Field Notes: Deer Disease at Our Door

Chronic wasting disease, a fatal, degenerative illness of deer and elk, was recently detected in South Dakota and Wisconsin. To try to prevent its spread through Minnesota’s wild deer herd, state wildlife officials will test more animals for the disease this fall. They will also consider additional restrictions on captive deer and elk herds in the state.

This spring the DNR adopted a management program for combating the disease. Among its recommendations:

• Step up testing of the brainstems of hunter-shot deer in areas where the disease is most likely to appear.
• If the disease is discovered, test more deer in the area.
• Shore up weaknesses in the regulation of captive herds that might spread the disease to wild deer and elk. (For example, said DNR deer research biologist Glenn DelGuidice, there are no fence regulations to prevent wild and captive animals from mixing or touching noses. Nor is it illegal to free captive white-tailed deer from game farms. Nor does the state always mandate testing for the disease.)
• Provide information for hunters, meat processors, elk and deer farmers, and the general public.

"All of that obviously is going to cost some money," said DNR wildlife resource manager Ed Boggess.

Chronic wasting disease is costing several states money these days. It affects elk and white-tailed, black-tailed, and mule deer. Resembling bovine spongiform encephalopathy, so-called mad cow disease, it causes loss of weight and strength, excessive salivation, and increased drinking and urination.

Unlike mad cow disease, there is no evidence chronic wasting disease can infect humans. Nonetheless, agencies including the World Health Organization have advised people not to eat any meat or other tissue from deer or elk that appear sick.

Much of chronic wasting disease remains a mystery. Scientists don’t know what causes it, though they suspect abnormal self-replicating proteins called prions. Nor do scientists know how the disease is transmitted, though it clearly can spread from animal to animal, probably through feces, saliva, urine, or contaminated food and water.

First identified in a mule deer held in a northern Colorado wildlife research facility in 1967, chronic wasting disease spread to wild deer and elk in northeastern Colorado and southeastern Wyoming by the mid-1980s. In May 2001 it was discovered in wild deer in southwestern Nebraska. It also appeared in captive herds in the United States and Canada.

Last fall, a white-tailed deer shot in southwestern South Dakota tested positive; so did three whitetails shot just west of Madison, Wis.

How did the disease apparently leapfrog past Minnesota?

DelGuidice suspects it was most likely spread as game farms shipped elk or deer across state lines. "South Dakota was a hot spot for chronic wasting disease in captive elk facilities," he said. "My best guess is that this was introduced through captive animals." The disease could spread from captive animals to wild, DelGuidice said. Further testing and investigation in Wisconsin might answer the question of how it got there.

It is possible the disease may have spread naturally through Minnesota eastward to Wisconsin, DelGuidice said. Even where the disease is prevalent, the infection rate is usually less than 5 percent. Minnesota has tested about 55 wild deer; additional testing will be required to determine if chronic wasting disease is in Minnesota.

The disease could arrive in Minnesota by either of those means. Perhaps it already has. "I can’t say that’s impossible," DelGuidice said. "The more we test, the more confident we’ll feel we don’t have it. Or we’ll know we have it."

For more information on chronic wasting disease, visit the most recent Minnesota DNR fact sheet.