MAGGIE KOERTH: This is Science Friday. I’m Maggie Koerth. During the last few weeks, you may have heard about an alarming case of avian flu that’s jumped from wild birds, to poultry, to cattle in eight states and now to one dairy worker. That part of the story is new.

But that same avian flu has been spreading through wild bird populations for years, and it’s led many farmers to depopulate their poultry stock in hopes of containing the outbreak with limited success. Here to talk about this devastating bird virus, why the jump from birds to mammals is making virologists anxious, and how worried the rest of us should be is Dr. Nichola Hill, Assistant Professor of Biology at the University of Massachusetts in Boston.

NICHOLA HILL: Thanks, Maggie. It’s wonderful to be here.

MAGGIE KOERTH: So this particular virus has been circulating for a little while now, correct?

NICHOLA HILL: Yes.

MAGGIE KOERTH: And I want to know a little bit about how it has changed in the last few weeks.

NICHOLA HILL: Right. So agreed that this virus has actually been circulating for the last two decades. And in slow motion, it’s been evolving between poultry and wild birds, but usually contained to certain parts of Eurasia. And in the last handful of years, we’ve seen this virus expand into new geographic locations, including the US, where it’s also shifted further south into South America, and finally, into Antarctica.

So this virus now has a global distribution in wild birds. And during the last two weeks, what we saw was a consequence of this virus being really widespread in wild birds, where it managed to jump from wild birds in a farm setting to dairy cows, and finally, into humans. So this is a great demonstration of how well this virus is able to jump between hosts that are completely unrelated very efficiently.

MAGGIE KOERTH: So when I went to a Halloween party in 2006, and a virologist friend was dressed as H5N1, that’s the same virus. It’s not a different version of that.

NICHOLA HILL: That is the same one, yes. That is absolutely the same one. It’s been what I would call simmering away for a good couple of decades now in certain parts of the globe. But it’s just expanded, and it’s increased its host range at the same time. And the consequence has been these really unpredictable host jump events that are now happening with a frequency and that many of us in the flu community just didn’t see coming.

MAGGIE KOERTH: So there are these big biological differences between wild bird shows up dead on a farm and a cow, and then now you’ve got one person who worked on the cow farm contracting it. Tell me a little bit about some of the risks there when you have a virus jumping between these very different organisms.

NICHOLA HILL: Right. So this is a unique combination of hosts and the virus. We didn’t anticipate this happening, where H5N1 could possibly jump from wild birds into cows. That’s completely original. It does speak to how well this virus is able to jump into hosts that are completely unrelated. And I think that is something that has caused alarm.

So I should clarify that we didn’t actually see any of these mutations that would signal adaptation to mammals in the cattle. But what we saw was adaptations in the human. There was one very clear marker of mammalian adaptation, and that is usually the entry level for the virus to start fine-tuning its genome and become better-equipped to replicate inside a mammalian cell.

But the fact that it’s gained that single mutation is, again, making us pretty uncomfortable about the possibility of this happening again. And so the chances of this happening again in another host are actually pretty high.

MAGGIE KOERTH: Well, so what’s happening to this one person? What kind of symptoms did they end up developing?

NICHOLA HILL: Very mild. So there was reports of red eye or conjunctivitis. So they were able to recover with only showing mild symptoms. And that’s good news for human health.

But it’s also a bit of a mixed blessing because we know, when the virus tends to show or present as a mild respiratory infection, it can also spread more easily, and that makes it more difficult to detect with surveillance. So this is sort of a mixed blessing and one we will have to step up monitoring of a lot of our agricultural workers to make sure that these host jumps aren’t happening unseen or undetected.

MAGGIE KOERTH: OK, so this is obviously not the first time we’ve seen this kind of situation where a flu virus that’s common in animals makes a jump to a handful of people. It’s not even the first time with this particular virus, but it feels a little bit different now– I mean, to me, anyway– because of the experiences we’ve all had over the last few years.

So help us understand a little bit about this. What usually happens in a situation where you get a spillover to one person, and it’s a mild case? And also help us understand how worried you are now personally about the possibility of new pandemics.

NICHOLA HILL: Right. It’s always on the mind of every scientist everywhere, I think, to monitor and be really aware of the evolution of influenza viruses. They’re amazing at adapting to new host types that are completely unrelated. We have seen this before. As you were saying, there have been over 800 cases of H5 spilling over from an animal into humans over the last handful of decades, and typically it dead-ends in that human host.

And that’s the moment that we all breathe a sigh of relief. And it doesn’t seem to be capable of efficient human-to-human transmission. And that’s the part where we’re a little bit upstream of that event by, I would say, a good handful of mutations. And we’re tracking that evolution of the virus to see how close it gets.

And at the moment, it’s shown a single mutation in humans of mammalian adaptation, but it does need a handful of others across multiple different genes to finally unlock efficient human-to-human transmission so that the possibility of the virus transmitting, say, via a sneeze or a cough. And that is the sweet spot for the virus to start to become efficiently spread from human to humans.

MAGGIE KOERTH: So right now, it’s kind of a carefully watching this–

NICHOLA HILL: Yes.

MAGGIE KOERTH: –keeping an eye on what’s going on. And I want to also talk a little bit about what the farmers have been doing, because this has been spreading in poultry in the US for a couple of years now, and farms have been trying to limit the spread by what’s called depopulation. Can you explain what that process entails and why, with this jump to cows, you don’t think it’s the best course of action to take?

NICHOLA HILL: Yeah. So the current guidance on how to respond to an outbreak in poultry is culling or depopulation. And so flocks that are infected need to be destroyed immediately, and that limits the possibility of transmission between barns or between poultry. And that has been really common as a policy that’s been applied for the last two decades, I would say.

But I think we’re experiencing that this might be unsustainable as a practice because it brings into question ethics around animal welfare, as well as the consequences for the cost of agriculture. This is agriculture that we rely on in terms of chickens and dairy cows that are consumed daily. And so these have huge economic consequences, as well as consequences for animal welfare.

And I think this transmission into cattle brings into focus that depopulation isn’t always the solution. And the current advice is, actually, just quarantine and supportive care and making sure that we’re just doing intensive monitoring of our cattle, and poultry, and other livestock populations to make sure that we’re aware of the virus early enough so we can actually act without actually needing to depopulate these stocks.

MAGGIE KOERTH: I’m curious also a little bit about the broader implications for agriculture here because you talked about things that need to change around the way that we handle avian flu once it’s there. But there’s also the spread of flu, the spread of viruses from animals to people. There’s a lot of connections between that and these problematic agricultural practices, in general. So what needs to be changed there in that bigger picture to really help prevent the spread of viruses between animals, and particularly poultry, and the people who are taking care of them?

NICHOLA HILL: Yeah, this is a great question. So industrialization of agriculture has been born out of necessity for food security. We need to feed a growing population. But I think we’re discovering the flip side of that now, where there’s no putting this virus back in the box. H5N1 is now globally distributed. And we have to think about ways beyond depopulation to rein in and control this virus. And it’s going to take some creative thinking.

And there’s been discussions in other parts of the globe about scaling back agriculture to medium or small-scale farming, as well as vaccination, and even considering more Indigenous breeds of animals that might actually be naturally resistant to disease rather than the current stocks, which tend to be quite genetically identical and, therefore, don’t have a lot of resistance to a novel pathogen like this when it enters into a barn, say.

And so I think there’s a lot of big thinking about how we need to approach this question because it’s now this combination of factors that’s at play now. We have animals that are dying in the millions, both wild and domestic animals. We have the possibility of a large pandemic potential as a consequence of this virus moving around the landscape.

These practices are largely inhumane for how to depopulate these flocks in response to bird flu. And so I think there’s many reasons to motivate us to really think creatively about how to stop this virus from spreading. And it probably isn’t going to be one solution alone, but a combination that gets us there to a place, this happy medium between having enough food for a growing population and making sure that we are prioritizing animal health and welfare, as well as stopping the next possible pandemic.

MAGGIE KOERTH: Thank you so much for taking the time to talk with us about this.

NICHOLA HILL: Absolutely. My pleasure.

MAGGIE KOERTH: Dr. Nichola Hill is an assistant professor of biology at the University of Massachusetts in Boston.

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