Short Wave - Why We Should Care About Viruses Jumping From Animals To People

Episode Date: April 3, 2023

The phenomenon of zoonotic spillover — of viruses jumping from animals to people — is incredibly common. The question is: which one will start the next pandemic? NPR science desk correspondent Michaeleen Doucleff brings us her reporting on Influenza D, an emerging virus spreading among cows and other livestock in the United States. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, Short Wavers. Emily Kwong here with Science Desk correspondent Mike Lean-Ducleff. Hi, Mike Lean. Hi, Emily. Welcome. Thank you. So typically you focus on global health, but your latest reporting brought you closer to our shores to the U.S.

Tell me what you found. This story, which is really fascinating to me, begins more than 10 years ago with a farmer in Oklahoma who had a bunch of sick pigs. Okay. Benjamin Hawes, who's a virologist, said these pigs had what looked just like the flu. Like a person with respiratory disease, you know, a pig that's labored breathing, maybe a runny nose, cough, potentially, a fever. Poor pig.

I know. Ben was watching these pigs because at the time he was working at Newport Laboratories. It's a company that develops vaccine for livestock animals like these pigs. They would isolate viruses from sick animals, grow the viruses in the lab, kill the viruses, and then make a vaccine with this dead virus. Wow, that is interesting work. How do you go about isolating a virus in a pig? Well, the farmer in Oklahoma took samples actually from the pig's noses. So almost just like the way you take a sample of yourself when you're taking an at-home COVID test. Yes, you swirl for 15 seconds. Is it something like that? Exactly, inside the little piglet. And then he sent the samples to Ben so he could figure out what was making the little pig sick. And Ben immediately thought that the pigs had just the regular flu virus. We expected influenza A. That'd be the most common thing.

So that's the virus that often causes the flu in people. But when Ben and his colleagues grew the virus in the lab and looked at it underneath the microscope, they quickly realized they were wrong. Ben was actually shocked by what he saw. What is this thing? We've never seen anything like this before. And our concern was, you know, is this something that we should be worried about getting into people? Today on the show, with the discovery of an entirely new influenza virus, spreading among pigs and other animals, means for us humans. I'm Emily Kwong. I'm Michael Educliffe. And you're listening to Shorewave from NPR. Okay, so, Michael, in, the COVID pandemic has forced a lot of us to confront the reality of zoonotic spillover.

viruses that can jump from animals to people, which the CDC says is true of three out of four emerging viruses. That's a lot. Yeah, that's a pretty shocking statistic, Emily. But here's actually the real shocker. In the last few years, scientists have started to realize that these new animal viruses are jumping into people every day, many times a day. Oh. One scientist said that they're kind of like snow falling across humanity. Oh, dear. I was talking to Stephen Goldstein about this. He says these spillover events, they aren't extremely rare at all.

I mean, we know this because when people start looking, people find it. He's an evolutionary virologist at the University of Utah. And for instance, he says one study estimated that in Southeast Asia alone, an animal coronavirus jumps into a person every eight minutes. This is a lot. Okay. Okay. Snow falling across humanity.

Yeah. All right. What kinds of viruses are jumping from animals to people, which are the most common? So there's a whole bunch of them, but some like to do it way more than others. And at the top of the list is coronaviruses. They love to jump into people. And the other big group are influenza viruses. Those are the big ones.

And right now, doctors and scientists don't know much about these viruses at all because they masquerade as regular colds, flus, or even pneumonia's. Look at it this way, Emily. Say you have a respiratory infection and it gets so bad that you go to the hospital. Sometimes the doctor will do a bunch of tests to see what's wrong, right? Yeah, yeah, yeah. Like, is it strep throat? Is it the flu?

That kind of thing. Exactly, exactly. Well, those tests can only identify the cause of the respiratory infection about 40% of the time. Oh, yeah. I hadn't really thought about that. We don't always know what's making us sick. But when you put it this way, in the context of zoonotic spillover, like what is causing the other 60% of infections?

Yeah, it's a huge question that no one really talks about much, right? But many scientists are starting to realize that that other 60% is likely these animal viruses that are jumping into people cryptically. So for instance, scientists recently found a new coronavirus that's causing pneumonia and children in both Malaysia and all the way across the world in Haiti. It likely comes from dogs, and there's evidence a similar virus has caused flu-like symptoms in adults in Arkansas and Thailand. Another example is this new virus that Ben found in the pigs, right?

Yes, you were telling us about this mystery virus on that farm in Oklahoma affecting all those little pigs. Yeah, so Ben and his colleagues grew the virus in the lab, and after a few days, they realized they had stumbled upon an entirely new influenza virus. It's now called influenza D, and it's completely unrelated to the flus known to infect people. D is a completely different from influenza A and B. That's Varalges Fong Lee at the University of Kentucky. He co-led the discovery of influenza D. Once he and others started looking for signs of influenza D in other animals, they found it nearly everywhere they looked, and sheeps, goats, camels, horses. So influenza D is really making the rounds, at least among livestock.

Yeah, it's a very promiscuous virus, but they hit the jackpot when they looked at one particular animal, cows. From California all the way to Vermont, from North Dakota, all the way to Texas. That is a big range. That is a lot of cows. How is the virus then impacting the people who work closely with the virus? These animals, and specifically cows, I'm thinking about dairy farms and ranches. Yeah. Do we know?

You know, we really don't know. Researchers are just starting to look at that. Okay. One of them is Jessica Liebler at Boston University. She's an environmental epidemiologist there. And in 2019 and 2020, she and her colleagues ran a small experiment, very simple. They went to five dairy farms in the southwest and washed out the workers' noses before and after their shifts on the farm. And then they looked for influenza D inside those washes.

We found about two-thirds of the participants were exposed at some point during our study period. You looked at only 30 people in five days, and yet you found it very easily, right? So does that suggest that it's pretty common in these environments? To me it does. To me, it suggests that if you look for it, you probably will find it. So if the virus were rare on the farms, right, then finding it at such a high level, by chance would be really unlikely. Other studies actually looked for signs of infections in cattle workers in Florida.

Specifically, the study tested for influenza D antibodies inside the worker's blood. They found really, really high levels. More than 90% of the workers had antibodies to influenza D, which implies that not only were they exposed, but they were also infected. This is interesting because it's kind of two different ways to monitor for virus. You have the blood test with the antibodies, but you also have the nose washes. Yes. Can you draw the distinction between them, like the difference between being infected versus being exposed?

Yeah, absolutely. So when you're exposed to a virus, it means the virus is coming into contact with you, right? On your skin and your nose and your mouth. And this gives it a chance to infect you. An infection is when the virus goes farther than that and actually gets inside your cells and typically causes damage, and that often will trigger an immune response. So 90% of the cattle workers that they looked at in Florida had antibodies against influenza D and had likely been infected, right?

In contrast, they also looked at people who didn't work on farms, and only 18% of those people had influenza D antibodies in their blood. So clearly something is going on here with these farm workers and influenza D. Yeah. And this influenza D. in farm workers, is it making them sick? Do we know? We don't know. Nobody has looked really yet. There's no evidence it's making them sick. And, you know, it's not likely making them really sick because doctors and scientists would have picked it up. But altogether, Jessica says,

these studies show that influenza D is likely what's called an emerging virus. It's jumping into people regularly who work with animals, such as these dairy farmers, but it's not likely spreading beyond them. This doesn't seem to be something right now that the general public is exposed to in a large way, but is something that seems to be of concern for this smaller group of frontline workers who are occupationally exposed to food animals, specifically cows and pigs. She also says it could become a concern for the general public, and that's because there's a real risk this virus could adapt to people as more and more workers are infected.

Influenza viruses mutate rapidly and frequently, and there is a risk as more humans are exposed to this virus that it can evolve to be transmitted among humans from person to person and also develop more virulence, so causing more symptoms in people. You know, making people sicker, right? Yeah, this here seems like the key piece to me. Yes. You've described this whole.

chain of events leading to this understanding of this emerging virus influenza D. What is the value of catching a virus like this early, of knowing what it is and maybe how it spreads? Yes, Emily, this is really the key part of this piece. And what scientists are realizing is that viruses like this, these emerging viruses that are regularly jumping into people over and over again, these are likely the viruses that are going to cause the next pandemic, the next big outbreak. For instance, Scientists think that at some point in time, Emily, SARS-CoV-2 or a virus related to SARS-CoV-2 was in this phase, that it was jumping into people regularly, maybe making them a little bit sick, but nobody noticed it. And just think, like, what would have happened if scientists had caught SARS-CoV-2 in that stage where they could study it and make treatments and vaccines for it before it became, you know, deadly and, you know, very, very contagious. Yeah.

I was talking to Stephen Goldstein about that. at the University of Utah. And he says that studying these viruses, these emerging viruses, is really the key to stopping the next pandemic before it occurs. And he says scientists should focus their effort and their time and their money on these viruses that are already getting inside people

instead of just cataloging all the viruses that are in wild animals. Cataloging viruses in wildlife is interesting from a scientific standpoint, I think, but from the standpoint of like predicting pandemics, I think it's a ridiculous concept. We need surveillance, active surveillance, in the humans and also in, like, domestic animals. So then my last question before we go is, you know, widespread virus surveillance in domestic animals.

Is anyone doing that yet in the U.S.? Yeah. So for all viruses, it's a little tricky to answer because a lot of that information is kept from the public by the farms. One company, Cambridge Technologies, is working on a vaccine against influenza for animals. but again, very few farms are looking out for it in animals or workers. I reached out to the National Cattlemen's Beef Association, the lobbying group for cattle ranchers for a comment. A spokesperson referred us to the U.S. Department of Agriculture.

The USDA, along with the Centers for Disease Control and Prevention, said in emails, at this point, there isn't any evidence that influenza D is causing significant harm to livestock, so there aren't currently any surveillance systems in place for livestock or for workers. Seems like a chicken and egg problem. Exactly. Like there aren't resources until there's an issue, but when a virus is harbored in an animal,

being passed among animals, it can mutate and change and become more virulent and once there's an issue. Exactly. That's what Jessica Liebler kept pointing out to me. She said officials and scientists had a similar view of coronaviruses for a long time. You know, they thought they weren't a major concern because they only caused the common cold,

so they kind of brushed them off is not really that important, until one day, one of them changed and made the whole world pay attention to them. Mike Lean, Ducleff, thank you for reporting kind of from the front lines of emerging viruses and just telling us how pandemics start. It's been really interesting to talk to you. Thank you so much for your interest and for having me on. This episode was produced by Margaret Serino. It was edited by our managing producer Rebecca Ramirez and producer Liz Metzger. It was fact-checked by Britt Hansen.

Our audio engineer was Margaret Luthar. Brendan Crump is our podcast coordinator. Beth Donovan is our senior director of programming, and Anya Grundman is our senior vice president of programming. I'm Emily Kwong. I'm Michael Lee-Ducliff. And thank you for listening to Shortwave from NPR.