Chronic Wasting Disease

New Prion Research

When Ed Hoover became interested in chronic wasting disease, little was known about the mysterious illness or what caused it. CWD is a transmissible neurological disease of deer and elk characterized by loss of body condition, odd behavior, and death.

Despite the mystery, Hoover at first was reluctant to get involved in CWD research. His work in the Department of Microbiology, Immunology, and Pathology at Colorado State focused on viruses–his research developing a vaccine against the feline leukemia virus has resulted in the near eradication of that once highly prevalent disease. But the infectious agent of CWD is neither virus nor bacteria. It appears instead to be a prion, essentially a protein without associated nucleic acids.

The discovery that proteins alone can transmit an infectious disease came as a considerable surprise to the scientific community.

One of the darkest puzzles of prion diseases is the possibility of their crossing from one species to another. Several mammalian species develop prion diseases including sheep, which develop scrapie, and cows, which develop bovine spongiform encephalopathy or mad cow disease. There is also a human form, Creutzfeldt-Jakob disease.

In England during the mid-1990s, an outbreak of mad cow disease was caused by the feeding of sheep parts to cattle. The sheep were infected with scrapie. The cattle developed mad cow by eating the infected sheep. Then people developed a form of Creutzfeldt-Jakob disease by eating the infected beef.

While the possibility of human infection from CWD is of great concern, it is important to note there have been no verified cases linking CWD to human Creutzfeldt-Jakob disease, Hoover says.

Nonetheless, after the mad cow disease outbreak, the Colorado cattle industry took notice of prion diseases like CWD. And when Hoover overcame his initial reluctance to study CWD, he found a ready ally in the Agricultural Experiment Station.

The Agricultural Experiment Station provided Hoover seed money through Colorado State's College of Veterinary Medicine and Biomedical Sciences to begin studies on the oral transmission of CWD. At the time, there was no study of the potential route of transmission of CWD, Hoover says.

"We began with a study to determine if CWD was transmitted orally. We found that it was in the tonsils and lymph nodes long before it reached the brain. We demonstrated that CWD can be transmitted through oral exposure," Hoover says.

The success of that initial study encouraged other funding agencies to invest in Hoover's work, leading to further investigations.

"We've gone on to study the nerves as the agent's transit route to the brain. We did some studies on the location of the agent in lymphoid tissue to give us some clue as to how it got there and whether the lymphoid system, which is part of the immune system, actually is participating in the evolution of the disease, because it is thought that there's no immune response in prion infections.

"We've also tried a new approach of inoculating deer with prions–an approach that is being pioneered in the study of Alzheimer's disease in humans," he says.

Earlier this year, the National Institutes of Health awarded a seven year, $8.4 million grant to a research team led by Hoover to study CWD in deer.

The goals of the project are to:

To house these studies, Hoover wants to raise additional support to build a biosecure deer housing facility in which to safely study the disease under controlled conditions.

For all the mysteries surrounding CWD, one thing is clear: The threat is real and immediate. Consider that deer and elk hunting pumped $599 million into Colorado's economy last year according to the Colorado Division of Wildlife. There's no mystery about the impact to the state if hunters quit hunting in Colorado for fear of contracting CWD.

"As far as the maximum impact of CWD, I don't think anyone knows yet," says Hoover.