Research suggests CWD vaccine for deer possible

Pittsburgh — Researchers believe they may have taken the first step toward developing a vaccine for chronic wasting disease.

Don’t expect to see treatments any time soon, though. They also say it might be years before the vaccine exists in a practical form, especially as it relates to wild, free-ranging deer.

According to a paper published in “Vaccine,” a medical journal, scientists from NYU Langone Medical Center, Colorado State University and elsewhere began with 11 “CWD naïve” farm-raised deer. Six deer were left untreated as a control group. 

Five were given the vaccine, which was made using Salmonella bacteria, “which easily enters the gut, to mirror the most common mode of natural infection, ingestion of prion-contaminated food or feces.” 

All were then exposed to wasting disease and monitored over time under conditions meant to simulate free-ranging whitetails.

The result?

All six deer that went untreated contracted the disease and died. Four of the five given the vaccine contracted it, too, though it took about 300 days longer, on average, for them to come down with it.

The fifth deer did not – and to this day has not – gotten CWD.

Researchers called that a “partial success.”

“Our reported results show for the first time that protection from exogenous prion infection is possible in a species naturally at risk for infection,” the authors wrote in the paper.

Two went even further, saying the vaccine could perhaps have human prion disease applications some day.

“Although our anti-prion vaccine experiments have so far been successful on mice and deer, we predict that the method and concept could become a widespread technique for not only preventing, but potentially treating many prion diseases,” said lead study investigator Fernando Goni of NYU Langone.

“Now that we have found that preventing prion infection is possible in animals, it’s likely feasible in humans as well,” said senior study investigator and neurologist Thomas Wisniewski, also of NYU Langone.

Justin Brown, veterinarian for the Pennsylvania Game Commission, issued a few words of caution, though.

While calling the study “good science,” he also warned that the way in which it was conducted shows how far away any real-life application of a vaccine might be.

The deer initially given an oral dose of the vaccine were given eight boosters over 11 months. That often involved giving them anesthesia and “painting” the vaccine on their tonsils and rectums, Brown noted.

That’s not something that could be replicated in the wild, he said.

“I think it’s promising. And we want to do this research. But only one of six animals looks like it was completely protected, and that under some specific circumstances,” Brown said.

Researchers addressed the idea of treating wild deer with the vaccine. In their paper, they proposed treating wild deer by putting out baits containing the vaccine. Salmonella, they wrote, “can be stable for months when dried under certain conditions and mixed with food.”

“Thus, it would be possible to dose individual deer in a free-range herd repeatedly, using food pellets containing vaccine Salmonells left in the environment at appropriate times, given the known tendency of herds to return to the same foraging grounds at regular intervals.”

Wisniewski added that “if further vaccine experiments prove successful, a relatively small number of animals (as few as 10 percent) could be inoculated to induce herd immunity, in which disease transmission is essentially stopped in a much larger group.”

That’s not entirely unfeasible, Brown cautioned again, but added that “it’s a big jump” to go from treating deer in a pen to treating deer in the wild in that way.

“When you’re talking about how applicable this is, it’s still a ways off,” Brown added.

There’s one other thing to consider, he said.

Four deer treated with the vaccine eventually contracted CWD, albeit 300 or so days later than the non-treated ones.

Were they, Brown wondered, shedding prions all that time? If so, rather than the vaccine helping, it may have only allowed those sick deer to spread the disease for a longer period of time, presumably over a wider area if they had been in the wild.

In that kind of case, the vaccine might actually contribute to the spread of the disease to a greater portion of a herd, he said.

Researchers, though, called the vaccine a “step in the right direction.”

“Even if such a vaccine gave only partial protection from CWD, increasing the herd immunity would inhibit the current rapid spread of CWD, thus reducing the zoonotic potential,” they wrote in their study.

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