One-third of Boulder’s deer infected with chronic wasting disease

A new study shows one out of three mule deer in south Boulder suffers from chronic wasting disease – and those results mean the traditional approach of killing infected animals to fight the disease probably won’t work, researchers say.

Chronic Wasting Disease Study Results (PDF)

“Everything that’s been tried to control chronic wasting disease really fails in the face of that kind of infection rate,” said Heather Swanson, a wildlife ecologist for Boulder’s Open Space and Mountain Parks Department.

In a memo to city leaders, Boulder’s open space officials said they no longer favor killing to deal with chronic wasting disease. The Boulder City Council, which can also set land-management policies for the city’s open space properties, hasn’t yet weighed in on the matter.

Researchers from the Colorado Division of Wildlife and the city teamed up starting in 2005 to study the mule deer population – the first study of its kind to take place in Boulder, Swanson said. The study focused on deer in an area bordered by Baseline Road on the north, Eldorado Springs Drive on the south, Broadway on the east and the Flatirons on the west.

During the study, ecologists tranquilized 115 mule deer, affixed them with radio collars and tested them for chronic wasting disease, an affliction similar to “mad cow disease,” in which misfolded proteins riddle an animal’s brain with holes, eventually killing it.

They found that overall, 29 percent of the deer tested had the disease. Those animals on average died much sooner than non-infected deer, and they often fell prey to mountain lions. Swanson said many of the infected deer preyed upon by cougars didn’t show symptoms that were obvious to human researchers.

“The mountain lions seem to be much better at detecting it,” she said.

Forty-one percent of male mule deer were infected, compared with 20 percent of females, because males cover more territory, which puts them at higher risk of being exposed to the disease, Swanson said.

Scientists still don’t know exactly how chronic wasting disease is transmitted, although researchers suspect it’s passed on from the urine, feces or saliva of infected animals. Swanson said some research suggests that the prions may stick to clay soils as well.

For the past several years, land managers have consistently said the best way to curb the spread of chronic wasting disease is to find infected animals and kill them. But killing one-third of any deer population isn’t a realistic approach, Swanson said, and could do more harm than good.

Diseased animals can still reproduce, thereby contributing to the health of the population, she said – something they wouldn’t be able to do if they were killed as soon as they were shown to be infected.

“With a population that’s in a precipitous decline, removing that large of a number of animals probably isn’t a good idea,” she said. “They may still be contributing to the population” before dying of the disease.

In the memo to the Boulder City Council, open space scientists said the disease has resulted in fewer deer in and around Boulder.

“The occurrence of chronic wasting disease in this population over the last two decades … has coincided with a measurable decline in estimated deer abundance in this area since the late 1980s,” according to the memo.

Swanson said scientists are hoping ever-increasing numbers of deer don’t get infected, and she said some models of the disease predict the infection rate should level off soon. That’s because chronic wasting disease is thought to require a certain level of deer density to spread quickly – once sufficient numbers of deer die, that density is depleted and the rate of infection slows.

That’s the hope, anyway. Swanson said there’s really only one way to know for sure.

“At this point, we’re just recommending that we watch the population and see what happens,” she said.

By Ryan Morgan
Dienstag, Dezember 16, 2008

Source: Colorado Daily

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