Federal funding intensifies prion disease research

A team of researchers at Colorado State University has received a seven-year, $8.4 million grant from the National Institutes of Health to study chronic wasting disease, a fatal brain disease of North American deer and elk that scientists know little about.

Research priorities are assessing how CWD is transmitted among deer, developing a transgenic mouse model for the disease, evaluating the potential for interspecies transmission, and working on a vaccine to prevent the spread of CWD in deer and elk.

"Progress in the study of this disease has been difficult because the causative agent is a protein rather than a nucleic acid-containing agent," explained Dr. Edward Hoover, director of the university's Prion Research Laboratory in Fort Collins. "Therefore, we can't use the kind of technology we use to detect and understand viruses and bacteria."

Like bovine spongiform encephalopathy in cattle, scrapie in sheep and goats, and Creutzfeldt-Jakob disease in humans, chronic wasting disease is a transmissible spongiform encephalopathy that affects only deer and elk. It was discovered in Colorado in 1967. Today, the disease has been reported in Wyoming, Nebraska, South Dakota, Oklahoma, Montana, Minnesota, Wisconsin, and most recently in Illinois (see JAVMA, Dec. 15, 2002, page 1670).

There is no evidence that CWD has caused illness in humans. And although there is no proof that other species are susceptible to CWD, the Food and Drug Administration in November issued a directive to state public health and agriculture officials prohibiting material from CWD-positive animals to be used as an ingredient in feed for any animal species. Moreover, the FDA strongly advises against introducing free range deer and elk from CWD-endemic areas into the animal feed system.

The NIH has budgeted an estimated $24.3 million for TSE research in fiscal year 2002 and has requested $29.2 million in fiscal year 2003.

"We must determine whether CWD is a threat to our food supply and how best to stop the spread of this disease in our deer and elk herds," said Health and Human Services Secretary Tommy Thompson.

How CWD is transmitted is not known. Evidence suggests the disease is passed directly from one animal to another, but how the agent is shed from the infected animal's body isn't clear. Indirect transmission from a contaminated environment is one possibility.

Because the incubation period for CWD probably ranges between two to six years, researchers at the Prion Research Laboratory will work with the University of Kentucky to create a transgenic mouse model to better understand the pathogenesis, transmission, and intervention of the disease.

The team will also focus on detecting the CWD prion in body fluids and excretions of deer. The most challenging part of the research, however, is developing a vaccine. Since prions are thought to generate an immune response, a vaccine would seem to be unfeasible. Dr. Hoover noted that some Alzheimer's disease studies might offer hope.

"Immunization against the Alzheimer-related protein, amyloid plaques, that accumulate in the brain in some mouse models can prolong survival," he said. "CWD research may, therefore, yield findings important to human as well as animal prion infections."