Chronic wasting disease transmitted via environment

ARLINGTON, Virginia, May 13, 2004 (ENS): Transmission of chronic wasting disease can take place not just through animal-to-animal direct contact but also by exposure to environments contaminated by whole carcasses or excrement of infected animals, a team of researchers from Colorado and Wyoming reports.

Colorado Division of Wildlife veterinarians Michael Miller and Lisa Wolfe, Colorado State University scientist Thomas Hobbs and University of Wyoming scientist Elizabeth Williams made the discovery, and they expect it to change the way wildlife managers handle their responses to the disease, which is similar to mad cow disease.

Miller said, "We have long suspected that chronic wasting disease could be transmitted when healthy deer were exposed to excreta and carcasses of mule deer that had the disease," said Miller. "Our findings show that environmental sources of infection may contribute to chronic wasting disease epidemics, and illustrate how potentially complex these epidemics may be in natural populations."

The research confined healthy deer in three sets of separate paddocks. In the first set, healthy deer were exposed to another deer already infected with chronic wasting disease; in the second set, deer were exposed to carcasses of deer that had died of chronic wasting disease; in the third set, deer were confined in paddocks where infected deer had previously been kept.

A few of the healthy deer contracted chronic wasting disease under all three exposure scenarios over the course of one year.

"We've had a great deal of circumstantial evidence suggesting that indirect transmission occurs," said Williams. "The experimental findings show that we need to consider several potential exposure routes when attempting to control this disease."

"Ultimately, we want to develop models that predict the behavior of the disease," Hobbs explained. "For example, we would like to predict how prevalence changes over time in different areas of Colorado."

Hobbs said previous disease models have been based on animal-to-animal contact as the sole source of infection and that disease prevalence was expected to decline as the number of infected animals is reduced. But the new finding that contaminated environments can transmit the disease means that declines in infection rates may be much slower than would be predicted by models that only consider animal-to-animal transmission."

Most researchers believe the disease is caused by an aberrant prion protein that misfolds in the brain, destroying brain tissues as it progresses in the same process that causes mad cow disease and its human form variant Creutzfeldt-Jakob Disease.

Symptoms include lethargy, excessive salivation, loss of wariness of predators and slowly deteriorating body condition. The disease is always fatal and there is no known cure or treatment to prevent chronic wasting disease.

Federal and state health officials have found no connection between chronic wasting disease and human health. As a precaution, officials recommend that the meat of animals infected with chronic wasting disease should not be eaten.

Chronic wasting disease is a fatal neurological ailment of elk, white-tailed deer and mule deer.

Miller said that while the research shows environmental contamination is possible in a captive setting, the impacts in the wild are still unknown.

"Diseases like chronic wasting disease are poorly understood and of rising concern," said Sam Scheiner, program director in NSF's division of environmental biology, which funded the research. "This study provides significant new information showing the potential for transfer of the infection through the environment after many months.

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