A new flu is spilling over from cows to people in the U.S. How worried should we be?
MICHEL MARTIN, HOST:
More than three years after COVID-19 was declared a pandemic, scientists are finding that viruses regularly jump from animals to people. It's happening with other coronavirus infections in Malaysia and Haiti. And now, in the U.S., scientists may have detected a new threat from an influenza virus that jumps from livestock to people. NPR's Michaeleen Doucleff has the latest in our series on emerging viruses.
MICHAELEEN DOUCLEFF, BYLINE: Back in 2011, a farmer in Oklahoma noticed something wrong with his pigs. The little animals were just a few months old, and they had what looked like the flu.
BEN HAUSE: Just be like a person with respiratory disease - you know, a pig that's - labored breathing, maybe a runny nose, cough, potentially a fever.
DOUCLEFF: That's Ben Hause, who worked with the farmer. He's a virologist, and at the time, he was at a biotech company.
HAUSE: An animal health company called Newport Labs.
DOUCLEFF: The company figures out what's infecting animals on a farm and then makes customized vaccines against it. So this farmer in Oklahoma took a little swab from a pig's nose. Then the farmer sent the sample to Hause. Right away, Hause thought the pig had your run-of-the-mill flu virus.
HAUSE: We expected influenza A. That'd be the most common thing.
DOUCLEFF: That infects animals and people. When you get a flu shot, that's against influenza A. But when Hause grew the virus in the lab...
HAUSE: Our concern was, we've never seen anything like this before. What is this thing?
DOUCLEFF: The pig was infected with an entirely new type of flu virus. It's now called influenza D. And once they started looking in other animals across the country, they found signs of influenza D everywhere - in sheep, goats, horses and, most predominantly...
FENG LI: Cattle.
DOUCLEFF: That's Feng Li. He's a virologist at the University of Kentucky and co-led the discovery of influenza D. He says the virus is incredibly common in cows. When researchers measured the percentage of cows that have had the virus, it was super high.
LI: Way high, which is really surprising.
DOUCLEFF: They estimate that 45 to 85% of cows have been infected, and not just in Oklahoma, but across the whole country.
LI: From California all the way to Vermont, from North Dakota, all the way to Texas.
DOUCLEFF: So then the question became, if this virus infects so much livestock, does it infect the people who work with them? Jessica Leibler is an environmental health expert at Boston University and has been investigating this. In 2019, they went to five dairy farms in the Southwest and looked for influenza D virus inside the noses of workers there.
JESSICA LEIBLER: In the United States, this is largely a low-income, in many places, immigrant workforce.
DOUCLEFF: Leibler only looked at 31 workers over five days, but she found a high rate of exposure to the virus.
LEIBLER: We found about two-thirds of the participants were exposed to influenza D at some point during our study period.
DOUCLEFF: 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?
LEIBLER: To me, it does. To me, it suggests that if you look for it, you probably will find it.
DOUCLEFF: Now, Leibler was just looking at exposure, but other studies have shown the virus has the ability to go even farther. It can invade cells and trigger an immune reaction. Specifically, they found antibodies against influenza D in the workers' blood.
LEIBLER: 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.
DOUCLEFF: All together, this suggests that influenza D is what scientists call an emerging virus. It regularly jumps into people who work with cows. Right now, there's no evidence the virus makes people sick or it can spread from one person to another. But there's a concern, Leibler says, the virus could change.
LEIBLER: 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.
DOUCLEFF: For decades, scientists thought these emerging viruses were rare, that animal viruses hardly ever jumped into people. But Stephen Goldstein at the University of Utah says scientists are just starting to realize that's wrong.
STEPHEN GOLDSTEIN: I think it's clearly not extremely rare. I mean, we know this 'cause when people start looking, people find it.
DOUCLEFF: In fact, there's likely a whole group of animal viruses making people sick all over the world, viruses that doctors don't know anything about out because they masquerade as regular colds, flus or even pneumonias. At some point, a virus related to SARS-CoV-2 was likely in this phase. So scientists are starting to think that these are the viruses, like influenza D, that have the potential to cause the next pandemic. Until now, Goldstein says, scientists have been looking for these emerging viruses, primarily in wild animals. But he says this is not an efficient strategy. Animals carry millions of viruses, and most of them will never infect people.
GOLDSTEIN: 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.
DOUCLEFF: Instead, he says, scientists need to focus on viruses that have already made the jump. And to do that...
GOLDSTEIN: We need surveillance - active surveillance - in the humans and also in, like, domestic animals.
DOUCLEFF: Right now, very few farms are looking out for the virus in animals or workers. I reached out to the National Cattlemen's Beef Association, the lobbying group for cattle ranchers, for comment. A spokesperson referred me to the U.S. Department of Agriculture. The USDA, along with the Centers for Disease Control and Prevention, said in emails that 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 workers. But Leibler points out that is similar to how officials viewed coronaviruses years ago. Since the viruses were causing little harm, it was easy to just ignore them until one changed and made the whole world pay attention.
Michaeleen Doucleff, NPR News.
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