transcript

Speaker 1:
[00:01] Have you ever wondered what's the best glass shape to drink beer out of? And why do elevators always seem to be going in the opposite direction when you need them the most? And how are you supposed to cut pizza fairly if the toppings are all in different places? These questions and many more can be answered with math. Hi, I'm Andrea Garleski, and I'm in charge of all newsletters here at Scientific American. We have a new weekly newsletter called Proof Positive. It's about the math that can help you answer questions like these and many other mysteries of life. Plus, it rounds up the latest math news and has a puzzle to challenge your mind. Go to scientificamerican.com/newsletters to sign up.

Speaker 2:
[00:54] For Scientific American, Science Quickly, I'm Rachel Feltman. What comes to mind when you think about wildlife trade and diseases like COVID-19? If you live in the US., you probably picture so-called wet markets in Asia, where people buy and sell animal meat in an open-air setting, or perhaps foreign-sounding bush meat. But in reality, the wildlife trade is everywhere, including at your local suburban shopping center. And new research suggests that pathogens are spreading through this global trade network far faster than anyone realized. Here to tell us more about these findings and their implications for the spread of zoonotic disease is Colin Carlson, an Assistant Professor of Epidemiology at Yale University School of Public Health. Thanks so much for coming on to chat today.

Speaker 3:
[01:48] Thanks for having me.

Speaker 2:
[01:50] To ask a very basic question, why is it that contact with animals leads to new diseases emerging?

Speaker 3:
[01:58] Pathogens have to have an opportunity to get to us, and that usually means proximity. We have to be close to another species. We are close to animals in our day to day life all the time, much more than we think we are, right? We have our pets in our house. Maybe we have that pigeon that sits on the window outside of our office. But we also have rats living in our buildings. We have bats roosting in our attics. I'm from Connecticut, so we had flying squirrels living in our attic when I was growing up. Who knows what viruses those guys have, right? We are constantly in contact with wildlife, but most of the time, it is very indirect and it's very rare. Wildlife trade changes that equation. You are talking about people handling animals, butchering animals. You're talking about moving animals thousands of miles sometimes, and that means that people are shipping them. They're storing them in these dense conditions where the animals usually get pretty sick. And in all of that, what we're also doing is we're putting animals together in combinations that don't necessarily exist in nature. And that means that viruses and other pathogens are spreading not just from animals to people, but between animals back and forth. We're sort of turbocharging their evolution, right? We're giving them all of these different opportunities to just bounce between hosts until they get something right. All of that makes it much easier for a pathogen to get into humans in the long run.

Speaker 2:
[03:21] So you recently published a study about the wildlife trade and zoonotic disease. Can you tell me a little bit about how you and your co-authors came to be curious about that question?

Speaker 3:
[03:32] Sure. We have been worried about the wildlife trade and public health for a long time. COVID comes to mind, obviously, with sort of this question of where did SARS-CoV-2 come from? But we've been thinking about the wildlife trade for much longer than that. You know, SARS started in the wildlife trade. We hit an outbreak of M pox in the United States back in 2003. And, of course, HIV probably started with rural hunting communities in Africa. And so there's always been this understanding that wildlife trade is probably a risk to human health. But what's been really hard is we don't know how to quantify that, right? We have a lot of anecdotal evidence. We have these individual outbreaks that matter a lot to us. But we haven't had a big picture look at what is the cumulative impact on our health. So that's sort of the jumping off point for this.

Speaker 2:
[04:19] And where did you go looking for that data?

Speaker 3:
[04:21] So we're doing a very like global look here, right? So we're saying, okay, here's every species that we know exists in the wildlife trade. And here is every virus that we know those species have. And we're putting those data together and we're saying, what does that tell us about how viruses are moving around? Those data are incredibly hard to get on both sides, it turns out. We don't know a lot about the wildlife trade and we know even less about what viruses most animals have. So it's taken a long time to get enough data to ask a question like this. But we're finally at this point where we know enough about some of these species that we can say, okay, here are the viruses that are in animals. And then as they spend time in the wildlife trade, here are the viruses that are making the jump to humans. And that's the red flag we're looking for.

Speaker 2:
[05:09] Yeah. Well, one thing that I thought was interesting, the fact that I think it has something like a quarter of vertebrates are traded in some way. And I think most of our listeners will probably hear what this study is about and think like, oh yeah, bats. But can you tell me a little bit more about just how broad this issue is, what kinds of animals are we talking about, what kinds of diseases?

Speaker 3:
[05:32] Wildlife trade is everywhere, right? I think we have this idea in our head of sort of this wet market with exotic animals and it feels very foreign to us. But anytime you go to PetSmart and there are geckos there, there are tetras that come from the Amazon rainforest, right? All of those species are, that's wildlife trade. We do wildlife trade in our day-to-day lives. If you've ever worked at a PetSmart, if you have watched the Joe Exotic documentary, right? All of those tigers, that's wildlife trade. And maybe we don't all have tigers, but I guess more of us do than we thought, right? But I think that idea that like a quarter of species are in the wildlife trade, humans just interact with wildlife constantly, right? We eat them, we turn them into products, we keep them as pets. There are so many different ways that we are interacting with animals and there's sort of no limit to how many species get pulled.

Speaker 2:
[06:29] Yeah, so what other misconceptions do you think the public has about the relationship between wildlife trade and disease?

Speaker 3:
[06:36] I think that there is this common idea that all we have to do is just ban the wildlife trade, right? That this is a simple problem that exists somewhere else when in reality it's a here problem and it's an everyone problem and it's probably not going away. One of the things that I think a lot of people don't know about wildlife trade is at the international scale, it actually looks a lot like climate change or deforestation, where a lot of the impact is falling on biodiversity in tropical countries, in lower resource communities, but it's driven by economic demand from the US and Europe and China. That means that first of all, we have a role to play in reducing demand. It's not just another people problem, it's an us problem, it's an everyone problem. But it also means that we are probably not able to just ban wildlife trade. What happens when we do that is we push trade underground, and this has been seen again and again over the last few decades. Every time we get really worried about wildlife trade, we go and we scramble and we try to shut it down, and it just doesn't work.

Speaker 2:
[07:40] Can you give me a sense of the scope of the data that you guys were working with?

Speaker 3:
[07:44] Sure. So what's really special about this study is that we have more data than we've ever had on animal pathogens. So not just viruses, but also bacteria, fungi, parasites, there are worms that come from animals to humans. And we have more data than we've ever had in one place on wildlife trade. So we're looking over about 40 years of trade. The wildlife trade has changed dramatically in that time. If you think about 100 years ago, we're talking about rural communities living off of wild animal hunting. But wildlife trade has become not just international, but industrialized, right? We have wildlife farms at a scale that we've never had. And that's mink farms in the US and it's fur farms in China, right? All of that is a relatively recent thing on the time scale of humans sharing viruses with animals.

Speaker 2:
[08:37] So let's get into your results. What did you actually find when you looked at this data?

Speaker 3:
[08:42] Turns out that diseases are spreading in the wildlife trade much faster than we thought. Wildlife trade is this incredibly intense process. Diseases are moving very quickly. And so what we found is that just being in the wildlife trade makes it about 50% more likely that an animal hosts a pathogen that poses some risk to human health.

Speaker 2:
[09:03] Wow.

Speaker 3:
[09:04] You know, again, wildlife trade is sort of ubiquitous within mammals, right? So it's actually quite striking we get that strong result. And then the part of the study that I just think is so cool. There's always a possibility, right, that this is just correlation. So if you think about some of the species we trade a lot, there are a lot of primates in the wildlife trade. We also share a lot of pathogens with primates, not because of the wildlife trade, but just because their immune systems look like ours. It's very easy for diseases to move back and forth. That's not necessarily causal, right? So how do we disentangle those things? Well, the trick here is for most of these species, we know how long they've been in the wildlife trade. And that gives us the smoking gun. So for every 10 years that a species is traded, on average about one more pathogen makes the jump. Think about that versus like 10,000 years of livestock disease, right? It's so fast, and we wouldn't see that pattern if there weren't something dramatically different happening in the wildlife trade than in any other setting, really.

Speaker 2:
[10:08] So do you have any thoughts on what we should be doing about this?

Speaker 3:
[10:12] Wildlife trade is a hard problem to solve. I've worked on it for a long time, I have for a long time been one of the sort of dissenting voices on, you know, we shouldn't just be rushing to ban everything. And that's because I don't want to see trade get driven underground. One thing that we find in this study is that black markets actually probably make all of these problems even worse. So species that are illegally traded are actually sharing even more pathogens with us. Criminalizing doesn't seem to work. There's also like human rights issues here, right? We can't just solve everything with criminalization and among other things. You know, think about if we know that the next pandemic is going to start with someone who handles wildlife, someone who works in a market or works in a supply chain. When that person gets sick, we need them to be able to go to the doctor without being afraid that they're going to go to jail. So we can't just ban the wildlife trade. There are a couple of things that we can do, though. One is we can try to reduce demand, particularly in the US. A lot of wildlife trade is our fault. Next time you're at Petco, think about whether you really need that gecko. Another thing that we can do is we can invest in alternative careers, in communities that rely on particularly things like wildlife farms that we really don't need. I think it's going to be very hard to shift people off of wild animal protein. There's actually studies that show that the task of doing that would actually lead to so much more agriculture in some places that it would actually be worse for biodiversity. So some people are always going to be living off of wild animal protein. That's not just in faraway places. There are certain industries, especially fur farming, that we just really don't need. And I think it is very reasonable to think about eliminating them. The last piece of this, though, and to me, what the public health answer is, there's always going to be some wildlife trade. And, like with climate change or biodiversity loss, it's going to take us decades to solve this. We can't wait to solve wildlife trade to be ready for the next pandemic. So, what that means is we need to start looking for viruses in markets, on farms, in the people who work in these settings. We have really poor disease surveillance in most wildlife trade communities. And, statistically, the next person to get a SARS-like virus is probably going to be one of those workers, right? And we want to be able to, day one, when we see that first case of SARS-CoV-3, we want to be there. We want to be ready to quarantine people. And we have to be able to do that transparently and with trust with communities. And all of that is just, it's a huge state shift in how we think about these problems. But I think public health has to tackle it, or we're just gonna keep having more COVIDs.

Speaker 2:
[13:10] As somebody who's working this field and looking at this data, what are some things we need to be doing to prepare for the next pandemic?

Speaker 3:
[13:19] We need a lot more basic science about viruses and animals and the connections between them. There are a lot of just foundational things we take for granted about how ecosystems are changing or how people are affecting disease patterns in nature. And we just don't know for sure. We don't know how many people die from climate change every year. We don't know where wildlife trade is actually accelerating the fastest. There are things we can measure from space. So maybe we have a sense of where deforestation is happening. But for the most part, we don't have eyes and ears in most of the places where the next pandemic will start or the next planetary crisis is happening. So I think just we need so much more basic investment in science and in data collection. There's a lot that we can do with the data that's already out there, but we need a lot more data before we can actually start to tackle some of these problems. I think that this project is a really great poster child for basic science, all the boots on the ground tracking of wildlife trade. But five years ago, we wouldn't have been able to do this study because we didn't have a list of, here are all of the animals and here are all of the viruses they have. Five years ago, we couldn't ask that question with the data we had and five years from now, we might not be able to because the data might not be supported anymore. So a general plea here of we're doing what we can, but I hope that this is a wake up call that we have to keep investing in this kind of work.

Speaker 2:
[14:51] Well, Colin, thanks so much for coming on to talk to us about this study. I really appreciate it. Thank you. That's all for this week on Science Quickly. We'll be back on Monday with our usual Science News Roundup. Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Sushmita Pathak, and Jeff DelViscio. This episode was edited by Alex Sugiura, Shayna Posses, and Aaron Shattuck, Fact Check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news. For Scientific American, this is Rachel Feltman. Have a great weekend.