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Chronic Wasting Disease: Risk ‘Very High’ of Transmission to Humans

U.S. News & World Report logo U.S. News & World Report 2/25/2019 Joseph P. Williams
a herd of animals standing on top of a grass covered field: Elk grazing in a green field in Alaska. © (Edwin Remsburg/VW Pics via Getty Images) Elk grazing in a green field in Alaska.

In the 1980s, Michael Osterholm was among a vanguard of public health scientists warning of a new, potentially deadly disease known as AIDS, and how gay men were at high risk. The next decade, he sounded the alarm about a mysterious neurological ailment showing up in cattle in the United Kingdom – nicknamed mad cow disease – and how scientific evidence indicated it could infect humans.

Now, Osterholm wants hunters and venison consumers to watch out for another disease that's been spreading and threatening members of the deer family in the U.S. and elsewhere.

Never mind the headline-grabbing, sci-fi nickname, he says: "Zombie" deer disease, scientifically known as chronic wasting disease, is a legitimate, potentially fatal public health threat that must be taken seriously.

"I think the risk is very high" that CWD could emerge in humans exposed by eating infected deer meat, says Osterholm, an epidemiologist, professor and director of the Center for Infectious Disease Research and Policy at the University of Minnesota. "I think there are steps that we could take today to minimize that risk."

According to the Centers for Disease Control and Prevention, chronic wasting disease is "a prion disease that affects deer, elk, reindeer, sika deer and moose" and has been found in Norway and South Korea as well as the U.S. and Canada. Signs of CWD in animals include lethargic behavior and dramatic weight loss, and testing has indicated primates can contract it by eating tainted meat, according to the CDC, raising concern that humans could, too.

But the disease is a cipher: It's fatal and untreatable, it may take a year or more before an infected animal develops symptoms, and some may die before showing them at all. That part of the puzzle – along with no evidence of human infections years after eating diseased venison – has kept some health officials from acting and the media from taking the issue seriously, Osterholm says.

In a recent conversation with U.S. News, he discussed the threat he says is posed by CWD and what can be done to guard against it. The interview has been edited for length and clarity.

Describe the scope of the problem: How widespread is it, and how fast is it spreading?

It is an immediate and very real problem in deer and elk in the United States – and potentially throughout the world in other species like reindeer and sika deer. It was discovered in 1967 in captive mule deer in Colorado. It's now in at least 24 states and two (Canadian) provinces and is spreading widely.

The Alliance for Public Wildlife, a group that has been very concerned about this, estimates between 7,000 and 15,000 chronic wasting disease-positive animals are being consumed annually in the United States, with that number likely to increase about 20 percent each year for the next three to five years. So clearly the magnitude is growing.

It seems your top concern is the possibility it might jump from deer to humans through the consumption of infected deer meat, like mad cow disease. How likely is that?

At this point, we don't know. And we have to be very honest about that. But there are far too many similarities with bovine spongiform encephalopathy (mad cow disease) in Britain, where we saw it in 1986 in bovines and it wasn't until 1996 when we identified the first cases in humans. During that time there was a tremendous amount of denial about whether it had become a human public health problem. You had agricultural officials who did TV spots with their children and grandchildren eating hamburgers on TV to show the public that the meat supply was safe.

Is the public, and are public health officials, taking this seriously? Have your comments, including testimony before Minnesota lawmakers, increased awareness of the problem?

I think we're starting to. First of all, we've got to get rid of this damn "zombie" label. I think it minimizes the issue of what's happening. And there's nothing zombie about this chronic wasting disease, any more than calling humans with neurologic disease zombies. It's just wrong.

Any time you have a situation like this, it's kind of like stages of death and dying itself. First thing you have to do is go through the recognition that something's happening. And I think the trend here has obviously been going in absolutely the wrong direction, with the very rapidly increasing number of infected (animals in the deer family).

The other thing is that CWD is one of those diseases that is difficult to follow up on in terms of (human) exposure and outcome because of the long incubation period – (it'd be) 10 years or more.

This is exactly what happened with (mad cow disease). I was one of those in the 1980s saying this concerns me greatly and that we need to take every step possible to eliminate these BSE-infected cattle from the food supply system in Europe. Many people in government, and particularly in agriculture, were very slow to take that up.

To date, CWD has really been handled largely as a wildlife-management issue. It has not been handled as a human health issue.

Why haven't public health officials stepped up?

Because there haven't been any cases, and so of course we tend to wait. This is one of the challenges of a disease like this, particularly when the incubation period is potentially so long.

Remember, if we were going to see cases in humans in 2019, these would have been people who were exposed back in 2005 to 2009. And there were very few animals back then that were infected. I have every reason to believe that it's going to get much worse in the wildlife.

What's being done to fight CWD? Are animal control agencies responding?

The control measures still are far from complete when you consider the transmission that's occurring right now. And once this gets ceded into an area, in the wildlife population or in the deer or elk, this is very difficult to get out.

I think Minnesota has done as good a job as any in the country and they're still having a real challenge. We just had a brand new location turn up positive in north-central Minnesota. And it was in association with a game farm that had positive animals.

How should we be fighting it?

If I was the benevolent dictator of chronic wasting disease, I would virtually try to eliminate game farms. They've demonstrated time and time again that they can't be assured to be good citizens in terms of trying to stop the transmission of this prion.

I (also) would do everything I could to make sure we had a highly sensitive, easy-to-use test for chronic wasting disease that could be used in the field. You'd know right there on the spot: Is this animal infected or not?

So you're simply advocating for hunters to be careful and test their meat.

This is not rocket science we're talking about here. It's a straightforward risk analysis of what we've experienced in the past with prions, what's happening now with whitetail deer and elk in America, what might very well be a scenario that could unfold tomorrow or in 10 years from now.

We're just asking, "Do you really want to eat an animal from a geographic area where we know (deer) have chronic wasting disease? Only to learn later these prions could be transmitted to humans?"

Given your experience with AIDS and mad cow disease, it seems like you're reliving the same experience again with CWD. Is it frustrating to believe you're ahead of the curve?

I recall getting booed off the stage multiple times talking about the early days of HIV/AIDS in social and business groups, gay men's groups. They thought I was scaring the hell out of them needlessly, back in '83 and '84. I wrote a book in 2000 about bioterror, why it was going to become a huge problem. I think I bought eight of the 12 copies that were sold in 2000. After 9/11, it became a New York Times best-seller. I've been here before.

My job as an epidemiologist is not to be a historian and record history. My job as an epidemiologist is to be an interventionist and change the future.

Video: What Is Zombie Deer Disease? (Provided by Daily Motion)

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