TWS Member Creates Risk Framework for CWD in Montana

By Joshua Rapp Learn

A mule deer buck at a ranch in Montana. While chronic wasting disease has yet to make inroads in the state, a new study examines the most likely places it will enter in an effort to guide future management resources.

Image credit: Scott Ackerman,

Wildlife managers in Montana now have a better focus on where a deadly prion disease that kills deer may infiltrate the state.

“The overall goal was to help Montana focus their surveillance,” Robin Russell, member of The Wildlife Society, said about a new study in the Journal of Wildlife Management. Russell is a research statistician at the U.S. Geological Service’s National Wildlife Health Center and the lead author of the recent study.

Although chronic wasting disease (CWD) hasn’t yet been confirmed in Montana, it can be found in some neighboring states and Canadian provinces to the north. But the researchers wanted to know where the prion disease was most likely to appear in the state, if and when it does.

Deer density makes it easier for the disease to spread, so researchers did surveys to determine where the most concentrated populations in Montana were located based on ecosystem type. They extrapolated this information to make larger estimates about deer populations across the state in different ecosystems.

They then looked at confirmed cases of CWD in neighboring states and provinces to find where the largest danger of infiltration would come.

The areas that presented the greatest danger for the state were in the north central, close to infected deer in Alberta, and in southeast Montana near Wyoming. Aside from being close to confirmed cases of CWD in these neighboring areas, these two zones also had large deer densities.

Russell said that while it would be nearly impossible to stop infected deer from crossing over to Montana, identifying areas of greatest risk could allow state managers to better control the spread of CWD.

“In Montana their main surveillance is looking at carcasses of harvested deer,” she said. “Early detection of the disease is the best way to control [CWD].”

Montana currently has bans on the import of venison from areas with CWD, and the state banned new captive cervid facilities around the turn of the century in an effort to better control it. But funds for CWD testing have declined since the study began, and Russell said this could make the control of the disease more difficult.

“It’s possible that it’s in Montana already, and they just haven’t found it yet,” she said.

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society.

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