Many unknowns surround disease


To this date there is no proof of a human dying from or being infected with chronic wasting disease.

But scientists don't want to rule out the possibility because there is not enough scientific proof saying the disease recently discovered in two wild mule deer at the Motherwell Ranch south of Hayden cannot affect humans, said John Pape, an epidemiologist with the Colorado Department of Public Health and Environment.

Pape said Thursday scientists still don't know that much about chronic wasting disease.

"There has been no evidence to date that the disease has happened in people," Pape said. "The concern is while evidence suggests it doesn't transmit to people, there is not enough evidence to say it is impossible."

Chronic wasting disease belongs to a family of diseases known as transmissible spongiform encephalopathies.

Other diseases in the family include scrapie, which has been known to infect sheep for more than 200 years, and bovine spongiform encephalopathy, often called "mad cow disease."

Scrapie has been known about for two centuries and has never infected humans, Pape said.

When "mad cow disease" broke in Europe about 10 years ago, people were not concerned because they thought it was similar to scrapie, Pape said. Since then approximately 100 people have died from consuming cattle infected with the disease.

"When mad cow disease broke they thought it looked similar to scrapie so they assumed it did not affect humans," he said. "They soon found out it does."

Scientists have not found a link between chronic wasting disease and diseases in humans, but it doesn't mean they won't continue to look.

"The bottom line is this whole group of diseases falls under the same category," Pape said.

Pape said scientists are not yet sure how the disease is transmitted from one animal to another.

"Exactly how it is transmitted is unknown," he said. "But evidence supports that the animal is infected by digestion of the prions."

Prions are abnormally shaped proteins that attack the animal's brain causing chronic wasting disease.

Since 1996, in an effort to eradicate the disease, officials and hunters in Northeastern Colorado have killed more than 10,000 deer.

Infection rates of one to 15 percent have been discovered in the area.

Last week's discovery at the Motherwell Ranch was the first time the disease has been detected on the Western Slope.

Live animals cannot be tested for the disease, which is why so many have been killed in the endemic area and why 300 wild deer have been killed in the area of the Motherwell Ranch, officials have said. Killing deer and elk in infectious areas is not only done for testing purposes, but as a way to control the spread of the disease.

Pape explained why killing deer and elk helps prevent the spread of the disease.

"We know with communicable diseases the more you put together the better the disease transmits," he said.

For example, if people infected with the flu are confined to an area of several miles with 40 other people, those infected with the disease are not likely to infect the other people.

But if that same group of people is confined to an airplane, the rate of infection will be significantly higher.

"The idea of killing deer on the Eastern Slope is to reduce the number of deer packed together in a small area,"

he said.

Although the infection rate for elk is far less than the infection rate for deer (less than 1 percent of elk have been found to be infected), Pape said "the problem with ranching is a lot of animals are confined to a small space," he said.

The outbreaks in Northeastern Colorado have forced scientists to take a hard look at the issue in recent years, Pape said.

"Science on this issue has been proceeding ahead at a good clip in the last five to ten years," he said. "A lot of world scientists are really beginning to look at this."

One setback in testing has been the length of time it takes the disease to appear in an animal once it has been exposed to the disease.

"The incubation period is a problem," he said.

"The time from exposure to when the disease appears can be anywhere from a year to a decade."

But scientists will continue to learn more, Pape said.

"Twenty years ago the idea of having a protein that can cause a disease was crazy," he said. "In 1997 a guy won a Nobel Prize for his study in the field. We're trying to learn as much as we can about it while trying to control it at the same time."

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