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Long-term research shows cattle resist oral exposure to CWD

Cattle from endemic CWD areas slaughtered for human consumption are likely to pose no risk to people.

Tim Lundeen 1

May 24, 2018

4 Min Read
Long-term research shows cattle resist oral exposure to CWD
zixian/iStock/Thinkstock

Cattle fed extremely high oral doses of chronic wasting disease (CWD)-infected brain material or kept in heavily prion-contaminated facilities for 10 years showed no neurological signs of the disease, according to the University of Wyoming.

The University of Wyoming’s Wyoming State Veterinary Laboratory (WSVL), the Colorado Division of Parks & Wildlife and the Wyoming Game & Fish Department (WGFD) collaborated in the $1.5 million study. Results will be published in the July issue of the Journal of Wildlife Diseases. Details of the study are available here.

As part of the experiment, 41 calves were randomly distributed to WSVL, WGFD pens in Sybille Canyon in Wyoming and Colorado Division of Wildlife pens in Ft. Collins, Colo., while 18 were sent to the National Animal Disease Center in Ames, Iowa.

“It was an elegant experiment, in many ways,” WGFD wildlife disease specialist Hank Edwards said. “You were taking cattle and housing them with heavily infected CWD elk and facilities. If CWD was going to jump the species barrier, it was likely you would see something in these cattle that had laid out in the pens for 10 years. That’s a big deal.”

The late Beth Williams, a veterinary sciences professor at the University of Wyoming, initiated the study. Authors of the article continued the research after she and husband Tom Thorne were killed in a motor vehicle crash in 2004. Thorne had served as acting director of WGFD and also had conducted CWD research.

Authors of the article are Donal O’Toole, professor in the University of Wyoming department of veterinary sciences, which operates WSVL; Michael Miller, a veterinary epidemiologist with the Colorado Division of Parks & Wildlife; Terry Kreeger, a wildlife veterinarian with WGFD, and Jean Jewell, a molecular biologist with WSVL.

CWD is a contagious and fatal neurological disease affecting cervids — mule deer, white-tailed deer, elk and moose. An abnormal form of cellular protein, called a prion, in the central nervous system infects an animal by converting normal cellular protein into the abnormal form, the researchers explained. Brains show a spongy degeneration, with animals displaying abnormal behavior, loss of bodily functions and emaciation. The disease is among a group of diseases called transmissible spongiform encephalopathies (TSEs), which also include bovine spongiform encephalopathy in cattle and scrapie in sheep.

The long time span of the research is important, because CWD is a slow-acting disease, state WGFD veterinarian Mary Wood said. Even in deer or elk, it can take years for animals to succumb to the disease, she said. If the disease were to move into a different species, such as cattle, the timeline for infection to occur could be even longer.

“Many people are used to diseases moving quickly, but CWD doesn’t do that,” Wood said. “Nothing happens quickly, which is what makes this disease so insidious. It creeps up on you. It’s subtle. By the time you realize there is a problem, the disease is so widespread and established, it’s difficult to try to address.”

Some cattle can get a form of TSE when CWD material is injected directly into their brains, particularly when it is of white-tailed or mule deer origin, O’Toole said.

A more important question — and one Williams and collaborators asked — is: “What happens in cattle when you use a more real-life scenario involving oral exposure? Plus, we used high oral doses and heavily contaminated environments," O’Toole noted. "Cattle coming out of endemic CWD areas and slaughtered for human consumption are likely to pose no risk to people, based on the 10-year study and several earlier surveillance studies.”

That should be good news to livestock producers, Wood said.

“Managing disease in animals can be incredibly challenging,” she said. “It is even more challenging when the disease infects wildlife and is shared between wildlife and livestock.”

Wyoming cattle share the range with CWD-infected cervids, with CWD seen across almost the entire state, Edwards said.

“This research indicated CWD doesn’t easily transmit to cattle. Cattle do not get the disease due to a big species barrier, which helps restrict the disease to cervids,” he said.

Some Wyoming deer populations have 20-30% infection rates.

“We have few tools in the toolbox to manage the disease,” Edwards said. “We are trying different management efforts to hold the prevalence level, if not reduce the spread. That’s the big thing coming up next for CWD. How do we control it in our wildlife populations?”

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