How to control chronic wasting disease

A fatal, incurable disease similar to mad cow disease has infested North American deer populations and is beginning to spread around the world. First identified in captive mule deer herds in Colorado in 1967, Chronic Wasting Disease (CWD) has now been found in captive wild mule deer, white-tailed deer, elk, moose, and reindeer. 32 states And across the border Canada, South Korea and Norwayamong other countries.

James Provost (CC BY-ND)

Veterinary microbiologist Nicholas Haley

The disease is caused by an abnormal protein called a prion, but it has not yet been seen to infect humans. Although concerns remainBut even if that doesn't happen, CWD could kill so many deer that it could wipe out populations. Wildlife officials could then institute stricter hunting rules, and fears of tainted meat could scare off potential hunters, affecting the roughly $23 billion U.S. deer hunting industry.

Since CWD emerged, scientists have been working to understand the disease and how it can be controlled. Over the years, three potential mitigation strategies have emerged, but each comes with significant challenges. Nicholas Haley, a veterinary microbiologist at Midwestern University in Arizona, said: Overview of Chronic Wasting Disease In 2015 Annual Review of Animal Biosciences I've been working on that problem ever since. Nouable Magazine He and Haley discussed the options and whether the disease can be contained.

This conversation has been edited for length and clarity.

What are prion diseases?

CWD is not caused by bacteria or viruses, but rather occurs when a natural protein in cells is mutated.

Kurt Vonnegut's novels Cat's Cradle Describes the discovery of new forms icePrions are solid even at room temperature. The book says that if a prion touched water, it would cause all other water to crystallize as well, freezing all the water on Earth. That's what happens inside the body. Animals are exposed to prions, usually through ingestion, and when a prion encounters a normal prion anywhere in the body, the abnormal protein convinces the normal protein to ingest it. Misfolded shape.

This is especially dangerous in the central nervous system because these proteins can form plaques that kill cells. Eventually, enough cells die and nervous system failure occurs. The animal begins to behave abnormally and eventually dies.

During that time, the sick animal can spread the prion to other animals through saliva, urine, feces, etc. Prions are very durable and can remain on plants or in the soil until another animal comes along and eats them.

Prion diseases, such as chronic wasting disease, spread when misfolded proteins help other proteins misfold. Here's how it works: A: A misfolded copy of the prion protein (green box) enters a cell or tissue. B: A normally folded copy of the same protein (blue circle) encounters the misfolded protein. C: The misfolded protein causes normal proteins to also misfold, leading to an accumulation of such proteins. D: The harmful protein causes even more proteins to change shape. E: The misfolded proteins break off and infect other tissues or other animals.

Can we kill all the sick animals before the disease spreads further?

Unfortunately, this only works if done early. Just like a wildfire, the sooner you can put it out, the better your chances of preventing it from spreading. But if you allow CWD to persist for too long, eradication efforts may be ineffective.

New York state, for example, launched a large-scale cull operation after first identifying five or six CWD-positive deer in Oneida County in 2005. The operation appears to have been successful, and the state still tests animals for the disease to try to detect outbreaks early.

But when wildlife managers tried localized eradication in Colorado, they didn't seem to see any long-term effects from CWD. This could be because the infectious protein was in the area for so long that it was essentially baked into the land. The protein is surprisingly stable and can persist in soil for years. Or, new diseased deer from nearby populations could have moved into the now-vacant area. The deer don't show symptoms until the disease is advanced, but they likely shed prions into the environment before then.

So, if eradication is only truly effective in the early stages, are there other strategies that might help in places where CWD is already “established”?

My work is primarily focused on breeding CWD-resistant animals. It's not about curing the disease, but finding animals that don't get sick as easily. We work with a game deer farm. They own several properties and keep about 600-800 deer, where CWD has become common. We first identified CWD there in 2014, and within a few years, the chances of a deer on one of their properties testing positive for CWD had risen to about 60-70 percent.

They also did genetic testing on the animals. They found that 80 to 90 percent of deer carry a particular gene mutation, or allele, of the prion protein that appears to make them highly susceptible to infection. But this is only one of about five possible alleles in a deer. And some alleles appear to be more resistant to CWD than others.

Terry Krieger/USGS

Deer infected with chronic wasting disease become weak, as shown in the photo, and often show symptoms such as lethargy and reduced mobility, and eventually die from the disease.

why?

It's like a key and a lock: The infectious CWD prion is a key that fits very well into a very common lock, but different alleles make the lock slightly different and the key doesn't work as well. But we don't yet know exactly how all these interact.

Over time, we began to focus on two different “good” alleles, and we believe our ultimate goal is to use artificial insemination and other breeding methods to eliminate the alleles we know are bad and create a population of animals that only have the good alleles.

Would keeping only animals with good alleles prevent the spread of infection?

That might make it manageable. The animals with these better genetic mutations are much less likely to get CWD, but they don't seem to be immune. We've been putting more animals on the farm with better genetic mutations, and by the time they're hunted, fewer of them seem to be infected. One farm where we've introduced a lot of our bred deer hasn't had a single positive case in the last two or three years.

So selective breeding could be like a coronavirus vaccine. You could still get infected suddenly, but it would have a huge effect on slowing the progression of the disease and minimizing transmission. And at that point, we might have management tools that we can use to reduce transmission to essentially zero. Even if it takes these highly resistant animals five years to get sick, if they were all hunted by age three, CWD, for example, would eventually go away.

Once confined to a few counties in Colorado and Wyoming, chronic wasting disease has now spread to 32 states and several Canadian provinces, affecting both wild and farmed deer.

Does selective breeding work for captive animals as well as wild animals?

That's a really good question. This kind of selection happens naturally in wildlife. Natural selection favors resistant animals over time, but it does so much more slowly. In controlled situations, like when a local population has been completely wiped out by CWD, it's possible to release captive-bred animals. But releasing just one or two bucks would quickly dilute their genes.

And while there teeth Many wildlife experts are strongly opposed to this, as there is no precedent for raising animals on farms and releasing them into the wild. They want to keep wild populations wild. Introducing deer to farms would taint it in a way. And that's something that can't be reversed. I understand that point of view. Many wildlife people are more hopeful about vaccine research.

I know there are vaccines against viruses, but is it possible to make a vaccine against a protein?

We already do. For example, the COVID vaccine is specific to the spike protein of the COVID-19 virus, not the whole virus. And prions are just proteins. So the vaccine could theoretically work by creating antibodies that can bind to the prion protein, allowing the body to recognize and eliminate it.

But the problem with chronic wasting diseases is that, unlike COVID-19, healthy versions of the problematic proteins already exist naturally in the body. The challenge is to develop a vaccine that targets the unhealthy versions of the proteins without attacking healthy cells.

Developing a vaccine may also be difficult, depending on how the disease works in the body. Researchers in Wyoming have tested vaccines, injecting moose with one particular vaccine and finding that it kills them. They got sick sooner.

The idea is that white blood cells naturally kill invaders and then haul their remains home to the lymph nodes to teach the body what it saw and activate defenses. Getting a vaccine can speed up this process by making the white blood cells better able to detect and capture invaders.

But the problem in this case was that after the white blood cells picked up the prions, they couldn't destroy them — they were still infectious — so they just carried the prions to places where they could spread faster, in the same way that ants carry poison back to their nest and infect other ants.

I'm not saying the vaccine won't work, and there are groups working on this issue, so I want to be optimistic, but I have doubts about the vaccine.

And even if we do have an effective vaccine, we still need to figure out a good way to distribute it. Injecting it into wild animals is not practical. In the eastern US, they use a rabies vaccine in bait that can be dropped from an airplane. Hypothetically, such a vaccine might also work for CWD. But there are a lot of hurdles to overcome.

So, overall, how do you see the prospects for managing and containing CWD?

It really depends on how people react. Unfortunately, states are responding in different ways. Some are taking it very seriously, others are trying to sweep the issue under the rug. I expect that in our lifetime we will see a similar situation in every state in the U.S. except Hawaii.

And what happens after that? Do you think this will eventually go away, or will we just have to live with it?

I think it's the same as the coronavirus: it's never going to go away. It might not be as big a problem in 100 years, but it's still going to be around.

And let's pray that it doesn't jump on humans.

So yeah, fingers crossed even harder.

This article is reprinted from Nouable MagazineRead the original article here.