Chronic Wasting Disease Vaccine Fails Elk Test

The state wildlife veterinarian told Wyoming Game and Fish commissioners that a vaccine to fight Chronic Wasting Disease appears to have failed in a test among live elk.

Dr. Mary Wood cautioned that her findings are preliminary, that they haven’t been peer-reviewed or published, and that there is a hiccup in the study. Nevertheless, she said the live tests revealed a statistically significant difference showing the vaccine to be ineffective.

“We have not observed a protective effect associated with this vaccine,” she stated in a PowerPoint presentation to the commission. “There may be a negative effect associated with this vaccine,” she said, with inoculated elk about seven times more likely to develop CWD.

Thirteen surviving elk will continue to be studied in the test, she said. The trial also may help researchers better understand how genetic differences make some elk less susceptible, possibly immune, to the disease.

The news from Wood came as Game and Fish said it has found the incurable, always-fatal disease in several new deer hunt areas and a new elk hunting area. The new areas document the neurological disorder spreading farther west across the state. In 2014, Game and Fish discovered 83 mule deer, 12 white-tailed deer, and 15 elk that tested positive for CWD.

However, no elk have yet been found with CWD west of the Continental Divide where the state operates 22 winter elk feedgrounds. Some people are fearful the withering affliction would spread rapidly once it arrives where elk are concentrated artificially.
Results are disappointing, but helpful

Wildlife managers hoped the vaccine might help contain CWD that’s infected deer and elk across wide parts of eastern and central Wyoming. Made by the Canadian company Prevent, the recombinant protein fusion vaccine had shown potential. “They actually did some studies with domestic sheep and [deer-family] cervids,” Wood told the commission. “It looked very promising. They had thought this vaccine might either protect against actual infection of CWD or potentially it might prolong survival.”

But now, almost three years after the trial on 38 elk started at the agency’s Tom Thorne and Beth Williams Wildlife Research Center, the results show otherwise. “I don’t have the greatest news to give you today,” Wood told the commission Nov. 6. “I have not found the magic bullet to treat CWD.”

Chronic Wasting Disease is a malady akin to Mad-cow Disease in cattle and Creutzfeldt-Jakob Disease in humans. It causes neurological degeneration, but there’s no documentation of it spreading from animals to humans. Protein-based infectious agents called prions cause the disease.

In the research setting, infected elk first begin showing changes to their temperament. They appear dull and lose general awareness. They begin to waste, drool, don’t shed winter coats, and start to shake.

Wood showed slides and videos of infected elk, warning commissioners that they were difficult to see and watch. “This really is an ugly disease,” she said.

Regardless of the preliminary findings, there are no immediate plans to change the state’s strategy regarding CWD. Today, that includes testing of hunter-killed animals along the advancing front of the disease. Sick and dying animals that are euthanized also are tested. The effort involves a separate surveillance drive in the Jackson Hole area where lymph nodes of many hunter-killed elk are collected and analyzed.

Also, on some of the state’s 22 feedgrounds, Game and Fish workers practice low-density feeding in an effort to reduce the spread of diseases. Game and Fish will be proposing an update of its CWD strategy later this year, Chief Game Warden Brian Nesvik said. When it is released for public review, it likely will include a call for removal and incineration of any carcasses on feedgrounds or any carcass of any animal that tests positive, Nesvik said.

The news about the vaccine reinforces calls for predators to play a larger role in the ecosystem and for an end to supplemental winter feeding, said Lloyd Dorsey, conservation director for the Wyoming chapter of Sierra Club in Jackson.

“We do have tools at hand to address this disease, this enormous threat to our big-game herds,” he said. “That is the conservation of predators. Increasing the number of predators would better insure the health of those deer and elk herds.”
More predators would be able to target more withering animals, helping contain the disease, Sierra Club believes. But Wyoming’s plan for wolves calls for limiting numbers to about 15 breeding pairs and 150 individuals outside Yellowstone National Park. In about 80 percent of the state, wolves can be killed at will under Wyoming’s plan, a plan that’s been suspended because of a court ruling.

Sierra Club and other groups also criticize the state’s feedground system. Having too many elk for the carrying capacity of the habitat also is bad practice, conservation groups say. At the National Elk Refuge next to Jackson, for example, a plan to reduce the number of elk being fed there every winter has not yet been achieved.
The live-animal trial

Wood outlined results from a “live animal trial” that began in 2013 with female elk calves captured on the Game and Fish South Park Feedground near Jackson. The trial was to start with elk that were not already infected with CWD.

“We do feel confident the elk we got for this study were negative for CWD,” Wood told commissioners. There’s no easy way to test a live elk for CWD.

The trial saw half the group inoculated with the vaccine while the other half would serve as the control group. Researchers accounted for genetic variances they believe make some elk less susceptible to CWD. The experiment took place at the research center at Sybille Canyon near Wheatland.

Wood admitted to a hiccup in the test, however. Elk were held in the infected Sybille pens for up to 20 days before the vaccine was first administered. “There is potential there might have been some level of exposure prior to vaccination, so that definitely is a big drawback for our study,” Wood told commissioners. Ideally, the vaccination would have been given before exposure at Sybille.

“We like to control for every variable,” Wood said in an interview. “The reality is research is somewhat messy.” Once the live trials are concluded, the peer-review process will determine the significance of the flaw and whether the study should be published, Wood said. That could happen in about a year.

“Still, we have a statistically significant difference between groups,” she said. Nesvik agreed. “Despite that error, it still is going to be pretty compelling evidence this vaccine wasn’t the answer,” he said. Wood first presented the preliminary findings at a gathering of the U.S. Animal Health Association a few weeks ago.

“We thought it was important for the research community to just be aware of our preliminary work so they can take that into consideration as they move forward with other vaccines,” she said. “This does not mean there are not opportunities for other vaccines.” The result could help disease researchers, if only to spur them to look in different directions. “A negative result is still positive progress,” Wood told Game and Fish commissioners.

Nesvik cautioned patience. “No silver bullet ever gets developed without a pretty long series of studies,” he said. “We’re going to learn a lot from this. It’s going to inform the next study.”
All the elk were exposed to CWD at pens at Sybille. That facility is contaminated with CWD, which is nearly impossible to cleanse from a site. The control group of elk was inoculated with a benign saline solution in an effort to ensure those animals endured the same amount of stress as ones with the vaccine.

Researchers documented the onset of the disease in the animals. In July, 11 of the vaccinated were infected while only 4 of the control group were sick with CWD, Wood’s presentation showed. Vaccinated elk died an average of 58 days sooner than the control group. The testing of live animals for infection is complex and limited. It requires taking a biopsy of rectal tissue, which can only be done a few times.
Hunters not so worried

While Sierra Club and others would see more predators and fewer elk, Game and Fish has to take hunters into account, Nesvik said. Game and Fish believes elk will persist even if CWD infection reaches feedgrounds. “All of the predators certainly have a place in the ecosystem and the landscape,” he said. “It’s a balance.”

Hunters won’t necessarily be turned off by the potential of shooting an infected elk either, Nesvik said. The Centers for Disease Control believes the chance of cross-species infection is low. CDC and the World Health Organization say parts or products from any animal that looks sick or tests positive for CWD should not be eaten. Game and Fish recommends not moving animal spines and brains out of an area that’s known to be infected.

Anyone can get a harvested elk or deer tested for a fee at the Wyoming State Veterinary Laboratory, 1174 Snowy Range Road, Laramie (307) 766-9925.

“We’ve seen an increase in hunting in the eastern part of the state where CWD is prevalent,” Nesvik said. “I don’t believe that [CWD] would force our demand or interest in hunting to go down.”

News of Wood’s study came as Game and Fish documented new deer and elk hunt areas where CWD-infected animals have been found. “One of those is going to be a deer area near Cody, another on the Wind River Indian Reservation, a deer area in the Black Hills and an elk area in the Snowy Range,” Nesvik said.

“My reaction to that — it’s not anything real surprising,” he said. The newly discovered infected hunt areas are near other infected areas and the spread was anticipated. “Nothing [new] has moved to the other side of the Continental Divide.”

It is important Wyoming continue to research ways to combat CWD, he said. “I think we’re going to figure out some day how to mitigate the effect on cervids.”

As a veterinarian, Wood said, she strives to keep wildlife healthy. “I have no tools right now to treat or prevent CWD.”

Source Link: