Science Friday - Baltimore Bridge Collapse | Mapping How Viruses Jump Between Species

Episode Date: March 29, 2024

We look into the engineering reasons why the Francis Scott Key bridge collapsed after a ship crashed into it. Also, a new analysis finds that more viruses spread from humans to animals than from animals to humans.The Engineering Behind Why The Bridge In Baltimore CollapsedOn Tuesday, a large section of Baltimore’s Francis Scott Key bridge collapsed after an enormous container ship lost power and collided with the structure. Two people were rescued from the water, two bodies were recovered, and four others are unaccounted for and presumed dead.The structural failure of the bridge, which cut off a key roadway and a major international shipping port, has many wondering why this happened. Does the fault lie in aging infrastructure or in the manner the container ship struck one of the bridge’s main supports?Guest host Arielle Duhaime-Ross talks to journalist Swapna Krishna about the engineering reasons behind why the bridge collapsed and other top stories in science this week, including rockets NASA is launching during next week’s solar eclipse, new research about how Homo sapiens traveled out of Africa, and visualizing the magnetic field of the black hole at the center of our galaxy.Mapping Out How Viruses Jump Between SpeciesIn the world of emerging infectious diseases, one of the looming threats comes from the so-called zoonotic diseases—pathogens that somehow make the jump from an animal host to a human one. This includes pathogens such as COVID-19 and avian influenza, a.k.a. bird flu, which can sometimes cross the species divide. But a new analysis published in the journal Nature Ecology and Evolution finds that when it comes to viruses, more viral species appear to have jumped from humans to animals than the other way around. And even more cases of interspecies transmission don’t involve humans at all.Cedric Tan, a PhD student in the University College London Genetics Institute and Francis Crick Institute, joins guest host Arielle Duhaime-Ross to talk about the analysis, and what it tells us about our place in a global web of viruses.Transcripts for each segment will be available after the show airs on sciencefriday.com.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

What kind of viruses could we be passing on to animals? We have to improve our capabilities to predict the next emerging infectious disease. It's Friday, March 29th, and you're listening to Science Friday. I'm Cyfry producer D. Peter Schmidt. When we talk about emerging diseases, one of the looming threats is the so-called zoonotic disease, pathogens that somehow make the jump from an animal host to a human one, think COVID-19 or bird flu, which sometimes crosses the species divide. But new research finds that when it comes to viruses,

more of them appear to have jumped from humans to animals instead of the other way around. So how can scientists better predict these future outbreaks? But first, guest host Ariel Duom Ross talks with space journalist Swapna Krishna about the top news and science this week. A large section of Baltimore's Francis Scott Key Bridge collapsed earlier this week after container ship lost power and collided with the structure. The structural failure of the bridge, which cut off a key roadway and a major international shipping port, has many wondering why this happened. Does the fault lie in the initial design, in aging infrastructure, or is it unreasonable to assume that parts of a bridge, or all of it, might survive this kind of collision? Here to talk about the bridges engineering and other science stories this week is Swapna Krishna, a space journalist based in Philadelphia, Pennsylvania.

Welcome to Science Friday. Thank you so much. So tell us what we've learned about the bridge's collapse. Well, this bridge collapse is horrifying. I think it triggers something visceral in a lot of us, a fear of. of a bridge falling while we're driving over it. And there's been a lot of talk about aging infrastructure, which is an important discussion we need to have in the U.S.,

but that's not the issue in this case. It's literally just an absolutely massive ship. It is hard to understand the scale of the Dolly. It is 300 meters long. And for reference, the Eiffel Tower is 300 meters tall. This ship is 95,000 tons. when empty, and it was not empty, moving at nine miles per hour. So literally, it hit one of the two key support structures of the bridge and obliterated one, and the bridge collapsed.

It was not about aging infrastructure because of the bridge's design. Nothing could have avoided this. Okay, so tell me more about the bridge's design. What do we know about that? It was a trust bridge. And that means the interconnectedness of its design is what kept it stable. But the weak points were these two concrete piers. And as early as 1980, experts flagged that a direct hit from a heavily loaded container ship would bring down the bridge.

So they have known about this problem for a while. It's not a design flaw necessarily. It's just a weakness. But it is important to note that any bridge can collapse. You cannot build a collapse-proof bridge. But building a bridge like a cable-stayed bridge would reduce that risk, especially in the event of another collision like that. Okay. So I'm super pumped about the solar eclipse. I'm already preparing for it. And I hear that NASA has a plan to launch rockets while it's happening. What's that about? I think this is such a cool story. So yes, NASA will launch sounding rockets into the eclipse to study changes in the ionosphere during the eclipse. And the ionosphere is basically the boundary between Earth's breathable atmosphere and space, about 55 miles to 310 miles above the Earth's surface.

What's a sounding rocket? A sounding rocket. They're basically launched in a parabolic trajectory. They only spend anywhere from five to 20 minutes in space. So they're suborbital flights. These are good options for studying the atmosphere because they can be launched from small rockets that don't require expensive boosters. Okay. And what does NASA hope to learn from these launches?

So basically, our ionosphere is always changing. And this area is electrified because what the sun does, is it heats up gases in the upper atmosphere. And then they lose electrons. And then the sunsets, the ionosphere thins out because these ionized particles recombine and regain their electrons and neutralize their charges. And then the cycle starts again when daylight hits. And it's important to note that things like solar storms and space weather also affect and change the ionosphere. So the idea is studying these changes, especially the sudden changes that will come with the eclipse, because it's going to have a similar effect as night falling, but it's going to happen all of a sudden.

Okay, so this is just, it's like a sped up version of it where they get to test a slightly different, slightly different conditions. Exactly. And what's key about the ionosphere is it's important for radio communication because radio signals bounce off the ionosphere. So whenever we have an event like this or a solar storm, radio communication gets disrupted. So part of this is studying how we can minimize these disruptions. Hmm. All right. All right. I'm interested in that. Staying in space for a bit, NASA's considering ending operations on one of its satellite observatories? Yeah, this is kind of a sad story. NASA is dealing with budget cuts, and so the fiscal year 2025 budget had some alarming news. They're basically stepping down operations of the Chandra X-ray telescope, which was launched in 1999.

Chandra is currently the only high-resolution X-ray telescope in the world. So this would affect global science. And the telescope still doing great science is the thing. If it's shut down, there is no replacement anytime soon for at least a decade. And Chandler studies things like dark batter, the structure of black holes, stellar explosions like supernova, it's really important to science. All right. So we'll be keeping an eye on that. Coming back down to Earth, it looks like there's bird flu going around on some farms. It's affecting dairy cows in the south of the U.S. What's going on with that and how worried should should people be? So yeah, this is kind of the rare bird flu story that doesn't end in horror. People are probably really familiar with bird flu leading to mass slaughter of poultry.

But in this case, it's not terrible news. So yes, the milk from dairy cows in Texas and Kansas tested positive for bird flu. The strain is type H5N1, and that can sometimes affect people, and that can be a concern. But it's good news that the specific mutation in these cows does not look like it will easily transfer to humans. So that's one piece of good news. The other piece of good news is there is no slaughter required. These cows are getting the equivalent of basically a cold. All this is doing to them is decreasing milk production and lowering appetite. And they recover in seven to ten days on their own. So that's very good news for the farmers and the cows as well. And there's new research that's giving us more clarity on how and where homo sapiens lived after

leaving Africa tens of thousands of years ago. Tell me about that. Yeah, this is super interesting. So just to paint the bigger picture, our species homo sapiens emerged 300,000 years ago in Africa. And then 60,000 to 70,000 years ago, they migrated to other parts of the world. But there's kind of been a lingering question of where they went after they left Africa, but before they moved on to Europe and Asia around 45,000 years ago. So now we have a paper in nature that identifies where that hub was located in what's now, Iran, Kuwait, parts of Saudi Arabia, and the UAE. So basically to do this, they use genetic data to kind of figure out a larger area that homo sapiens could have settled in between these migrations and then use paleo-ecological data to figure out

what would be the most attractive spot for these ancestors. Okay, so the big news there is that this study showed that. that basically instead of moving around for a while after leaving Africa, homo sapiens stayed in this one major spot for a period, right? That's the big deal there. Yeah, they stayed in one spot, and they lived in small bands of hunter-gatherers, and because there was a diversity of environments and ample resources in this area, that would have been attractive to them.

And this next story is both fascinating and entirely depressing, but in the nerdiest way, it looks like we're seeing another unexpected effect from climate change. It's affecting how we keep track of time. Yeah, so as a space journal, and sometimes it's easy to forget that space science and, you know, kind of climate change are very connected, and this latest study really emphasizes that. It's a paper in nature, and it's showing that the melting of our polar ice caps is speeding up the Earth's rotation. Okay, and what is the implication for time? Basically, right now, we use the leap second to keep our clocks in sync with astronomical time, is the precise rotation of the Earth. It's important for a lot of reasons, including for things

like GPS, that need to know precisely where and when you are to tell you where you need to go. And in the 1970s, we discovered that the Earth was actually slowing down its rotation because of tidal friction. And you can think of that as like tides, except all over the world. And to keep our time in line with astronomical time, they added the leap second, which is one extra second at the end of the year. There were 27 leap seconds added between 1972 and 2016. But now the Earth is speeding up. That's happening for two reasons. First, meltwater from the poles is making its way to the equator. And so that's shifting the Earth's mass. And there's more of an equatorial bulge than there was before. And then in addition to that, land that doesn't have ice on it anymore, sourcing Greenland and Antarctica mainly, that's rising. And that's

making the Earth more spherical. So these two things are actually contributing to the Earth's rotation speeding up. Wow, that's really interesting. Okay, so if we were previously adding seconds because we were slower and now we're speeding up, what's the solution to that? The pay preposites, we might have to start subtracting leap seconds from the calendar, but these things can be very hard to predict, so we'll just kind of have to see what happens. This is so cool and so weird and also so sad that it's because of climate change. But yeah, definitely some good nerdy stuff. So another cool thing for the first time scientists visualized the magnetic field of a black hole.

What does that mean? How did they do it? Yeah, this is really, really cool. So if you haven't seen the picture, it's basically this orange photo of kind of a fuzzy black hole with these lines around it. and you can see kind of the direction of movement through those lines. So this is a photo of the black hole at the center of our galaxy called Sagittarius A-Star. It's not a direct image of the black hole because you can't directly observe a black hole, but you can see the event horizon and the bright accretion disk.

Now, these lines are magnetic fields spiraling around the black hole, but it's important to note they aren't really there as in this is not a direct photo. but scientists observed Sagittarius A-Star in polarized light and added these field lines over an image from the event horizon telescope. So basically, we're looking at the movement of the magnetic field around the black hole at the center of our galaxy, and polarized light is specifically important here, because light waves can be oriented in any direction,

and when they are, that's unpolarized light. So polarized light is when the lightways are oriented in a specific direction. And so scientists used this polarized light to study Sagittarius A star's magnetic field because it controls the direction the light waves move. And that allowed researchers to measure the structure, strength, and direction of the magnetic field. And this movement contributes to the emission of jets of matter from the accretion disk of the black hole. And so this tells us that our supermassive black hole may have jets that we don't know about yet. Whoa. Okay. Thank you.

so much for bringing us these stories, Swapna. It was a pleasure having you on the show. Thank you. That's Swapna Krishna, a journalist based in Philadelphia, Pennsylvania. This is Science Friday. I'm Ariel Dermross, sitting in for Irafledo. When we talk about emerging diseases, one of the looming threats is the so-called zoonotic disease, pathogens that somehow make the jump from an animal host to a human one. Think COVID-19 or Asian. avian influenza, aka bird flu, which sometimes crosses the species divide. But a new analysis published in the journal Nature Ecology and Evolution finds that when it comes to viruses, more of them appear to have jumped from humans to animals instead of the other way

around. Joining me now to talk about that finding is Cedric Tan. He's a PhD student in the University College London Genetics Institute and Francis Crick Institute. And he's the lead author on that report I just mentioned. Welcome to Science Friday. Well, thanks, Ariel, for having me. Yeah, great to have you. Okay, so to start out, how do you track the path of a virus from one species to another? Right. So to do this, we use statistical methods based on the genomic sequences of the virus. And what we can do is using these methods, we can try to reconstruct where the virus has come from, say if it has infected birds at some point and then was passed on into, say, humans. And this is what we call ancestral reconstruction. And so using these tree of lives generated

from viral phylogenies, we can try to infer the direction of flow of viruses. So what I'm getting from you is you can look at the viral genome of a virus that infects humans and then also the genome of a virus that infects pigs or bats and go these genomes are very similar. It's the same virus. And by looking at the different changes, you can sort of reconstruct what happened and how those jumps occurred. Yes, we know what is an ancestor virus and what we know what is a descendant virus. And based on this, we can say, okay, the ancestor has been found in pigs, for example, and the descendant has been found in humans, for example.

And so based on that, we can say that this virus has actually jumped from pigs into humans. Okay, so in this project, you were looking at thousands of viral genomes. How many did you study? There are two different analysis presented in this paper. So the first one was to kind of assess the state of genomic surveillance around the world. And so basically what we have collected so far, what we have sequenced so far. And so for this analysis, we used about 12 million viral sequences, and this was uploaded by various labs around the world to a public database called NCBI virus. And then we further subsampled this set of viral sequences to around 60,000 sequences.

So these are 60,000 high-quality complete viral genomes. And these were used for our detailed analysis of viral host jumps. And so this library of viral genomes, how does that compare? to the whole universe of viruses out there, right? How big is this library? Yeah, this is an excellent question. And the short answer is we don't really know because we've largely focused on the viruses that infect humans. So we don't really know the true number of viruses that infect animals beyond humans. So in fact, only 9% of fish families are represented in the database and 13% of amphibians were represented. We are still discovering new

viruses every day. So the estimate of the true viral diversity that we expect keeps changing as we discover them. Did certain types of viruses seem more likely to cross to another host than others? Yes. So one of the other messages in our paper is that viruses that can already infect a broad range of hosts are more at risk of jumping into a new host. In fact, we've known that many viruses that have recently jumped into humans have remarkably broad host ranges. One example of this is SARS-Cobie 2, which caused the COVID-19 pandemic. And this virus can infect nearly every mammalian order while requiring minimal adaptations. So what we found in this study is really that, you know, these broad host-range viruses are what we should be focusing on to potentially identify the next

pandemic virus because they are more likely to jump into a new host species. When you say more likely to jump, what does that actually mean? Like, what does a virus need to have? What characteristics does it need to have to be able to make a cross-species shift? Is there like a special recipe, a magic sauce? Well, it's not really a magic source. But first of all, a virus in an infected host must first be able to transmit the virus, either via infected fluids or being excreted through feces or through various other modes of transmission.

And then the virus must then be able to enter the cells of the new host. And the virus must also then be able to survive and replicate in a new host cell. So these are some of the kind of barriers to entry when the virus is trying to exploit a new host species. One other thing is that most viruses don't really have their own replication machinery. And so they must hijack the proteins in the new host cell to be able to. to replicate themselves. And after replication, the virus must then be able to transmit from the new host to other

hosts of the same species sufficiently well so that they can circulate in this new host population. You estimate the number of shifts, animal to human, human to animal, and animal animal jumps. What's the magnitude of those kinds of shifts? Right. So in our study, we inferred about 2,900 host jumps in total. 79% of these jumps involves only animals, and only 21% involves humans. So that's about 600 host jumps. Of these 600 host jumps that involve humans, 64% for human to animal,

and half of that, which is 36%, involve animal-to-human transmission events. What does this all tell you? What are the big take-home messages? First thing is that we have a very huge impact on the environment about us. Second thing is that we can start to think of leveraging the huge amounts of genomic data that have been kind of deposited on public databases so far to try to understand the wider flow of viruses around the globe and between different animals. And I think that's really important because we've been focusing on zoonosis,

we've been focusing on things that affect us. But we are just a single species in this really broad and diverse. network of hosts around the world. And we have to stop being so myopic and try to understand this wider ecological network to better understand and improve our capabilities to predict the next emerging infectious disease. Sedric Tan is a PhD student in the University College London Genetics Institute and Francis Crick Institute. Sedrick, thank you so much for talking with me today. Well, thank you, Ariel. It was a very nice chair. And that's it for today. Lots of folks help make the show happen, including

Nehima Ahmed. Emma Gomez. Annie Niro. George Harper. Next time, we'll dive into the mind-bending physics behind Netflix's adaptation of the three-body problem. But for now, I'm SciFri producer D. Peter Schmidt. See you then.