Daniel and Kelly’s Extraordinary Universe - How did we tackle Trichinella?

Episode Date: January 28, 2025

Daniel and Kelly talk about how public health officials turned "the most serious parasitic disease in New England" into a disease that only afflicts about 15 people per year in the whole of the United States. See omnystudio.com/listener for privacy information.

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to the American Society of Parasitologists. His talk was called This Wormy World. And if you study parasites, this talk is a real classic. Stoll wanted an estimate for how many people in the world were carrying particular kinds of wormy parasites. So we're talking things like nematodes, tapeworms, and trematodes. Not the kind of things that cause the flu, so not bacteria or viruses.

So the context here is that World War II had recently ended, but the problems for U.S. soldiers who participated in the war had not. Soldiers returning home from the war had brought back with them the parasitic diseases that are found all over the world. U.S. interest in parasites skyrocketed as Americans were suddenly forced to observe how horrible some of these parasitic diseases can be. So, how many wormy infections are out there? Well, Stoll starts by noting how bad the data for an analysis like this are. There's just not great surveys that are comprehensive, but he set out to do his best.

What he concludes is that there were 2.2 billion wormy infections in a population of just under 2.2.4.4.4.2 billion wormy infections in a population of just under 2.5. So this isn't counting the number of parasites in people. One infection would be like, okay, you have one of a particular kind of nematote in someone. But these infections were not evenly distributed. On average, one out of every three Americans or Europeans were infected. But in the USSR, that number was up to two out of three people. For every three people in Asia, the Middle East, in South America, there were four infections. So that means out of three people, one of those people is probably harboring two different

wormy parasite species. And every person in Africa, on average, was estimated to harbor two Helmuth parasite species. But stole notes a bit of optimism and points out that six out of the seven cases of wormy infections could have been stopped with proper sanitation. So there's some ability to do something about this. So how far have we come since 1947? Well, in some areas we've made great progress. For example, Stoll mentioned that a nematode called trichinellus paralysis

was known as the most serious parasitic disease in New England. At the time, one in six Americans were infected with this parasite. Now, trichinolosis is a rare disease in the United States with only about 15 confirmed cases in the entire country per year. And today we're going to be talking about this public health success story. But in future episodes, we're also going to talk about some parasites that still plague humans worldwide, including here in the United States. For example, according to the World Health Organization,

one and a half billion people are infected with nematode parasites that are picked up from the soil. All right, so let's dig in. Welcome to Daniel and Kelly's extraordinarily wormy universe. Hi, I'm Daniel. I'm a particle physicist, and I've never been infected by a parasite, to my knowledge. I'm Kelly Weiner-Smith, and I bet Daniel has been infected at some point. And if I had to guess, there'd be a good chance that you would have gotten pinworms from your kids when they were young. Ooh, pinworms. Are those the ones I'm thinking about that make you itchy in a very uncomfortable place?

That's right. I think actually at some point we should have. a whole episode on pinworms because why not but oh no maybe not Daniel it's going to be a long couple years working with me if pinworms give you the eb-gibis it's just that particular itch just really gets me if you know what I mean no no I get it I get it actually the mom nematode sneaks out at night and deposits eggs with like a sticky substance in the spot that you're thinking of because scratching is how the parasite transmits how it gets under fingernails and then ends up in the environment and then ends up getting eaten. So that itch is very purposefully caused by the parasites. I know, and I use that story as a way to dissuade my kids from biting their

fingernails. Oh, good. Because I'm like, you know what you're doing. You know, where you're going to get itchy if you keep doing that? And it works. It works. No, I bet. Yeah, people feel real gross when you tell them about parasites. It's a good way to dissuade people from certain bad behaviors, no doubt. All right. So since we're being personal, what is the grossest parasite you've been infected by? Oh, gosh, that I've been infected by. Well, I guess if my parasite were including viruses and bacteria, I guess anything that makes me puke, but I haven't been infected by anything that gross. But no, I had a antibiotic resistant wound near my ankle once, and that was gross because I just wouldn't go away, and that was kind of scary. And I was super

stressed, which I think was like suppressing my immune system, too. And so it was bad news. What about you? Well, to me, being infected by a little microbe, isn't that gross? It's like, yeah, that's invisible. The bigger it is, the weirder it is, the more gross it is. Like, being infected by something that's, like, actually a worm size, to me is creepy. It's like crawling around inside you. And so, like, imagine being infected by something larger, you know, baseball sized or, like, football size. That would be like, oh, that's nightmare fuel for me. But, yeah, I don't know that I've ever had a worm inside me. But apparently, Kelly thinks that I have. So maybe I am. a wormy. I don't actually know that you have. I'm sure your hygiene is impeccable and that has probably kept you safe. But no, there's some pretty nasty like ascorid worms, which maybe we'll talk about at some point, they are really big. And when you see surgeries where people are like trying to remove many of them from someone's, that even grosses me out. I can't eat pasta for days. Exactly. Well, I appreciate you giving me the benefit of the doubt, although physicists are not exactly famous for their hygiene. You know, that's not like top.

10 ways you become a physicist or things we're famous for. But, you know, I appreciate it. I do try to keep clean. Thank you very much. You're welcome. I was thinking about you as a human being and not really a physicist in particular, you know. That doesn't work in my favor. Yeah. All right, but today we are not talking about Daniel's hygiene. We're talking about humans more generally. Yeah, and we're talking about them because we got a great question from a listener named Patrick. And let's go ahead and listen to that question now. How many parasites are living in all of us? How common are the bad ones?

And where do we pick them up? Oh, man, it sounds to me like Patrick is looking for nightmares. Oh, it sounds to me like Patrick is giving me my Christmas present early by allowing me to talk about parasites. And so, you know, at the intro, I talked about how in 1947 there was this estimate that there's 2.2 billion parasitic infections in a population of under 2.2 billion people. So some people are infected by more than one parasite. And I wasn't actually able to find a comparable estimate for now.

And I think partly that's because the way he grouped parasites together is not really a biologically relevant category that people care about anymore. And so I wasn't able to find a comparable number. But I am going to go through some of the main parasitic infections that have plagued humans in our recent past. But we managed to get rid of. and then some that are still a problem today in the United States and in other parts of the world. But I figured today we would start with a success story. That's good because I was afraid that the message of this episode was going to be like there's parasites everywhere all up in your eyeballs and in your earballs and in your noseballs and everything. Well, you know, especially if you live in the United States and you're lucky enough to be in an area where there's really good sanitation, you probably are pretty.

safe. But, you know, that's not necessarily true in other parts of the world. We're very lucky here. All right. Well, let's dive in because I want to know by the end of this episode, how likely am I to have worms living inside me right now? Well, we're only talking about one worm, and I was interested in figuring out what people know about this worm, because at least in the United States, infections are very uncommon these days. About 15 cases of infection with this parasite are recorded per year for a disease that once infected one out of six Americans. So we've made a lot of progress. Amazing. And so I was wondering, have people heard about this before? So I asked our audience, what is trichinolosis? Right. And if you would like to play on this segment of the podcast

in the future, please don't be shy. We'd love to have your voice. Write to us to questions at danielandkelly.org. So before you hear these answers, think to yourself, do you know what trichinolosis is? Also known as trichinosis. No idea. The osis at the end, it sounds like it could be some kind disease or medical condition. I'm too excited for words. This isn't about cats and uncertainty and quantum mechanics and things I don't understand. This is a worm. It's a parasite.

It grows in pork mainly. I grew up in India and it was a real risk that we'd get this. So we ate pork that was like leather. You could have put it on your feet and worn it as a shoe. A disease associated with a parasitic infection of a roundworm from cysts from muscle from undercooked meat, pork, and other animals as well, I believe. A leaves caused by bacteria, worms, goblins. Trichinilosis is an infection.

Trichinella could be a bacteria or maybe a eukaryotic parasite. I'm not sure. Trichinosis is a human disease caused by a parasitic worm in pork. I think trichinosis is a disease that one can contract from eating undercooked meat. I don't know if it's a parasite. If Kelly's involved, I assume that it must be, though. No idea. Sounds like a bacterium. Trichinosis sounds like the disease that happens to my third chin, and I don't know anything more about it.

I have no idea what trichinosis is. However, taking a stab in the dark, I'm going to say parasite, but only because the email asking the question came from Kelly. If the email asking the question had come from Daniel, I would just took a stab in the dark and said a particle. There we go. Trichinosis involves a trilobite, a tricycle, and tragedy. So, Daniel, it is so clear to me that our audience has us totally figured out. It is about a parasitic worm.

And, you know, just because the email doesn't come from me, doesn't mean it wasn't particles. I mean, I assume these parasites are made of particles. articles. They're not like fundamental parasites in the universe or anything. These aren't string theory parasites, are they? Not post-quantum gravity parasites. Nothing like that. These are actual parasites. And I am always so amused by the wonderful answers you all give when you don't know the answer. Like, probably it's goblins. And that was great. All right. So give us the context. Take us back in history. When did we first learn about this

particular worm? Well, the first documented case where someone figured out that this worm was causing an infection was from 1835. So we're in London at St. Bartholomew's Hospital. Back then, the way that a bunch of the medical students learned about infections was that an autopsy or a surgery would be happening in the middle of essentially what looks like a theater. Like, imagine you're sitting down to watch a play, but instead you're watching an autopsy.

The first five rows may be splashed. Yes. Yeah. And this was back before there was anesthesia. So like amputations were, oh, gruesome. Turns my stomach thinking about it. But it was an autopsy, and it was a man who had died of tuberculosis. And the surgeons in the middle of the operating theater, they had their scalples, and they were trying to, like, get through the body.

And the scalples kept dulling, and they were feeling really frustrated. And when they finally got inside, they got to the diaphragm. And one of the surgeons said, I knew it. A case of Sandy Diaphram. Sandy Diaphram. Sandy Diaphram. And so one of the guys who was in the audience, his name was John Padgett. he was a medical student and he said what causes sandy diaphragm and this is the thing that was dulling their scalples and the surgeons were like we don't know let's go to life well what was the general state of medical knowledge like was the inside of the human body a total mystery and we mostly figured out like the circulatory system and the digestive system and all that what did we sort of know about the workings of the human body almost 200 years ago i think that if you went to a surgeon there was like a 50-50 chance the surgeon made things worse

I'm not a medical historian, so maybe the odds were better or worse. I don't really know. We knew a fair bit, you know, like we knew that if someone had a cancerous growth, you'd try to cut it off real fast, but we didn't have anesthesia. So sometimes you'd get an infection and you'd die from that. It was a dicey time to be someone who needed the help of a professional. And this is before germ theory, right? So we didn't understand there could be microscopic organisms infecting,

or was this after germ theory? Loua and Hook had been able to see his little animacules. So we knew that there were like tiny little organisms in the world. I don't think we had germ theory and Lister hadn't figured out ways to establish antiseptic technique. That is all off the top of my head. And maybe we should have like Lindsay Fitzherris, who's this amazing historian of like surgeries and stuff on the show to give some background there. Because I thought that like middle of this century, we still have folks like going from cadavers to delivering babies and wondering like, hey, why are so many women dying in childbirth? What a mystery.

Maybe we should wash our hands. Yeah, no, that is where we were. Yeah, okay. We're still before the germ theory. Okay. Yeah, yeah. And I think that, you know, if they amputated someone's limb, they'd kind of like wipe it off with a napkin maybe and then amputate the next person's limb. There were lots of microbes being shared between people at this time.

All right. But sandy diaphragm is not due to microbes, right? It's due to actual visible worms. It's due to actual visible worms. They are not easy to see. So what Padgett did was he took a sample and he used a hand lens and he squished it between two glass slides. And he looked at it with a hand lens and he thought he saw something kind of wormy. But he wanted to get a better look at it.

So he brought it over to the British Museum of Natural History. And he actually knocked on the door of the guy who came up with Brownie and the idea behind Brownian motion. So he knocked on Brown's door. and he had a microscope. He let Padgett use it. And Padgett noted that there was actually a worm in there. Some of the worms were moving and some were not. And the ones that were not had been calcified by the human body.

And that's what was causing the sandy diaphragm. So when these worms die, the immune system responds by sort of like creating like a calcified casket to like wall it off from everything else. And over time, that creates like hard structures. And that is what the scalples were. dulling on. So he goes and he tells a group of medical students about his finding, but he doesn't take the important next step of publishing and sharing his results more widely. The same cadaver, a sample of it got sent to this other guy named Richard Owen, and we don't need to get into too much detail here, but he also, from the same cadaver, ended up looking and seeing these worms.

He wrote it up, he gave a public lecture. He's the one who got the credit, but this one cadaver produced two different people who were the first to notice that actually there were these little tiny worms. And so it used to be called Trichina, I think, which is a word for like tiny hair and Spiralis is, you know, like the spiral shape. And so these are hair shaped worms that curl up in a spiral inside of cells like diaphragm cells. But Trichina also was a genus of flies. And so they went with Trichinella to avoid confusion. So hair like spirally things. And take us back also scientifically. Like if you find worms in a body at that point,

do you have to assume that somehow the people have eaten them or they've invaded the body? Or are we still in a place where like we don't understand whether life can be generated spontaneously? So we in Hook and Pasteur. I think they had already done their experiments at this point where you know that there's little things and you know that those little things aren't generated spontaneously

because Pasteur, and I think, some other people as well, had done those experiments where they had made those flasks that had the like bendy mouth parts so that the air couldn't sort of get in. And whenever air can't get in and you had like a nutrient broth, nothing would grow in it. But if air could get in, you would get growth. And so it's not arising spontaneously. You have to have something seeding the living things. I'm sure that people had seen parasitic worms before, but I don't think we had a very good handle on life cycles. All right. What exactly was new and novel about this? What did this tell us about parasites and humans and all that kind of stuff? So I don't think that this is the first parasitic

disease that was ever discovered. But I think this is a problem that was attributed to a parasitic disease at this point. So like this person in particular had died of tuberculosis. I think it was a while before we realized that this was something that could kill people as opposed to just something that's a pain in the rear end when you're trying to run a scalpel through a dead person's body. But even today, if you get infected by too many of these all at once, you can die. So let's talk a little bit more about what they actually discovered when we get back from the break. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed.

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Okay, so what they had discovered was Trichinella Sparales. This is a nematode, so they've got like a hard cuticle. They kind of look like earthworms, but without the segments. And the ones that we're talking about, the ones that cause trichinalosis, they're very tiny. So they're much smaller than normal earthworms. Do you feel like you've got that image in your head? I'm imagining something that looks basically like a human hair and it's curled up. Yeah.

And if you zoom in on it, it looks sort of like a worm. Yeah, it comes to points at either end, but yes, kind of like a human hair except points at the ends. And so what happens is if you eat meat that's infected by this parasite and that meat's not cooked through all the way, the parasites burst out of the cells that they've been living in. So as your body is digesting the food, it also digest the cells they've been living in and that releases them. So they've been living inside the cells?

Like I'm eating pork. Then these worms are inside the cells of the pig, not swimming around between the cells. Yeah. And this is not something that's super common for wormy parasites to do, but this is something that this particular species does. They live inside the cells. And they can live inside the cells for like 30 years, like incredible amounts of time. So they're smaller than like a pig cell. And they get into the pig cell. They expand the size of that cell. We'll get there. I'm so sorry about the next few years of your life, Daniel. And so they burst out of the cells. They find mates. They produce live smaller worms. And the smaller worms get into your bloodstream or the circulation for your lymph. And then they end up all over your body. But they can only move in and live into skeletal muscle cells. And so when they end up in like your heart or your brain, they try burrowing into those cells.

And then they're like, oh, this isn't home. And they burrow back out again. Because we have two different kinds of muscle cells, right? Smooth and skeletal. Is that right? Three types. Cardiac. skeletal and smooth.

Oh, all right, cool. So why can they only live in one particular kind of muscle? Is it the shape of the cell, the size of the cell, the kind of food they get inside, or? I don't think we know the answer to that, but they do end up manipulating these cells. They are born about a week after you eat the infected meat, and they're going on this journey. And so about a week after you eat the infected meat, this is when you're at the highest risk of dying. Because if you ate a lot of parasites in that meat, they're all having babies, they're all releasing babies. those babies are like maybe if they end up in your brain destroying a bunch of brain cells

or destroying a bunch of cardiac cells. And at this point, you're often given medication to reduce inflammation because that's a big part of what is causing trouble here, the inflammation as a result of the parasites moving around. And sometimes you're given anti-parasite medication. But this is the most dangerous phase of the process. And in order to be at risk of dying, you must need to have lots and lots of these parasites. Can one worm or two worms generate like an avalanche of these things or do you need to eat a lot of the meats you have like a big initial population? Yeah, the more that you eat initially, the worst shape you're going to be in. So if you just happen to eat one or two cells that have the parasite, you're probably going to be

fine. You're still going to have parasites inside you. You're just not going to die. That's what you call it fine. I mean, for most of our evolutionary history, that would have been lucky, just one or two parasites in you. But yes, it won't be a dire situation, I guess. But so when these parasites do find the cells they're looking for, the skeletal muscles, they burrow in, and now this is when they start manipulating the cell. So they call the cell a nurse cell. They like secrete some stuff that gets rid of the parts of the cell that they don't need. They start growing and expanding. The cell starts getting bigger. And then around the cell, I think it doesn't recruit the kind of vessels that bring oxygenated blood because inside the cell you end up with an anaerobic environment.

I don't know why that's necessary. But so they start bringing the kinds of cells. that take deoxygenated blood away. But in this way, the nurse cell delivers nutrients and removes waste. And so the parasites are able to manipulate the cells to become nice homes and to do things like remove waste and feed them. So we don't really understand how this happens, but it does. And Dixon de Pommier wrote this book called Parasites People in Plow Shares, where he argues that if we could understand how nurse cells work,

we could maybe understand, like, better ways of like delivering insulin and stuff like that. And so he's really interested in trying to like physiologically understand what's happening here, but it's a complicated system. So they really have taken over the cell and refashioned it for their own use. It's no longer doing the original thing you had that cell for. It's now basically just like a homestead for these worms. Yep.

It's kind of amazing, I think, that they've managed to like, you know, evolve to do this. I think it's super amazing when they manipulate their environment to respond in a certain way to take advantage of it. Obviously, you know, this is just evolution, right? There's no, like, intentional design here. They're not, like, engineers where they're thinking about what to do, but they found this strategy. Why haven't humans responded in an evolutionary sort of way to create new defenses?

Like, obviously, this is bad if it kills you, or even if it doesn't kill you, it must be bad for you because it's sapping your energy. Do humans have defenses against this, or are we just, like, total suckers for these worms? Well, so some of the worms die, and the ones that die, they get calcified. And I think probably some of them are dying because. of an appropriate immune response. I'm glad to hear something's happening in the inside to push back on these guys. We're doing something.

But, you know, so for a lot of parasites, the deal is that they, through this evolutionary arms race, have just found ways to evade the immune system, to just make the immune system things it's not even there. And then other times it's more about like, and I'm going to make this sound super anthropomorphic, and it's not like a decision that the body's making, like it's thinking about it like a person, but this is a process over evolutionary time. But so these worms that are living in the nurse cells, is it worse for the body? to deliver a tiny amount of energy to these teeny, tiny little worms, or to kill the worms

and calcify it. And if it's in your diaphragm, you know, so like that sandy diaphragm, yeah, it's a problem for the scalpel, but probably a diaphragm that's that hard isn't doing a very good job of like helping you breathe. And so if you end up with all of these calcified muscles and when a parasite dies, it usually kicks off an inflammatory response. And so I think over evolutionary time, the trick isn't attack all the parasites that you have with your maximum ability, because when you initiate an immune response, that often causes damage to the host as well. And so I think it's a balancing act between what do I just ignore and what do I have all out war against? I don't know, Kelly, I think you're just a shill for big parasite. I mean,

you're telling me I should happily live along with these things that have like squatting in my cells. You're like, isn't it just best for everybody if you just give in? and give up some of your energy. Like, I don't know. I think we're in all-out war with these things. There are some unpleasant people in my life, and I think my life is better for ignoring them than for, like, trying to attack back.

And, you know, I don't think it's that different with the worms. And, you know, we should have a whole episode one day on this old friends or hygiene hypothesis. Are you familiar with this idea? Yeah. The idea is basically that, like, we've had these organisms in our body through enough evolutionary time that our immune systems have come to sort of, like,

expect them to be there. and now they're sort of used as cues for how our immune system should work and how our immune system identifies self from not self. These things don't always go in the direction you'd think. I wouldn't want to have any worms in my body, but it's also possible my body is just like it's not worth the effort. You just ignore. Yeah, and Katrina is big on not classifying microbes,

some of them as good or bad because they all play different roles and it's complicated. And, you know, you might imagine you don't want to be infected, but obviously lots of microbes are essential for your life. the fermentation that happens in your gut, all that kind of stuff. Is it possible that parasites like these worms are playing some positive role that we're benefiting from? I mean, you call them a parasite, which implies that we're not getting anything.

There's no commensural reaction here. But are there any benefits to having these worms live inside of us? I don't think there's any documented benefit from having Trichinellus Borales inside of you. There are some other parasites that people have been experimenting with where when you infect people like their hay fever symptoms go away or their Crohn's disease symptoms become less severe or their MS goes into like remission or whatever the right word is for that. But those studies are super complicated. Sometimes you get good results. Sometimes you don't. It seems to depend on the parasite genome or maybe the exact person's genome and the exact kind of problem they have. And I think science is like really

working through digging through that right now. And right now we're at a like, what is happening? phase, but we should invite an expert on one day to talk about that. I'm just trying to get mentally prepared because, you know, I've learned now that bacteria can be good for you and even leeches can be good for you. So, hey, maybe in the future we'll all be intentionally injecting worms into our children. There are a community of people who are intentionally infecting themselves with parasites right now. I think most of them are not doing that to their children, I hope. But in my mind, the ideal thing isn't that we all take like five hookworms for breakfast and call it a day, but that we figure

out what cues the parasites are giving our immune system and then we can like take a probiotic pill or something that like replicates those cues so we don't actually have to have the parasites there. But I agree with Katrina that I think we are at a point where dichotomizing things as good and bad, we're realizing sometimes it's a little bit more complicated and it depends on context. And I think the point you made is really interesting that we can learn from them how to manipulate our own bodies. Like if they have spent millions of years evolving strategies to pull chemical levers inside the body, we can take advantage of that, right? If we understand the techniques that they have stumbled into, we can maybe use them intentionally to understand the workings of our own

system. Yeah, yeah. Sometimes the parasites that manipulate host behavior, we sometimes refer to them as evolutionary neuroscientists. And there's, you know, like a whole group of people like me who write our NSF grants about how we can understand host behavior better by trying to figure out what parasites have quote, unquote, learned through natural selection, all of this across all these years. So these guys, set up home in these nurse cells, make them work for them. How long do they hang out? Like, do they live as long as the cells live? Do they have like generations and generations of worms inside one cell? Or is a single worm last a long time? Yeah, so there's no reproduction happening at this stage. But worms can live, it looks like, for 25 plus years. 25 years? Oh my gosh. So they can

vote and, you know, buy alcohol and stuff like this? Yeah, absolutely, because that's what they're doing. But no, they live for a really long time. And I mean, they've got like a nice, setup. You know, food is being delivered to them. Their waste are being removed. So, yeah, they can live for a really long time, but they're not reproducing. They're just, like, biding their time until the muscles that they live in get eaten by something else. And are they squirming around a lot? Because for some reason, that makes them a lot worse. Like, if you're just quietly hanging out inside my cell and stealing some food, okay, but if you're, like, squirming around, then it's, ooh, I just can't tolerate that. You know, I would like to

exercise every day. So I guess I hope that they're, like, running laps in their little nurse But I think they're generally not moving much. And if they are, you're not feeling it. See, you're pro-parasite. There you are again. Like advising the parasites, how to live their best life inside people. Well, you know, we all need to stay healthy. So, you know, you might be asking yourself, if you want to avoid being a track for parasites,

how do you do that? Yes, tell me. For a long time, it was difficult. So most of us get this parasite from pork. And so pigs get infected. It's in the pig's muscles. and if you eat pork that hasn't been cooked through enough, that's how you get infected. And pork, you know, in the 1880s, the United States was like a world exporter of pork.

It was a huge industry for us. And it ended up being a big problem for us because Europeans decided that because we weren't checking for trichinella, we weren't checking for this parasite, that we were causing a bunch of trichinolosis outbreaks in Europe. And so for a while, they stopped importing pork from us. And this was a big problem for our industry. Some Americans went over there and they were like, no. And they figured out that like, no, it's not necessarily our pork that's causing the problem. Like maybe sometimes it's American pork.

That's the problem. But like it's not like all of our pork is wormy. But, you know, it was a good goal to try to reduce the worminess of our meat. And so how did we do that? But wait, hold on a second. Why pork? Like, do these parasites prefer pig cells to cow cells for some reason? Do cows have the kind of muscles that they can't get?

inside? Why pork? Okay, so part of it has to do with the animal's diet. So pigs eat everything. Like we are thinking of getting pigs on our farm so that all of our food waste goes into pigs. But then I couldn't turn them into bacon because they'd be like friends. I'd probably named them Wilbur. So pigs eat everything, including other pigs. Pigs are cannibals. Yep, pigs are cannibals. Yep, I knew you'd be excited about that. So when a pig dies, another pig will eat its infected muscles and then they'll get infected. So part of it has to do with diet. There were also some like rodents who would eat dead pigs and then other pigs would eat the rodents and so for a while rodents were part of the transmission cycle here cows tend to not eat meat but like horses can get

infected and horses don't usually eat meat but sometimes they will so like a lot of animals that we think of as non-meaters will eat meat every once in a while if you give it to them and they're in the right mood and so there have been cases of horses getting infected we even learned on the podcast recently that bees sometimes eat meat, right? That's right. Yes. Yes, meat, honey. Yeah, and so I think the reason that cows often don't get infected is because they're just not eating meat. I see.

So trichinella Sparales is one trichinella species. There are other trickenella species that seem to specialize on other animals. There's like in the United States, bears and moose and wild boars. Some of them can get infected by trichinella spirales, but there's also other trichinella species that are more common in nature that they can get infected with, but then we can get infected by those if we don't cook the meat through. And so there is some chance that I carry some trichinella in me because I ate bear once that I don't think was cooked through all the way.

You ate a bear? What? I had to hear that story. When did you have a bear? Not a whole bear. I was working with some folks in the Wisconsin Department of Natural Resources, and they were nice enough to invite us to their annual social gathering and a bunch of people brought stuff that they had hunted and there was barbecue bear and so I mean I've eaten bear I'm gonna assume

they cooked it through all the way but I've also eaten smoked moose heart oh but it shouldn't be in the cardiac muscles so that should be fine because it's in skeletal muscles yeah there you go that's not weird at all smoked moose heart knowing is half the battle no the smoked moose heart was gross. Like when it got pulled out of the bag, it still had, like, fat on top of the heart, but it was like a collaborator of mine who was from a part of the world where this was, anyway, I pushed through. You're going to turn me into a vegetarian, Kelly. Again, right? Back to your vegetarian roots. Exactly. Here we go. So let's back up. Okay, so you know you can get it from pork,

but you don't get it from pork in the United States much anymore. So what changed? So in the 1950s, we made it so that people were no longer allowed to feed their farmed pigs uncooked garbage, which is such a gross phrase to hear, I think. You have to cook your garbage if you're going to feed it to pigs? Yeah. So, like, you know, nowadays factory farms don't feed pigs anything you would just call garbage. I mean, I guess maybe people would want to call it garbage, but it's not actually garbage

the way these animals were being fed garbage before. But for a while, the change was just you had to cook it through. And if you cook it through enough, then any of the infective stages of the parasites are dead. And so that was a stage of improvement. all right so barbecued garbage is okay or slow roasted garbage as long as the internal temperature in the middle of the garbage reaches 165 degrees Fahrenheit yes you're probably fine maybe a sous vide then because that's really good temperature control suvied garbage that's where they serve at pig restaurants oh so disgusting so like up until 1985 we weren't really sure how pigs were mostly getting infected but you know we've talked about how cannibalism and rats contribute to infection that was also like sometimes if pigs and wildlife were interacting. I think most often the pigs were infecting the wildlife,

but sometimes the wildlife could infect the pigs. But once we sort of figured all of this stuff out, we were able to say like, okay, first of all, you have to make sure your pigs aren't able to eat the other pigs if they die. You have to make sure you don't have any rats in with your pigs, which I'm sure is hard. Yeah, that sounds hard because rats are everywhere. Oh my gosh, yes, we live on a farm.

Rats are everywhere. It's hard to keep them out, but you need to make a good effort to do it. Well, let me ask you, how do you feel about the rats? Because I have this policy, no rats inside the house. But outside the house, like, hey, you guys were here before us. What am I going to do? Kill all the rats? That's impossible.

Well, okay, so the rats that we had in our chicken coop were an invasive species. So they didn't really belong there. These were like the lab rats, Norwegian rats that had gotten out. And rats, like, usually I agree, but so that we have really stupid chickens. And, like, the chickens would be eating at their feeder. and the rats would be like right next to them eating and they'd just kind of look at them and be like, hey, Frank, and they wouldn't do anything.

But so then the rats were living in the rafters above and they were just like defecating an incredible amount. They do that. They do that. And there are some diseases you can get from rat feces and from mouse feces. Haunted virus. Yeah, right, exactly. And so if it's just like, yeah, I try to never kill wildlife

because I agree you were here first. But when it's like, well, if my daughter goes out to bring the chicken's food and she's going to get haunt a virus. Like, we've crossed a line and we have to get rid of the rats. Also, wait, you live in Virginia, which is not that far from the NIH, right? And you're talking about rats that have escaped from labs. Are you basically living the rats of NIM? That was a great movie.

These rats, they are the species that we use in the lab. I don't know that they escaped from the lab. They could have just, like, come off of ships or something. Keep telling yourself that. Science has made some mistakes, no doubt about it. I'll own up to that. Well, we had rats as pets once, and rats are wonderful, wonderful pets. They're smart, they're affectionate, they're really cute.

They do poop everywhere, though. Yeah, that is definitely a problem. I also had rats as pets when I was a kid, and I thought about getting one again the other day because I did used to love just having, like, a little rat on my shoulder. They make these cute little noises when the, yeah, I like rats a lot. My daughter would bike around the neighborhood with a rat in her hood of her hoodie, riding along with her. It was super cute. Yeah.

Anyway, you're saying if you have pigs and rats, try to keep the pigs from eating the rats. Yes, try to keep the pigs from eating the rats. And so once we figured this stuff out, it became clear what you needed to do to keep the pigs from getting infected. And once you knew what you needed to do, you could pass laws to make sure that people are doing these things. And by putting in the right sort of like procedures in place and then coming up with some better ways to test meat to see if it's working, we have managed to mostly eradicate this parasite. in pork from factory farm. Amazing. But there's still some ways that you can get it,

which we'll talk about after the break. More nightmare fuel. Don't worry. That's right. December 29th, 1975, LaGuardia Airport. The holiday rush.

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Only you can prevent wildfires Brought to you by the USDA Forest Service Your State Forster and the Ad Council We were just talking about how pigs from factory farms in the United States tend to not have this parasite anymore. And actually, in 2024, there was a study where they sampled three million pigs. And none of those pigs from factory farms had trichinella. Amazing. Wow. That is incredible.

Like, if you think that we have gone from one, and six people in New England having this parasite infection, which can kill you sometimes to testing three million pigs and none of them have it. That's an incredible decline. That means all those people who were infected when they died, nobody ate them and then absorbed the infection, right? Including the pigs. That's right. Yes. I should have known you were going to go there. My bad. But yes, that means that there's not a lot of human cannibalism going on. Good news. And, of course, I'm going to ask, if pigs can get it from eating other pigs, that means humans could get it from eating other humans, right? Yep.

Yeah, okay. One more reason not to eat your children, yes. Yeah, well, you know, if they're young enough, maybe they haven't been exposed. Move it on. When their meat is still so tender. Oh, God. Why do we do this? All right.

So now there's about 15 confirmed cases in the United States a year, which is an incredible drop. And there's about 10,000 cases recorded throughout the world per year. year. And I think a lot of those cases are in places like China where they eat a lot of pork, but maybe they don't have the same sort of procedures in place to make sure that the pigs aren't eating each other or aren't being exposed to rats. And so there are other places in the world that you can go where if you eat pork, you could get infected. So how is it happening in the U.S. if there were no examples in all of those pigs where people get and they're just getting it from the wild again or they're eating weird smoked moose hearts or something?

So I think a lot of people do get it from animals that they hunt. So you can get it from bears, you can get it from moose, you can get it from wild boar. And also, you know, if people have pigs in their backyard, they are not necessarily following all of the rules that, like, the USDA mandates. So it could be that their pigs are encountering wild animals that they're eating or then eating each other. And so you could get it from like backyard pigs. The good news is if you cook your meat, where the inside reaches, I think it's 145 degrees Fahrenheit, then the parasite dies.

The bad news is if you freeze the meat, even for something like two months, that doesn't necessarily kill trickinilla. What? You can survive freezing? It's amazing. Yeah, so there have been cases where meat has been frozen and two months later it's come out of the freezer

and when it thaws, those worms start moving around again. This is mostly the wild strains or the wild species. maybe it's not too surprising because like bears can hibernate, they get really cold. But still, the fact that they can freeze, that's amazing because bears aren't freezing through when they're hibernating. Yeah, and I thought that most cells, when they freeze, they burst because water expands as it freezes. So how do these guys survive it?

I mean, I'm guessing some of them do have nurse cells that burst and they die. But most of the food that we plan on eating, we freeze quickly because when those cells burst, that food doesn't taste as good. And so, like, you want to freeze your food quickly so the cells don't burst because that's a better way to eat a hamburger or a bear steak. So I think, you know, the parasites are benefiting from that and they can survive. And then also if you prepare jerky out of bear meat, that process is preparing the jerky doesn't always kill the parasites. These parasites, you think about it, like they transmit when the animal that they die in gets eaten by something else. And that doesn't always happen immediately.

So they need to be able to, like, survive the death of the animal for a while and persist in the environment to increase the probability that they get eaten by something gross. Yes. Yeah. So most of the cases in the United States come from wild animals that have been killed and then not cooked through all the way. In other parts of the world, you can get it from pork because they don't have the, like, public health procedures that we have in place here in the United States. But I'm excited about this system because it's a pretty clear example where doing the basic work to understand the life. cycle, the parasite, and then putting that information in the hands of people who can, like, set up procedures was able to save, I think, many, many lives.

Yeah. And also just be less creepy. Like, maybe not a lot of people were going to die, but it's really nice to know that we don't have, like, parasites running laps in our diaphragms in the United States. So you're a parasitologist. You know the cutting edge of parasite science. We've mostly told the historical story today. but like what are people working on right now if you go to trichinosis conference what are the

presentations about what are the questions that people are asking yeah so one of the main topics here is trying to figure out when an outbreak happens so there are still outbreaks i was listening to someone's talk the other day and it was somewhere in scandinavia there was an outbreak on farms and it showed up in a couple different farms and so they were collecting samples of the parasite and then they were genotyping it. So they were getting like the whole genome of the parasite. And they were trying to use that information to find out, did the parasite jump from a wild animal? You know, were the pigs able to go out in the fields one day and they ate a wild animal and that's how they got infected? But by figuring out what species or strain, then they can try to figure out like where the

procedure for keeping this parasite out of our food system, like where that broke down. And so they're using genetic information to sort of do the tracing stuff here. They're also still trying to to figure out how this nurse cell works, you know, how does it manage to manipulate the human body into essentially like waiting on it hand and foot without killing it? And, you know, also like wildlife ecologists are probably interested in what Trichinella is doing to like wild bear populations and stuff like that. So I think those are the main topics we're dealing with right now. So this all sounds surprisingly positive. You were saying this is a success story. Is this typical, Kelly, or is the wider world the parasites a darker world?

Well, the wider world of parasites can be pretty dark. So this was a nice case where we figured out how the parasite was transmitted. It was pretty clear what we needed to do, and it wasn't that hard to implement the changes. But there's other parasites where we know what it would take to eradicate the infection. But like, for example, bringing the appropriate sanitation measures to the people who need it has just proven to be something that we can't seem to do yet. And so the next time we talk about this wormy world of ours, we're going to be talking about NEM. nematodes, and today we talked about a nematode too, but we're going to be talking about nematodes that you can get because they burrow through your skin when you're walking in soil

that's carrying these infective stages. Oh, no, so you don't even need to make bad eating decisions. You can just be going for a walk. Or you can be gardening. They're able to just sort of burrow through your skin. So we will talk about soil transmitted helmets, which have been stubborn and hard to eradicate the next time we visit this wormy world. There's always more nightmare fuel waiting for you in biology.

Kelly's got it ready for you. Thanks, everyone. Tune in next time. Daniel and Kelly's Extraordinary Universe is produced by IHeart Radio. We would love to hear from you. We really would. We want to know what questions you have about this extraordinary universe. We want to know your thoughts on recent shows, suggestions for future shows.

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