A single case draws caution
A Missouri deer was diagnosed with Chronic Wasting Disease, a fatal neurological disease of cervid animals (deer, elk and moose).
The whitetail deer was found early 2010, after being inspected as part of the state’s CWD surveillance and testing program. The animal was born and raised on the deer-elk game farm in Linn County where it was detected. The CWD diagnosis was confirmed by USDA’s National Veterinary Services lab at Ames, Iowa. It’s the first animal—wild or captive—to be confirmed with CWD in Missouri.
For Dr. Taylor Woods, Missouri State Veterinarian, it’s one too many. “CWD hasn’t been around [or known about] for that long. It’s a new kind of disorder; one with no vaccine to prevent it and no effective treatment to cure it. However, there’s no evidence that CWD poses any threat to domestic animals or humans.”
As Dr. Woods said, CWD is a relatively new malady. The first known case in the U. S. was in 1967, in a captive mule deer at the Colorado Division of Wildlife research facility at Fort Collins. In the 40-plus years since, CWD has been detected in both captive and wild deer and elk in 16 other states (and two Canadian provinces) including Missouri neighbors Illinois, Kansas, Nebraska and Oklahoma.
Complicating the veterinary effort, CWD has a different pathology from most animal diseases. Whereas most contagious diseases are caused by bacteria or viruses, CWD is thought to be caused by a “prion,” a renegade protein without associated nucleic acids. It produces lesions in the brains of infected animals and is characterized by loss of body condition, behavioral abnormalities, and eventually death. Along with other prion-caused diseases, CWD is classified as a “transmissible spongiform encephalopathy” and is similar in many respects to scrapie in sheep, so-called “mad cow” disease in cattle and Creutzfeldt-Jakob syndrome in humans. CWD is transmitted by live animal-to-animal contact, and, possibly, soil-to-animal contact. All spongiform encephalopathy diseases are host-specific, infecting only individuals within a particular class of animals.
Although Missouri had witnessed no CWD outbreak before the isolated incident last winter, government officials had installed several “just-in-case” measures over the past few years. Among them, adding CWD to the mandatory reportable diseases list, banning imports into the state of live deer or elk from any region with CWD infections (except animals from certified CWD-free herds), and the establishment of a multi-agency task force to draw up a contingency plan if and when CWD hit Missouri.
“Once we had a confirmed case [of CWD], Missouri departments of Agriculture, Conservation, Health and Senior Services, along with USDA, activated the contingency plan and it worked well,” said Dr. Woods. “We were able to follow well-rehearsed steps to meet the CWD challenge.
“We began by putting a quarantine on the 800-acre tract in Linn County, where the CWD-positive deer was found,” he went on. “And we sampled the remaining 50 deer on that farm, with no further signs of CWD.”
In addition, the Missouri Department of Conservation has sampled 153 free-ranging wild deer within a 5-mile radius of the game farm, plus samples taken from hunter harvested deer during the season, all with no CWD-positive results.
“We will continue to monitor native deer in the area for some time,” said Lonnie Hanson, MDC deer biologist. “CWD doesn’t just spontaneously generate—it must be transmitted from another infected animal and if there’s another CWD-positive deer out there, we intend to find it.”
“With the help of hunters and landowners, MDC has tested more than 24,000 free-ranging deer for CWD from all parts of the state since 2002 with no positive deer found,” said Bob Ziehmer, MDC director. “This is good news and we appreciate the cooperation and support from more than 120 area landowners and sportsmen in harvesting deer to obtain the samples we studied in the Linn County case.”
To analyze animals for CWD, scientists must examine brains or lymph nodes, which understandably is done post mortem. Ziehmer noted that those deer killed did not go to waste: about 5,000 pounds of processed venison were donated to the Share the Harvest program.
“Some hunters may be concerned about CWD in wild deer, although we haven’t found any infected native deer,” Hanson said. “I’m an avid deer hunter myself and I often hunt within a few miles of where the CWD-infected deer was found. I plan to deer hunt next fall.
“Of course, no one is happy we’ve had a CWD case in the state—and we hope we don’t have another one—but we’re in better shape now than we would have been 10 years ago,” he continued. “We still don’t understand the disease thoroughly, but it has been around long enough that we can deal with it pretty much as another deer disease, knowing there’s no link to other classes of animals or humans.”