submitted for CWD testing in Saskatchewan has declined from a peak of almost 7000 in 2004 to approximately 1000 in 2011. This is in spite of no cost to hunters for submitting heads for testing and in spite of programs to encourage hunters to submit heads from specific wildlife management zones where enhanced surveillance is critical to understand the disease’s current distribution. Similar declines in hunter participation in CWD surveillance programs have been reported in other jurisdictions.
This apparent apathy comes at a time when evidence is accumulating that CWD will cause population declines and altered age structures. In the only population of free-ranging deer in Canada being closely monitored for changes in CWD prevalence and survival, we estimate CWD prevalence in adult deer is now approximately 50% and is the main cause of mortality in adult deer. The study area is immediately adjacent to one of the first elk farms to test positive for CWD and it is likely that close to 15 years of infection in this wild population has resulted in ever increasing environmental burdens of prions which is now driving the outbreak. Detailed radio-tracking and motion sensitive photography is showing that mule deer in this area repeatedly and heavily use anthropogenic sites such as leaking grain bins, cattle salt blocks, hay bales, etc. Increased congregation and contamination of these sites with urine, saliva and feces increases the risk of CWD transmission. In essence these wild deer are behaving similar to deer on game farms except their movement isn’t constrained by a fence. The outcome is likely to be the same, extremely high infection rates and drastic population declines.
Because of its long incubation period and long environmental persistence, it will take decades before the effects of chronic wasting disease in wild cervids will be known. One thing is for certain, chronic wasting disease is now an integral part of the ecology of deer. Hunters and wildlife management agencies have yet to come to grips with this new reality. Strategies to manage deer and set hunting regulations will need to be evaluated based on their effect on CWD. Long term research programs and sustained commitment by hunters and wildlife agencies are needed in order to develop a rational strategy for dealing with this disease.