White-tailed bucks, does and other cervids with chronic wasting disease seem to gravitate to easy terrain. That's the bottom line of a study by Penn State College of Ag Sciences wildlife researchers.
They looked into environmental variables associated with the presence or absence of CWD in Virginia, West Virginia, Maryland and Pennsylvania. "We obtained the geographic coordinates of hunter-killed deer that tested positive for CWD and overlaid them on a map showing a variety of habitat and landscape features," explains David Walter, an assistant leader of the Pennsylvania Cooperative Fish and Wildlife Research Unit at Penn State.
"The analysis showed a high prevalence of CWD in deer sampled from low-lying open and developed landscapes," he adds. The study included only hunter-killed white-tails, not those from captive (deer farm) herds.
Those results became more important this spring when Maryland Department of Natural Resources and the state Game Commission and Department of Agriculture in Pennsylvania reported three more CWD-positive deer. Pennsylvania has found six CWD-positive deer in the last two years. Maryland and Virginia have had a few each, but West Virginia has had more than 100 during the last decade. Some – not all – were in captive herds.
Two take-homes from the study
The results suggest that state wildlife management agencies should concentrate surveillance efforts in such topography and landscapes. CWD is likely to spread in free-ranging deer, in valleys parallel to mountains and along river bottoms, most likely through developed and agricultural terrain.
It also yielded insight into how the ailment has progressed in the East, says Walter. It revealed likely paths of future dispersal of the disease, which always is fatal to cervids, such as deer, elk and moose.
Several years ago, Walter researched the spread of the disease in Colorado in free-ranging mule deer. "We weren't sure the disease would act the same way here as it did in the West, because that's a much more open landscape," he notes.
"We found out west that the lowlands, where mule deer yard up in the winter after coming down from the high elevations, had the highest prevalence of chronic wasting disease. We're seeing some of that in this region with whitetails – in low-lying areas where they come out of the forests in winter and congregate."
While it's not known exactly how CWD is transmitted, scientists believe that it may be spread both directly through animal-to-animal contact and indirectly via soil or other surfaces – most likely through the saliva and feces of infected animals or decomposing carcasses.
Wildlife scientists suspect the transport of captive deer play a major role in spreading CWD. But the spread in the East is mysterious because West Virginia and Virginia don't have a lot of game farms. Pennsylvania, on the other hand, has the second highest number in the country behind only Texas, Walter says.
And he adds that there's no known direct link to say that CWD actually spread from West Virginia to Virginia to Maryland to Pennsylvania. "We can't really connect the dots and determine a path. But we hope the pending DNA testing and genetic component of the research can help us solve that mystery."