Scientists hunt for the causes of deer ailment

By David Steinkraus

Friday, May 28, 2004 11:46 PM CDT

RACINE COUNTY - Chronic wasting disease made an appearance in a Racine County deer this week, but Paul Madden isn't about to change his hunting habits.

"I bowhunt in Racine County," he said.

"The majority of my gun hunting is up in northern Wisconsin."

Madden, who lives in Racine, is vice chairman of the county delegation to the Wisconsin Conservation Congress and sits on the organization's executive council. He's fielded many calls from hunters wondering whether they should worry about the disease, and while he suggests people learn more, he's not worried himself.

Follow the guidelines for proper field dressing of deer, and for proper processing, and the meat is perfectly safe, he said. In fact, he added, you probably stand a greater chance of contracting Lyme disease from a tick on a deer than you do of contracting chronic wasting disease from an infected deer.

"I don't want to bring anything in my house that's going to affect myself or my family." But the danger of catching CWD, he said, is not an issue for him or his wife.

Catching chronic wasting disease has been the concern all along. CWD is part of the family of fatal brain diseases that includes scrapie in sheep, bovine spongiform encephalopathy, also known as mad cow disease, and Creutzfeldt-Jakob disease in humans, and the worry has always been that CWD can jump from animals to humans.

"Transmission to humans, certainly we have no evidence - science has no evidence - that it does occur," said Bryan Richards, CWD project leader at the National Wildlife Health Center in Madison. "But then again, science cannot disprove the possibility, same thing as with bovine spongiform encephalopathy. What one could surmise, though, is that the potential for transmission is extremely, extremely, extremely small."

Scientists still don't know precisely what causes CWD. Most say CWD is caused by a prion, a misshapen protein that twists other proteins out of their correct shapes. Last week, a paper published in the Proceedings of the National Academy of Sciences called that idea into question. A team of researchers, led by a scientist from Yale Medical School, said they purified a prion but that it didn't cause an infection in laboratory animals. They wrote that there may be a virus involved in the disease.

That's part of the minority view in the current research. Yet, Richards said, it may not be ultimately important to know precisely what causes CWD if we can lean enough about how the disease is transmitted from one animal to another and whether it crosses species.

"We now have evidence that in a rather small pen the disease can be transmitted. But does that hold true in a county or a township?" he said.

Transmission between animals is the focus of Joel Pedersen's research. He's an assistant professor of environmental toxicology and soil biochemistry at the University of Wisconsin-Madison.

Wild and domestic animals consume particles of soil while they're grooming and grazing, he said, when they go to mineral licks, or at other times. "For example bucks will lick the soil on which does have urinated to determine whether they're ready for mating." All of this hints that CWD may be transmitted in feces or body fluids, such as saliva or urine.

So Pedersen and his colleagues have several projects going to figure out whether prions can survive in the open. They're looking at how they bind to minerals and organic compounds in the soil and whether they remain infectious afterward. They're also looking at whether prions will leach through a landfill - where infected material may be placed - and whether they're affected by wastewater treatment plants because that's where water leaching through landfills is typically sent.

CWD is a relatively new disease here, and the concentration of research on it is also recent, Richards said. Although it was first described in Wyoming in the 1960s, it didn't receive much attention until an outbreak of mad-cow disease in Great Britain and its subsequent discovery in Wisconsin slightly more than two years ago.

There is the possibility that people are seeing CWD because they're looking.

"My sense, and I think this is what most people believe, is that part of the increase in the known range of chronic wasting disease is better detection," Pedersen said.

"The spread to Wisconsin and other states is probably the result of transfers of farmed deer and elk rather than some pre-existing reservoir of prions in the soil."

When you look at the pattern of CWD's spread, it looks as if the disease is new in Wisconsin, Richards said. "Already I think we're seeing indications of geographic spread, kind of in outward concentric rings, which would strongly indicate that it hasn't been here forever."

Now the hope, Richards said, is that we can learn enough about the disease, and learn it fast enough, to help the people responsible for managing the state's wildlife.

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