Article in The Western Producer
Posted Feb. 16th, 2017 by Barb Glen
Dr. Margo Pybus heads Alberta’s surveillance team for chronic wasting disease.
And “heads” is the operative word.
As of mid-February, Pybus and her team had tested about 4,800 heads from mule deer, white-tailed deer and elk, and there are about 1,000 more to test before she issues her 2016 surveillance report at the end of March.
This year, CWD was confirmed for the first time in an elk from Canadian Forces Base Suffield, which has a herd of at least 8,000 that were moved there in the 1990s.
Although it is the first CWD case from that herd, Pybus said it isn’t a surprise.
“We know that it’s in the mule deer and some of the whitetails basically all around Suffield,” she said.
“But there isn’t a deer hunt, they don’t hunt deer on Suffield, so we were never able to get any samples from Suffield until the elk harvest started, which was in 2012, so we’ve been looking at the elk ever since.”
Ranchers surrounding the Suffield base in southeastern Alberta have long been concerned about growth of the elk herd, the damage it does to area crops and the potential for disease spread into cattle.
However, CWD affects only cervids and is not a threat to bovines.
CFB Suffield has allowed hunting and gradually increased the number of tags offered to hunters in recent years in efforts to reduce numbers.
“That’s our first elk,” said Pybus of the positive CWD result. “So that’s an indication the disease is becoming established enough that it is spilling over into other species now.
“We think it was the same thing with the one moose case. We identified that in 2012 or 2013. Again, that was interpreted as spillover from sharing range with infected deer. As it builds up more and more in the deer, there’s just more and more opportunity for it to spill over into these other cervid species.”
CWD is a brain-wasting illness thought to have initially arrived in Canada on imported U.S. deer for game farms and antler velvet operations. It is well-established in Colorado, Wyoming and Wisconsin, and was identified in Saskatchewan in 1996. Since then CWD has slowly spread in wild deer populations, where it causes the animals to gradually lose weight and die.
In Alberta, hunters are asked to provide the heads of harvested animals so they can be tested.
The province’s January interim report, when more than 3,000 heads had been tested, had identified the illness in 69 mule deer, nine whitetail and one elk.
CWD was found in animals in two regions beyond the previously known range for the disease, those being the Battle River and Vermilion River watersheds. Those two areas are adjacent to areas where CWD has been found before.
Pybus said the disease is slowly spreading westward but as for its speed, there is no basis for comparison because Alberta has the only long-term, comprehensive surveillance system for CWD.
“It’s moving. It’s a slow, insidious disease in an individual and it’s also slowly, insidiously moving up certain watersheds,” she said. “Our surveillance target each year is somewhere between 4,000 and 5,000 and we feel that validates the surveillance for giving us a fairly good resolution to putting the picture together for what CWD is doing in the province and showing where it’s going and how much it’s increasing and what rate it’s increasing at.”
Saskatchewan had a testing program from 1997 to 2012. A scaled-back program was implemented last fall and the budget allows for testing of about 300 head.
According to Pybus’s data, CWD affects mule deer in greater numbers than whitetails but the reasons aren’t established.
“We’ve had collars on mulies and whitetails and trying to tease things out. The only thing that seems to be a consistent pattern that suggests increased opportunity for transmission is that the mule deer go into their winter groups earlier than the whitetails and they stay together longer.”
Mule deer also tend to winter in larger groups than whitetails.
Statistics show male deer have higher incidence of CWD than females, which Pybus suggested might be due to the male habit of forming bachelor groups in winter that increase opportunity for disease spread.
The exact method of CWD transmission is also unknown, said Pybus. There’s strong evidence that it requires deer to deer contact, but whether that is through saliva or some other mode remains unknown.
She also said there’s evidence that an area highly contaminated with CWD fosters infection and spread but that is not the case in Alberta, where the disease is relatively new.
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