Experimental Vaccine Partially Successful At Preventing CWD In Deer

By Paul A. Smith of the Journal Sentinel

In a scientific milestone that could have human health implications, an experimental vaccine was partially successful at preventing chronic wasting disease in deer, according to a recently published U.S. study.

The finding represents the first time a treatment has prevented the deadly prion infection in deer.

The work could have implications on human health and the livestock industry, according to lead researcher Thomas Wisniewski of New York University's Langone Medical Center.

"Now that we have found that preventing prion infection is possible in animals, it's likely feasible in humans as well," Wisniewski said.

Wisniewski is a physician and researcher who specializes in neurodegenerative disorders such as prion diseases and Alzheimer's disease.

The CWD vaccine study started in 2010 and was conducted at Colorado State University. Its results were published Sunday in Vaccine, a peer-reviewed medical journal.

Chronic wasting disease is a fatal brain disorder caused by a misfolded prion, or protein, in the brain. It is among a family of transmissible spongiform encephalopathies, including mad cow disease and Creutzfeldt-Jakob.

The deer disease was first detected in Colorado in the 1960s and now has been found in 22 states and two provinces in North America. It was detected in Wisconsin in 2002.

The disease has led to restrictions on transfer of farmed deer and elk and prohibitions on deer baiting and feeding in many areas.

Although it has not been shown to infect humans or livestock, the Centers for Disease Control and Prevention recommends humans not consume meat from a CWD-positive animal.

For the study, researchers exposed 11 deer to CWD. Five deer were then treated with various doses of a CWD vaccine. The other six were given placebos.

The 11 deer were housed together throughout the experiment.

Within two years, all six of the control deer developed CWD infections. The median survival of unvaccinated deer was 600 days, Wisniewski said.

The treated deer survived an average of 900 days, and one deer — which received the highest dose of vaccine — is still alive.

The vaccine was made by inserting a cervid prion gene (PrP) into weakened, or attenuated, salmonella bacteria.

The bacteria was then administered to the deer, at first through a tube and at later stages in food. The five treated deer were given various strengths of the vaccine over 11 months.

The treatment produced the prion protein inside the animals' guts and triggered their immune systems to produce "anti-prion" antibodies, according to researchers.

The work represents a breakthrough in prion disease treatment.

"It is the very first time a vaccine approach has been shown to have efficacy in a species naturally at risk for prion infection," Wisniewski said. "That's very encouraging for future work and developments."

Although wildlife officials in the United States and Canada have tried to prevent the spread of CWD in wild and captive herds, the disease has continued to show up in new areas and increase in prevalence.

No treatment exists for CWD and the other prion diseases. The allure of a cure for CWD has attracted attention from governmental agencies, private companies and universities.

Earlier this month the Canadian government announced a $1.16 million investment in a CWD vaccine study being conducted at Pan-Provincial Vaccine Enterprise (PREVENT) in Saskatchewan.

If proven successful through further testing, a vaccine would have the greatest application to captive cervids. It's much more difficult, but not impossible, to administer vaccines to wild animals. A rabies vaccine, for example, is added to food and dropped from aircraft to treat raccoons and foxes.

Dave Clausen, a retired veterinarian from Amery and former head of the Wisconsin Natural Resources Board, urged caution about the results.

"It's a step in the right direction," Clausen said. "However, it's a long way from becoming a reality, especially in wild deer."

Clausen said among the questions that remain unanswered were how long any immunity would last and whether it can be passed from adults to offspring.

Then there is the danger of false hopes.

"Hunters might say, 'Why worry about CWD, it's almost cured,'" Clausen said. "The costs of dealing with CWD will always be lower if the disease is contained to the smallest possible area and to the fewest number of deer."

The CWD vaccine study was funded through the National Institutes of Health and the Seix Dow Foundation.

For his part, Wisniewski termed the work "partially successful."

"We have a ways to go, certainly," Wisniewski said. "We're hopeful we will be able to follow this work with another study, and that others will pursue the similar treatments. It represents a new era in the study and potential treatments of prion diseases."