Chronic wasting disease has been around for decades, but its recent spread has health experts worried.

Deer hunting seasons across the US have begun, and with that, comes new warnings of chronic wasting disease—or, the terrifying-sounding "zombie deer disease."

As of August, the Centers for Disease Control and Prevention have identified at least 277 counties in 24 different states with reports of chronic wasting disease in free-ranging deer, elk or other cervids (aka ruminant mammals). Now, some states, including Nevada, are hoping to continue to stay disease-free.

According to the Nevada Department of Wildlife, hunters are urged to visit mobile sampling stations for the disease. Those in Nevada are also not allowed to bring in wildlife carcasses from other states.

Earlier this year, media attention increased around chronic wasting disease after Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told state lawmakers that he’s concerned that this infection may spread to people.

“It is probable that human cases of chronic wasting disease associated with consumption with contaminated meat will be documented in the years ahead," Osterholm told the Minnesota legislature last week, as reported by NBC News. "It’s possible the number of human cases will be substantial and will not be isolated events.”

In light of this new development, Health spoke with Brian Appleby, MD, director of the National Prion Disease Pathology Surveillance Center at Case Western Reserve University. Here’s how he describes this illness and its spread throughout the United States, plus how worried he thinks we should be.

What is chronic wasting disease?

This so-called zombie deer disease—which is related to bovine spongiform encephalopathy (BSE), also known as mad cow disease—gets its nickname from the symptoms it causes. A year or so after an animal becomes infected, according to the CDC, it can begin stumbling and acting listless and confused. Infected animals can also lose weight rapidly, hence the “wasting” part of the disease’s name.

Chronic wasting disease (CWD) is a prion disease, which means it’s caused by proteins (called prions) that attack the brain and spinal tissue. BSE is also a prion disease, as is a human illness called Creutzfeldt-Jakob disease (CJD). In deer and elk, CWD spreads through bodily fluids, either directly or through contamination of soil, food, or water.

There’s no treatment or cure for CWD, and it’s fatal to animals who become infected. Some animals develop the telltale symptoms listed above, while others die without developing any symptoms at all.

Should humans worry?

While the spread of CWD is concerning—especially for hunters and wildlife conservationists—Dr. Appleby says there’s no cause for panic just yet. “Number one, this is not necessarily a new thing; it’s something that’s been going on for many years,” he says. “And number two, we don’t have any evidence that it’s transmissible to humans.”

Other types of prion disease, specifically one type of BSE, can be transmitted to humans who eat contaminated animal meat or other tissue. Infected humans don’t get BSE, but they do develop a similar (and also fatal) condition called variant Creutzfeldt-Jakob disease (vCJD).

This is rare, with only four cases ever reported in the U.S.—all of which are believed to have originated outside of the country. And there are zero reported cases of a human getting sick from eating contaminated meat from cervids (members of the deer family), although studies done on monkeys have shown that chronic wasting disease can pose a risk to other animals who come into contact with meat or brain material from infected animals.

The biggest worry right now, says Dr. Appleby, is the amount of uncertainty surrounding this issue. “Not only do we not know if transmission to humans is possible, but we also don’t know what that would look like,” he says. “Most prion disease tends to look fairly similar, but really the only way to know where a disease is coming from is to look at the brain tissue.”

The spread of CWD is also concerning because it’s occurring in wild animals, says Dr. Appleby, as opposed to BSE outbreaks that occasionally happen in domesticated cattle. “With cattle or sheep or goats, you can cull those animals and that helps with containing the [disease],” he says. “It’s a little different with cervids because they’re free-ranging and you don’t have the luxury of being able to contain them and stop the spread.”

That’s why constant monitoring of prion diseases is important, he says. The U.S. Department of Agriculture monitors cattle for BSE, but the CDC is also monitoring other types of disease—including CWD in deer and elk. Dr. Appleby’s center also studies human cases of CJD, to determine whether they came from contaminated meat and are evidence of a new outbreak or if they arose spontaneously.

How can we protect ourselves?

Even if there’s no evidence that CWD transmission to humans is possible, many experts believe it’s better to be safe than sorry. “Since 1997, the World Health Organization has recommended that it is important to keep the agents of all known prion diseases from entering the human food chain,” reports the CDC.

And eating meat from contaminated elk or deer is a real concern. According to a 2017 Alliance for Public Wildlife report, an estimated 7,000 to 15,000 CWD-infected animals are consumed annually by hunters and their families. That number likely grows by about 20% a year, the report states, because the disease has spread so much in recent years.

Hunters and people who consume wild game can take precautions by getting their meat tested for CWD, says Dr. Appleby. Procedures and facilities vary by region, but several states have set up free testing centers, according to NBC News. The CDC also recommends avoiding deer or elk that look sick, act strangely, or are found dead.

When field dressing a deer, hunters should wear latex or rubber gloves, avoid using household knives or kitchen utensils, and minimize how much they handle the animal’s organs, particularly the brain and spinal cord tissue. And for people who have their deer or elk commercially processed, the CDC recommends asking the facility to avoid mixing meat from multiple animals.

Dr. Appleby agrees that these steps are a good idea, even if no humans have gotten sick from CWD so far. “Obviously we don’t think that it’s a good thing for people to eat any kind of meat that could be contaminated with a prion disease,” he says. “Take advantage of these testing services, take precautions, and don’t put yourself at risk.”

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