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Deer disease lingers in environment, study says Chronic wasting spread from pen, carcass after 2 years

By JOHN FAUBER [email protected]

Posted: May 6, 2004

New research showing that chronic wasting disease can be transmitted through soil and from decomposed carcasses of infected deer suggests that the effort to eradicate the disease in Wisconsin may be much more difficult than once thought.

Chronic Wasting Disease

Previously, research showed that the disease could be transmitted by animal-to-animal contact.

Ever since the deadly brain disorder first appeared in Wisconsin in 2002, wildlife officials had feared that the infectious agent that causes the disease could linger in the environment.

Now there is evidence showing that the disease can persist for at least two years.

"This is an important piece, this study," said Julie Langenberg, a wildlife veterinarian with the Wisconsin Department of Natural Resources. "It verifies a concern that we have had since we started working with chronic wasting disease."

The study, which appears in the online edition of the journal Emerging Infectious Diseases, involved three types of experimental enclosures that were designed to simulate at least some of the conditions found in the wild.

One set of paddocks housed mule deer that once had been infected with chronic wasting disease, but the areas had been kept empty for about two years. Residual excrement from the sick deer remained in the enclosures.

In other types of paddocks, carcasses of infected deer had been allowed to decompose in place for nearly two years.

The researchers then brought in mule deer that were believed to be disease-free and confined them to the enclosures.

In both types of enclosures, one or more of the reintroduced healthy deer became infected within a year.

In a third type of enclosure, infected deer were kept with uninfected deer. That too resulted in the spread of the disease.

The authors of the study acknowledge that confining the deer to an area may have exaggerated the likelihood of transmission.

However, "This kind of thing could happen in the wild," said co-author Beth Williams, the researcher who in 1977 first identified chronic wasting disease as an infectious brain illness in deer.

The research reinforces the idea of prohibiting baiting and feeding in areas where the disease exists, Williams said.

In addition, she said, the research also raises concerns about efforts to eradicate chronic wasting disease.

"If all the deer are removed, there may be residual infectivity," she said. "It may be difficult to get rid of CWD."

Still, Williams said she believes the effort by the Wisconsin DNR to eradicate the disease is worthwhile.

Using hunters and sharpshooters, the DNR wants to kill as many deer in areas where animals have tested positive for the disease as possible, as well as create buffer zones around those areas.

In the eradication zones surrounding hot spots where numerous chronic wasting disease cases have been found, the DNR hopes to reduce the deer population to fewer than five animals per square mile. In the larger intensive harvest zones, the goal is 10 to 15 deer per square mile.

Judd Aiken, a professor of animal health and biomedical sciences at the University of Wisconsin-Madison, said he believes that by reducing the number of infected animals in the wild, the state stands a better chance of someday eliminating the disease.

The study is the best research to date showing how the disease can be spread in the environment, he said. What it does not show, he said, is what type of excrement carries the disease and how long the infectivity lasts in the environment.

"I don't think I would conclude that it will be permanently in the environment," he said.

Langenberg, of the DNR, said she believes the study reinforces the idea of quickly culling diseased animals from the herd.

"I still think what the state is doing makes sense," she said. "We still have a chance to control and possibly eliminate the disease. We are making the choice to act and not wait."

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Just seems the people who don't have the problem in their backyard, don't see it as a problem.

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