Scientists watching for CWD in humans

By Anne C. Mulkern
Denver Post Staff Writer

Washington - Colorado scientists will plow through thousands of death records looking for evidence that hunters might be at risk for the same brain-wasting disease that kills deer and elk.

Chronic wasting disease plagues deer and elk in Colorado and Wyoming. Are there signs it has jumped to humans?

"So far we haven't found the evidence, but is it possible? Yes, it's possible," said Dr. Ermias Belay, medical epidemiologist at the Centers for Disease Control and Prevention, which is working with Colorado and Wyoming.

Because of the long incubation period of similar diseases, and the small pool of people in which to study the effects of eating infected meat, researchers know it could be years before they know. That is why they must stay vigilant, they said.

Researchers are concerned because chronic wasting disease is similar in form to bovine spongiform encephalopathy, which causes mad cow disease in cattle. Both diseases are caused by abnormally shaped proteins that destroy normal brain cells, eventually eating large holes in the brain.

Since mad cow can be transferred to humans, the same may be true of chronic wasting disease. Additionally, scientists know that 70 percent of all new or rapidly increasing diseases in humans come from animals, from West Nile virus to mad cow to E. coli poisoning.

"Back in the '80s and '90s the British (government) went to great lengths to say, 'Don't worry, mad cow doesn't spread to people.' They turned out to be wrong," said John Pape, an epidemiologist with the state health department who tracks diseases that can spread from animals to people.

"If mad cow could make the jump, could (chronic wasting disease)?" he said.

The CDC, in Atlanta, is attacking the question with several techniques.

Using CDC grants, Colorado and Wyoming are checking hunting licenses against a national database of deaths and their cause. Researchers will look for hunters who died of Creutzfeldt- Jakob disease, a wasting of the brain that occurs in about one in a million people.

Wyoming submitted 247,000 hunter names to the database; 2,500 had died since 1996. One died of Creutzfeldt-Jakob.

State health officials knew about that person, and the death already has been attributed to the naturally occurring type of the disease, said Scott Seys, deputy state epidemiologist for the Wyoming health department.

A higher rate of the Creutzfeldt-Jakob in hunters might indicate the need to dig further. Some people get a variant of that disease from eating cow meat infected with bovine spongiform encephalopathy.

Mad cow spread to humans after 1 million to 1.5 million cattle became infected over a 10- to 15-year period, Pape said. Even then, there were only 147 human cases, though all were fatal. That shows that Creutzfeldt-Jakob is not easily transmitted, both men said.

There are far fewer deer and elk than that, and far fewer that are infected, Pape said. And the meat usually is removed in a way that avoids nerve tissue. Mad cow is carried in tissue near the spine and in the brain.

From the start of the 2002 hunting season through Dec. 8, the Colorado Division of Wildlife tested 52,296 deer, elk and a small number of moose, and found 651 positives for chronic wasting disease.

The number of hunters bringing in game for tests is steadily dropping, which concerns the Division of Wildlife, said Todd Malmsbury, a member of the chronic wasting disease team.

"One possibility is that most people don't believe there is a connection between chronic wasting disease and human health," he said. But because that connection cannot be ruled out, and to track the disease's spread, the division wants hunters to have animals tested.

Belay said chronic wasting disease has been "endemic for decades" in northeastern Colorado, southeastern Wyoming and parts of Nebraska.

The disease was discovered in a mule deer at a Fort Collins wildlife research station in 1967. By 2002, it had spread into Wyoming, Nebraska, South Dakota, Wisconsin and to Colorado's Western Slope. It also has been found in Canada.

"We believe humans potentially had a chance to be exposed to the agent," Belay said.

In a study released in June, the CDC, Division of Wildlife and Wyoming and Ohio academic researchers looked at 12 cases since 1997 where people were believed to have died of Creutzfeldt-Jakob disease. The people had been hunters or were exposed to deer or elk meat. Researchers studied the brains of those who died.

They found no evidence linking the deaths to chronic wasting disease. The Colorado health department has compared the number of Creutzfeldt-Jakob cases in parts of the state where chronic wasting disease exists to those in areas without the malady. There was no difference between the two, Pape said.

Staff writer Anne C. Mulkern can be reached at 202-662-8907 or amulkern@denverpost.com .