Professor Yokogawa casually spoke to me jokingly, saying, Yoshino, as Tenia solium is present in your home, Okinawa, how about doing experimental infection for your PhD study. Of course, Yokogawa and I knew epilepsy and neurocysta sercosis could be caused by accidental ingestion of eggs of this parasite. At first, I was very nervous about accidental neurosiste sercosis in my brain, et cetera. However, it was an exceptionally big chance for
me to do an experimental infection. Even if I had a serious health problem or sudden death, My data might contribute to this topic that nobody has done and therefore be highly informative for future advances in parasitology. Then I felt some power inside of my body which pushed me to do it right then, and I swallowed three sister serki. When I came back to my home in the evening,
I told this mission to my wife. She was very surprised, but tried to understand my hard academic life and took more care of my health as my purpose was observing gravid proglotids and feces. I stopped using toilets anywhere, but kept a portable toilet and chopsticks for looking for gravid proglottids and collected them all every day for three hundred seventy one days.
I love this first hand account.
I love it.
I love it so much erin it's okay, let me tell you where it's from, because I stumbled across this and it just proved to be so much deeper that I that I had expected. Okay, so that is from ETO at All twenty twenty. The paper is titled Kozen Yoshino's Experimental Infections with Tenia Solium Tapeworms an experiment never
to be repeated. And this paper goes into this experiment that Yoshino did back in the nineteen thirties I believe, or late nineteen twenties, with this experimental infection of tapeworm and then the resulting papers that Yoshino published on the subject. And it's a really interesting paper. But yeah, I just I loved that description of like this, well, to do this and even if I die, the data will be useful, like right.
The description of feeling like a little power and then just like doing it, I love that.
Yeah. Yeah, ah well, Hi, I'm Aaron Welsh and I'm Erin Almann Updike and this is this podcast will Kill You.
And today we're talking about tapeworms.
Tapeworms.
Yeah, yeah, it's gonna be fun to see how this one shakes out. Erin, I have no idea what you're going to talk about.
I know nothing about how tapeworm biology works, and so it's gonna be interesting. But I'm excited for it.
It's gonna be fun.
And I'm also excited because guess what time it is.
It's quarantine any time it is.
What are we drinking this week?
We're drinking Brave New Worm.
I feel like in one of our Wormy Parasite episodes we talked about how we're just gonna do like worm worm pun worm world puns. Yes, Lydia point on And I actually really like the name for this, and I think it fits tapeworms because Tenia tapeworms the ones that infect humans part of their host switching abilities and being able to find a new host. I feel like it's encapsulated in the name Brave New Worm. I love it.
I love it. How poetic Karin.
Yeah, and in Brave newworm is gin lemon juice, Earl Gray tea, a little bit of honey, simple syrup, and then garnish with a piece of lemon that you cut in the shape of.
A worm, like a really long tapeworm. Preferentially, Yeah, we'll show pictures and we'll post the full recipe for that quarantini as well as our non alcoholic plusy Brita on our website This podcast will kill You dot com and all of our social media channels.
And on our website This podcast will kill You dot Com. I've got my post it note here, which will tell me that you can find the sources for this episode and all of our episodes transcripts, recipes, bookshop dot Org, affiliate account, Goodreads list, music by Bloodmobile, merchandise, Patreon, and alcohol free episodes.
I want everyone to know that Aaron was genuinely looking at a little post it note in her eyes kept flicking back and forth to read the post it note, and I really enjoyed it.
You know what, There's only so much I can fit into my brain, unlike a given evening that we're recording, and post it's really helped me.
Speaking of post its, shall we refer to our notes.
And great segue. Thanks.
Thanks, I try and dive into this episode.
Let's do it. I'm excited right.
After this break. There are quite a few different species of tapeworm. As a general rule, there's a lot, but there are a few different species that can infect humans. Those are which we're going to be focusing on today. Some of these species infect humans because we are evolutionarily the definitive or final host for adult worms, and some of which infect us incidentally, either as adult worms or as the intermediate stages, which I'll get into in just
a minute. Plan for this biology section, we'll see how this turns out, was to just talk very generally about tapeworms as a group, because I think the broad strokes of their life cycles are not only so fascinating, but we can also cover a lot of ground by keeping things pretty general. And then I'll focus on a couple of species of tapeworm in particular that for humans stand a little bit apart.
That makes sense, Let's do it.
So tapeworms are fascinating, almost adorable little creatures. Sure, some of the scanning electron micrographs are like kind of cute, Okay, Tapeworms are flatworms in the phylum platy Helmentes in the class Cestoda, so different than the other flatworm friends that we've talked about on this podcast, the flukes which are the causative agent of schistosimiasis, and tapeworms are an entirely parasitic class of animals, which is awesome in and of itself,
and in general they have fairly complex life cycles, much like the flukes that cause schistosimiasis. So let's go over it first. We'll start with the eggs, which are passed in feces, so in poop, the eggs enter the environment and then have to first be ingested by an intermediate host. Now, this intermediate host can be anything from a copapod in the case of something like a fish tapeworm, to a pig or a cow in the case of various species of human tapeworms, or a sheep or a rat in
the case of like a dog tapeworm, et cetera, et cetera. Right, and in these intermediate hosts, in general, the eggs leave the guts of those animals and mature into a larval or immature stage which insists, so they tend to form these little cysts in various organs in the body, like the liver or the muscle or whatever, and then they hang out in these intermediate hosts, often not causing too much harm, although sometimes they might hasten capture by a
carnivore in some way, like maybe making a rat easier to catch by a dog, for example. And then these cyst stages have to be ingested by their final or definitive host, and once they are they exist in the guts of that definitive host. They mature in vertebrate guts into adult tapeworms. Gennero.
So can we talk a little bit about the cyst sure?
What would you like to talk about?
What is it made of?
Like?
Is the growth of the tapeworm just completely arrested? Like?
Is it? Great question? It depends on the species, but in general no. So the cysts are little little baby tapeworms. They have a little head and a little skull x that's what the head is called. I'll talk about it in a second. And then they have like a part of a little body, and then they have just a little structure around them, which is what entraps itself in say the muscle or the liver of the intermediate host, and it.
Does that to evade the immune system exactly.
So these cysts tend to be very good at evading, especially vertebrate hosts immune responses. They just can hang out there for in some cases quite some time, like a number of months or even years, just waiting to be ingested.
And then another question about these cysts, I just I'm so fascinated by yeah, by these cysts. So if the intermediate host dies with this, with these cysts, you know, throughout their muscle, how long in the environment would they last? Would there be scavengers that could come in? Like, how would that work?
That is a very good question. I don't fully know the answer, and I expect that it varies quite a lot depending on the species. But in general, this is something that usually needs to be ingested while it's alive, So it would be a lot of times it's carnivores that are the kind of definitive host of these creatures, or in the case of like fish tapeworms, if fish are ingesting copa pods and things whole.
Right, Okay, yeah.
I want to talk for a little bit about the adult tapeworms. Because they're fascinating. So tapeworms will post a lot of pictures of them on our Instagram, So if you don't follow us, you should, because again they're very cool. They have a head which has no eyes, no light sensing organs, no mouth. Their head is often called a skulex, and it's just a set of hooks and or suckers that they use to anchor on to the gut wall of their vertebrate host and then attached to this little
head or skulllex. They have a skinny, little neck and from this neck they make their body, and their body is formed of a bunch of segments that are called proglottids. So this worm, what it does is it attaches by the hooks on its head to our gut wall and absorbs its nutrients through its body by just diffusion across its body. It doesn't have a mouth, what exactly, It has no mouth, just as our gut contents flow past.
They absorb whatever they need through their tegument that's their version of skin, and their neck is constantly producing more and more of these proglotted segments from like you can think of it as from like the top of the neck and then they displace the older proglottids down and down and down right. And so this tail of the body of this worm is just growing longer and longer and longer, reaching toward our anus right as it grows along our gut tract, adding more and more segments. Now
these proglotted segments. Each one of these segments has an entire reproductive tract, both like testes that make sperm and ovaries that are making eggs, and they self fertilize. It's amazing.
That is incredible, I know.
And as this worm matures and becomes longer and longer, adding these segments, the mature final segments that are fully fertilized, chalk full of eggs break off and are passed through the feces of the host and enter the environment. Chalk full of hundreds, if not thousands of eggs.
Interesting, So it's not a lot of eggs in your stool, it's this whole blotted for vlotted. Yeah, oh wow, I know, it's great, right, I My mind is just blown, I know, and I.
Know that that was a lot. So I'm going to just do a very brief recap of the whole life cycle of tapeworms. Ready, yeah, egg intermediate host eats the egg cysts in various tissues. Definitive host eats those tissues. Adult worm in the gut poops out eggs. That's all tapeworms in general.
A circle of life, circle of life. Okay, so this probably varies a lot from species to species. But how long do some of these eggs stay in the environment or can exist in the environment.
Great question. I don't have an exact number, but they are quite environmentally tolerant in gener so they can like dry out and still be potentially infectious, so they can live for a decent amount of time. Wow. Yeah, Now many tapeworm species really. I think some of the papers I read said that probably every vertebrate has at least one species of tapeworm that infects it. So there are tons and tons of tapeworm species, and that was a very general overview. We're going to focus today on just
a few of these tapeworm species that infect humans. Tenia solium, Tenia saginata, and Tenia asiatica, which is very closely related to Tenia saganata. These three are the main species of tapeworm that have humans us as a major definitive host. Tenius saganata is commonly known as the beef tapeworm because its intermediate host is a cow and we get infected from undercooked cow meat. Tenius solium is commonly known as the pork tapeworm because its intermediate host is a pig
and we get it from eating undercooked pork. Teenie asiatica also tends to infect pigs. Now, there are a few other species that are very important for humans as well, like Diphilobothrium latam at all. There are so many different species of Diphilobothrium. These are the fish tapeworm. These also can use humans as a definitive host, but they're not very species specific, so they can grow to adulthood in various other mammals and birds as well.
Okay, question about that one. Actually, yeah, so you said that in that genus that I'm not going to attempt to say die Philobothrium. You're doing great, thanks, But the fish tapeworms fish are the definitive hosts, and copopods are often the intermediate hosts.
Great question. They often have two intermediate hosts ahah have an even more complex life cycle, first little copapods and then fish, and then either a bigger fish, or mammals or birds a lot of times mammals or birds.
Cool cool, got it, Yeah, great.
Questionnairein so, let's talk about the symptoms when you get infected with an adult tapeworm. The thing about for humans, at least almost all these species of tapeworm, whichever of those four major groups we're talking about, is that these species that are well adapted to humans, when they infect us the way that they're supposed to as adult tapeworms in our guts, they really don't do all that much to us. That is, they absorb some of our food.
They can cause abdominal pain, maybe some cramping, some diarrhea. If the worm burden got to be really high, then they could potentially cause a bit more of a symptomatic infection, but it still isn't even on the scale of say something like hookworm that we've covered in the past, because they're not burrowing into our gut wall. They're just hanging on right, and they're not sucking our blood. They're just borrowing some of our food as it passes through our
small intestine before we get a chance to absorb it. Okay, Fish tapeworms have been associated with some anemia due to pour vitamin B twelve absorption because these worms attach in our small intestine and that's where we absorb vitamin B twelve. Interesting, Yeah, but even that is fairly rare, okay, And I couldn't find very great data on this, but I don't think in general, worm burdens with tapeworm tend to be quite as high as they can get with like hookworm anyways.
But the point is that, in a similar way that we actually saw with schistosimiasis, the severity of tapeworm infection comes not when tapeworms are acting the way that they're supposed to, but it's when they start acting a way that they're not supposed to. That is when we as humans get infected with the wrong life stage of the tapeworm. So when instead of being the definitive host, we become
the intermediate host, that is when problems arise. And it turns out that this can happen with a few different species of tapeworm huh. The pork tapeworm which I've already mentioned, Tenea solium, and two species of dog or canine tapeworm, A Chinococcus granulosis and A Chinococcus multilocularis interesting. Yeah, it gets so much more interesting. So first, let's talk about how this actually happens. So, humans get infected with adult tapeworms by eating undercooked meat of beef or pork or
fish that is filled with cysts. Right, So if instead of eating undercooked meat that has cysts in it and getting infected with an adult tapeworm, if we instead come into contact with the eggs of these tapeworms, that is, if we ingest anything contaminated with human poop or with dog poop, then we become the sheep or the pigs, and instead of an adult tapeworm in our gut, these eggs hatch in our stomach, become those adorable little embryos
and invade through our gut walls, travel through our bloodstream to our tissues, and insist themselves with the hope of eventually being eaten.
Does it ever happen where if you have an adult tapeworm infection and they're making those eggs, and they're making that little eggsac thing that that breaks open and you get insistement that way.
Oh do you mean auto infection?
Oh what a great question.
Yes, it absolutely can happen. Okay, that kind of is what in that first hand account when the author ate SISTA SIRTC guy, that is the intermediate stage. So they ate the intermediate stage in order to grow the adult tapeworm. But what they were worried about is accidentally becoming exposed to the eggs that they were pooping out.
Right, right, And so when someone has these cysts in their tissues, is it more likely that they got it from ingesting eggs from another source or from this auto infection?
Great question, I think in general, from any other source. One of the papers that I read said that about twenty five percent of people with neurocysta circosis, which I'll talk about that in a second, but basically with these cysts either had in the past or currently had a tapeworm. Okay, so that's a fairly low percentage, But that was just one paper. I think we don't have a great handle on how much auto infection happens. Okay, so we talk about why these cysts become a problem, and you probably
already know why. It's because they can insist almost anywhere. So in the case of Tinia solium, the disease that results from infection with this immature life stage is called cistus orcosis, and the symptoms of cistus orcosis can really vary because these embryos are traveling via our bloodstream and just they're finding their way anywhere that our blood vessels go, which is really anywhere. And you can find them insisted in muscle tissue, where most of the time they're asymptomatic.
You can also find them in subcutaneous tissue like underneath the skin. Which what's really interesting is that this tends to only happen from infections happening in Asia rather than in Latin America or Africa, and at least from what I can tell, this likely has to do with the genetic differences in the population of Tinia solium in these different areas rather than any human susceptibilities.
Okay, quick question, how big are the cysts?
Great question? Usually for tenius olium one to two centimeters or so.
Oh that's still bigger than I thought.
Yeah, not huge. Just wait, and these cysts tend to be present for just a few months to years, but eventually they do gradually disappear as the embryo dies, and then our body recognizes it and kind of just takes care of that cyst.
It's just tired of waiting around for you to be eaten by a.
Predator, right, it just can't hack it anymore.
And how long do adult tape worms live?
Oh, it really varies. Let me go back to where I had that, Deah. Some parasitology textbooks will tell you like twenty to twenty five years. Oh, but I don't think that that's it's thought that that's probably an over estimation from like anecdotal cases from a long time ago. So it's probably less than five years. But it's still like they're with you for a chunk of your life, right.
Yeah.
These cysts from tineas solium can also end up in the eye, where in the eye you can imagine they can actually cause quite a bit of damage, like causing visual impairment because they're blocking vessels, et cetera. But the most common and most detrimental place where this particular parasite tends to insist is in the brain, right. And when it insists in the brain, it's called neurocystus orcosis brain sisters orcosis, And what happens in the brain is very
similar to what happens anywhere else. These embryos make their home, they form these one to two centimeter cysts. They usually don't get much bigger than that, although they can. They hang out there for a number of months or years, and then eventually they degener our immune system wakes up and kind of notices these cysts for the first time
and in helping with that degeneration causes inflammation. So neurosystus orcosis can end up causing, as you might imagine, any range of symptoms in your brain, depending on how many cysts you have, because if you're exposed to tapeworms, remember these proglottids are filled with hundreds, if not thousands of eggs, so you could potentially be exposed to quite a large number.
It also depends on if these cysts are growing, because sometimes they do get a bit larger than one to two centimeters, and if they happen to be in the wrong part of the brain, that can cause blockage of the cerebrospinal fluid flowing in the brain, which can increase the pressure in your brain. But more commonly it's the end stages this inflammation, as our body is actually try trying to get rid of this cyst that causes symptoms
like headaches, like mental status changes, or like very commonly epilepsy. Right, And it turns out that neurosys to circosis is one of the most common, if not the most common cause of infectious epilepsy in a lot of parts of the world, which I totally didn't realize until doing this episode.
Yeah, can we talk worm burden or cyst burden. Do you have numbers for like the median cyst burden in someone who has, you know, neurosyst sircosis, or at what is there a threshold at which point epilepsy is common or is it really just depend on the placement of the cysts.
It's a really good question. I don't have good numbers on that. Really, we don't have good numbers on that, especially because as much as we have numbers on the percentage of cases of epilepsy, for example, that are caused by neurosyste yircosis, what we don't have a good handle on is how many people with neurosystem circosis, like with the cysts in their brain, actually have any symptoms at all, much less epilepsy.
That makes sense, So.
The only good thing to say is that in a lot of cases, even though this sounds like it would be very extreme having cysts in your brain. It's very often asymptomatic, which is fascinating in and of itself.
Yeah, is it just epilepsy, that's the main side effect.
It's not just epilepsy. It can be in theory, anything that your brain can do. So it can mimic a stroke, or it could even cause a stroke. It can cause increased intracranial pressure if it's blocking the flow like I said of that cerebral spinal fluid. It can also cause massive headaches. Really, it can do almost anything. But for some reason that I couldn't get a great handle on, epilepsy is one of the most common presentations.
And this neurosister circosis is it more highly associated with certain species of tapeworms more than others.
So neurosis orcosis is only from Tinia solium.
Okay, No, we're not. We don't have to worry about fish tapeworms.
Fish tapeworms nope, and feef tapeworm Nope. It's just the pork tapeworm.
Huh.
Now that's not the only tapeworm that can infect us as an intermediate host, right, I already said it kind of caucus species can also infect us as an intermediate host. Now here it results in an entirely different disease. Two of them actually high DADD disease or cystic kindo caucus and alveolar caucus. So with this it's a similar idea except for some reason. The cysts of a kind of caucus, first of all, tend to infect our liver, not our brain.
Why I was waiting, I was waiting so long for you to ask me why, Erin, I was waiting for you to ask me why do tenia solium go to the brain? Oh? Yeah, I don't know why, Erin.
You were waiting for me to ask a question for which you don't know the answer.
That's like most of our podcast.
I feel like.
I tried so hard to find the answer to this question, and I couldn't come up with a good one. The best one that I got was that in our brain, tenia solium is very protected by our blood brain barrier, so it's a good place with minimal immune response for it to hang out. But it kind of caucus if
we get affected with the intermediate stage. As it burrows its way through our gut wall, it enters our portal circulation, which brings it straight to our liver, just like it's just a semiasis you might remember.
Uh huh.
Another place that it can commonly end up is in our lungs, and in rare cases it can go other places as well. I know your face is well.
It's fascinating because it makes me think that the if there is tissue tropism, if that's been selected for, then does it have to do with the particular predator prey relationship that these species are a part of.
Yeah, that's a very good question. But really in pigs especially, you can find cysticerca in the brains of pigs, but really it's their muscles that are chock full. Oh right, And you can also find it in the liver, and you can find in other places. Now, with a kind of caucus in the intermediate stage, normally when it's not humans, it kind of caucus does make its home in the livers of sheeps or in the livers of rodents for the other species of a kind of caucus, so that
does make sense. In humans it goes to the same place. I know, it's very fascinating. I don't have a great answer, but I do want to tell you a little more about the cysts of a kind of caucus and the disease that it causes because it's totally different than tenius solium. Basically, these cysts. You asked earlier, how big do these cysts get? Yea, Now, with a kind of caucus, the answer is not one to two centimeters. The answer is that these cysts can get to be so massive that they are larger than
your entire liver. Oh no, because what happens with a kind of caucus. You also asked, how active are these little cysts? Like, well, it kind of caucuses. Quite active because it in fact reproduces and makes more cysts within each cyst, and that is how it continues to grow ew like.
A rat king of cysts. Yes, bide your liver exactly. So I'm guessing that there aren't many asymptomatic infections people.
People tend to be asymptomatic until these cysts grow so large that they start causing things like nausea, vomiting, abdominal pain. If these cysts are in the lung, it's going to cause cough, shortness of breath, chest pain. And what's really dangerous about these is that because each cyst is full
of hundreds if not thousands of tiny other cysts. If these have to be taken out surgically, it's actually very high risk because if you puncture that and you release those cysts, not only can that you know, infest you in a lot of other areas of your body. Those cysts can go on to like reinsist, but it also can just cause a massive immune response in us.
And is that sort of the issue with treatment in general?
Yes, great question. Treatment in general for adult tapeworms, treatment is very easy. It's like a single dose of an anti parasitic. But when it comes to neurocyst to yircosis or high data disease or a kind of caucosis, it is much more difficult to treat. Yeah, because you have to balance the inflammation that treatment is going to cause from your body kind of waking up and noticing these cysts with actually treating and getting rid of the parasite. Right, So it is a lot harder.
Yeah.
Yeah, that's the biology of a whole bunch of different tapeworms in very brief fascinating Yeah, I hope it wasn't too much messy now it was great, So Aaron, mm hmmm, I know nothing about like where these tape rooms came from? Or like why do we get infected with them? Like? How did we figure this out? How many people have dug through poop to get us here?
That's those are some great questions I will see what I can do to answer them right after this break. Okay, the history of tapeworms. To cover the complete history of all tapeworms, we would have to go back incredibly far and incredibly wide, like hundreds of millions of years all over the globe. But we're not going to do that today.
For the purposes of today's regular season episode. We're going to skip ahead to, oh, just a few million years ago, which is when the history of the tapeworms that I'm mainly going to talk about in this section, which are the three tenspecies that we already mentioned, it's when that history really begins. Before moving on to that history, though, I want to plug next week's bonus episode, because that is when we will get to spend a bit of time in the distant, way distant, far distant past, like
tens or hundreds of millions of years ago. And while we may touch on the early history of tapeworms and that up episode. Most of what we're going to be talking about is poop poop.
I can't wait. Oh, it's gonna be so good. Aaron.
When doing the research for this episode, the one that we're recording right now, I came across a paper describing tapeworm eggs found in the fossilized pooh aka copralte I've been saying it wrong for years of a two hundred and seventy million year old shark, which is so cool. I love it.
I love it so much.
I do too. And this got me thinking more about copra LTEs, which if you've listened to the podcast before, you know how much we love fossilized poop.
It's one of our favorite things.
It is. And I was and I was thinking to myself, Well, what else can poop tell us? What else can what else can these copper lights tell us? So I reached out to one of the world's leading experts on wait for it, dinosaur copra light.
I just I'm so excited.
Next week, doctor Karen Schin, who was just up the road from me at the University of Colorado Boulder, will be joining me to dive deep into fossilized pooh. What we can learn from it how it becomes fossilized, and which kind of animals are most likely to have their pooh become fossilized. So mark your calendars.
Which animals are most likely to have their pooh become fossilized? Right?
Is it carnivores? Is it herbivores?
Which is it?
I did? You'll have to wait and find out because I don't know the answer right now. Okay, But like I said, for today's episode, we're going to start a while after the dinosaurs, like a long while. Aaron, you asked. One of the things you asked was where did these things come from?
Oh?
And I'm so excited to answer. Knowing what you know about the common human tape work, those three Teeneae species, and what their life cycle looks like and which animals it involves, when do you think humans and tapeworms most likely became acquainted with one another?
My guess would be sometime when we started domesticating livestock.
Great guess. That's such a good guess, because you know teny twelve thousand years ago, that is when humans started to domesticate livestock. That's when you know a lot of parasite and pathogen exchange happened. We've talked about this so many times in the podcast.
Before, and I can tell by your tona that I'm wrong.
You are, but but that is what people thought for a really long time. They thought, Okay, it had to have happened when people first started domesticating cows and pigs in particular, and we picked up these tapeworms, then they were the ones that brought tapeworms to the table. However, it seems that it was actually humans that first gave these worms to their livestock. What what I know, I know.
Let's talk about why that revised version of events seems likely given some of the ecological, evolutionary and life cycle
characteristics of these tapeworms. Like we've talked about, the genus Tenia is chock full of species, just dozens of species, and we actually know quite a bit about the life cycles of many of the species in Tenia, which is pretty awesome because it means that we are more easily able to explore evolutionary relationships and historical distribution patterns and host associations, all those sorts of things, so we can tell when a species diverged or experienced a host switching event.
For example, like you talked about aaron, Tenia tapeworms have a definitive host, which is often a carnivorous or omnivorous mammal, and an intermediate host. The prey species also a mammal, and transmission primarily occurs in this predator prey interaction. And Tenie are actually unique in that they have mammals as both definitive and intermediate hosts, which I think is just a cool little tidbit.
Yeah, that is cool.
In the past, when we've talked about parasites, we sometimes talk about host specificity, how some parasite species are uniquely adapted to their host species, and how they can't complete their life cycle in another and maybe even the host and parasite have co evolved so tightly that you can mark host evolutionary events with parasite evolutionary events. But that does not seem to be the case for Tenia tapeworms in their carnivorous definitive hosts, who don't necessarily have these
super tightly linked relationships. Rather, it seems that which were are associated with which carnivores depends on where those hosts live. And who the intermediate hosts are in the ecosystem. So you could have worms switching between unrelated hosts like hyenas
and lions if they share the same ecosystem and prey species. Okay, And so the diversity of these tapeworm species is based more on ecological factors rather than on a phylogenetic or co evolutionary basis, which I think is really cool because you have to think about it in terms of ecosystems
and like who are the players in that ecosystem? Right? Yeah, And these hosts switching patterns and tapeworms are relevant for today because things like climate change or land use change can lead to these ecological disruptions where a new tapeworm species could suddenly be introduced to a new ecosystem and then into a new host And we don't know what the possible conceptquences of that might be. All right, but what is the relevance for the history of tapeworms in humans?
I'm getting there. Phylogenetic analyzes have shown that Tinia tapeworms and humans were well acquainted with each other long before humans were humans, which also means long before modern humans began domesticating pigs or cows, right, right, right, So how
did tapeworms and humans get to know each other? About two million years ago or so, early hominids in Africa began to incorporate meat into their diet, scavenging the kills of predators in the area, such as lions or hyenas, or later hunting animals themselves, and when they began taking the odd leg from an antelope or a rib from a warthog, maybe they also found themselves eating not just meat, but also some of those tapeworm cysts.
Honestly, it makes so much more like once you go through that logic, it makes so much more sense.
Yeah, it's so it's so interesting because I was immediately assuming, Okay, here's going to be another classic example of agricultural revolution, and yeah, but no, it's I just find that so fascinating. I love it.
It's just like once we became omnivores, boom boom, we get parasites.
And over time humans stopped becoming just this incidental part of the life cycle, but the relationship grew much stronger and closer. And so when humans began domesticating livestock, it was the long infected humans that brought tapeworms to their pigs and cows. Yeah, wow, I f fun And do you want to hear some evidence in supportiveness? I always okay. So, for instance, the sister species of Tenia solium is Tenia hyenae,
which infects hyenas and antelopes. What And the sister species of Tenia saganata and Tenia asiatica, which, like we mentioned our sister species with each other, is Tenia simbae, which commonly infects lions and antelopes. Oh what uh huh, it's so interesting. Genetic analyses estimate that Tenia saganata and Tenia asiatica probably diverged around zero point seven eight to one point seven to one million years ago, which is pretty close to the period when humans began switching from herbivy
to omnivary or like a little bit after wow. And Tenia Solium's estimated divergence is a lot more recent, about three hundred and fifty nine thousand years ago. And an interesting side note, some researchers have suggested that Tenia solium was maintained in some human populations via cannibalism. In addition to this less sensational prey hyena association.
I mean, I feel like that goes along with the fact that we can also serve as intermediate hostsoutely this parasite.
Yeah yeah, So long story short, humans gave tapeworms to pigs and cows, not the other way around, and they seem to have done so on three separate occasions, so Tenius aginata and cattle and Tenia asiatica and Tenia solium and swine. But those last two tapeworm species aren't closely related, which is why it was thought to be two separate introductions in pigs.
Right, which, like I know, that's just interesting in and of itself. Absolutely, yeah.
And once inside these livestock species, they were there to stay and spread, especially over the long period of exploration and colonization that began in the fifteen hundreds. But that's getting a little bit head of things. So let's see what the ancients have to say about tapeworm Shall we.
Shall we shall?
Unlike microscopic parasites or pathogens, wormy parasites are visible, like you can see the actual worm segments in your poop, and for this reason it was probably easier for people to make that link between a disease causing organism like the tapeworm and the symptoms of infection, even long before the days of germ theory. Imagine having stomach cramps and fatigue and then pooping out segments of something that looks
like a worm. It'd be hard not to say, oh, that's why I was feeling so cruddy these last few fortnites or whatever, And so unlike infections from microscopic pathogens, for instance, influenza, virus or plague, the first descriptions we often have of these paris diseases is actually of the parasites themselves, or sometimes the parasite plus symptoms, rather than the disease, which I find so interesting because I think it does change the way we think about the concept
of disease versus pathogen. Yeah, I don't know, something I was just thinking about. Given their size and conspicuousness. Tapeworms, of course, make an appearance in the Evers Papyrus from around fifteen hundred BCE, and we also have tapeworm infections
in the stomach and intestines of some Egyptian mummies. Aristotle in the three hundred s BCE described how some pig muscles appeared to have bladders or cysts that look like hailstones, and he also noted that adult pigs who were free roaming it tended to have the so called measled appearance, while nursing pigs did not. Pliny the Elder in the first century CE may have been the first to use the term tenia in reference to these worms, from the Latin word for flat band or ribbon and references to
the worms. I mean really, they can be found all over the world in ancient texts from China, India, and Middle East, just to name a few. But the ancients didn't quite have it all figured out when it came to these parasitic infections, especially in terms of tapeworms. They may not have understood, for example, how exactly you get
these parasites. Although the consumption of pork is banned in several cultures or religions which could have something to do with tapeworms, the oldest mentioned of banning pork comes from Leviticus and the Hebrew Bible from around six hundred to five hundred BCE. Have I read this on the podcast before? I can't remember. I maybe, Okay, well I'm gonna do it again and quote, and the pig, because it parts the hoof and is cloven footed but does not chew
the cud is unclean to you. You shall not eat any of their flesh, and you shall not touch their carcasses. They are unclean to you. How interesting, yeah it is, And of course the consumption of pork is also forbidden in Islam. It's entirely possible that tapeworms, specifically in pigs, were responsible for the span, but there are also several other parasites that could have contributed to the unclean and I will say unfair reputation of pigs.
Yeah, Plus, like you can get tapeworms from lots of other things, absolutely cows and fish.
And also not all possible symptoms of tapeworm infection were recognized as being related to the parasite, such as this epilepsy that can emerge later in life as a result of neurosis to pircosis, which was described in Hippocratic texts epilepsy,
but not in relation, of course, to tapeworm. Right, we haven't gotten to do a possible retrospective diagnosis of a historical figure in a while, so I'm excited to announce that a few Researchers have suggested that the epilepsy that Roman dictator Gaius Julius Caesar from one hundred to forty four BCE, that he began to experience when he was around fifty four years old, might be related to sister
circosis neurosisis tercosis. Who knows, but what is clear is that people didn't really fully know how this life cycle was completed and the role of pigs versus cows versus whatever, and so there was no reason to try to control these diseases, and so the parasites just spread and spread and spread, Especially like I mentioned, as widespread travel and colonization occurred with more tapeworms in circulation and the rise of human anatomists in the fifteen hundreds and sixteen hundreds,
it was really only a matter of time before people started recognizing the other primary way that tapeworms could infect you besides Intestinally they had seen the measled appearance of pig tissue had already been observed, but not so much in humans, and the first recorded cases of neurosisisircosis were described by Rummler in fifteen fifty eight and by Paniolus in sixteen fifty two, both of whom described the liquid filled vesicles that they found in the brains of their
deceased patients, and not terribly long after these vesicles were shown to be parasitic, like shown to have those tiny little worms, which I think is absolutely amazing.
I think it like in looking through so many pictures, like it makes so much sense that they were able to make these connections sooner, because these cysts are not just a fluid filled sack with nothing in it. It's a fluid filled sack with a tiny little tapeworm in it. And if you already know what tapeworms are and that they're in your guts, then it makes sense that they were able to make these connections.
That's really interesting, Yeah, exactly. And so yeah, they pulled one out and you can see, oh, that looks like a head. Oh that looks like suckers, right, so it must be a living thing. Although the debate was kind of on for a bit as to whether these arose spontaneously in your gut or in your brain or something
like that. Interesting, but in general, yeah, by the seventeen hundreds, people were trying to classify these different species, which is just so much earlier than we usually end up talking about in the podcast. Yeah, I think it's a really fun,
really fun thing. By seventeen eighty to the three species of Tinia that I've mostly been talking about, Tenia solium, Tenius aganata, and Tenee asiatica, these three species were differentiated, and ten years later, in seventeen ninety two, a Peruvian physician named Hippolito Unanue was the first that we know of to record a case of someone a soldier with
both an intestinal tape worm infection as well as neurosist pyircosis. Wow. Yeah, Even still, it wasn't fully recognized that the worm in someone's gut could be linked to those cysts in their brain until the eighteen hundreds. At that point, some German doctors floated the idea that the adult might also be the same species that causes those cysts. But how do you prove something like that?
Yeah?
Oh oh, well, if you're thinking like one of these German doctors, specifically the one by the name of Kuchenmeister, you would find yourself a quote volunteer no in his case, a few condemned prisoners, and you would feed them sausages and a noodle broth containing Tenia solium cysts from a pig. And then you just wait a few weeks for the
execution date and then perform your autopsy boom results. That's exactly what Kuchenmeister did, and in the autopsies he did find quote a small Tenia that was tightly attached with its proboscis to a piece of duadenal mucosa and nine other worms. Oh there you go, wow, question answered. All you had to do was just find yourself some volunteers, and over the next few decades, the life cycle of this and other Tenius species was more fully fleshed out.
And this classic TPWKY episode wouldn't be complete without an instance of self experimentation or more accurate self experimentation plus a few volunteers. This is what you heard in our first hand account. Basically, in the nineteen thirties, this researcher mentioned named Kozen Yoshino infected himself so that he could better study the life cycle of Tinia solium. I think it was actually for his dissertation wo and he published
six papers from it, which was pretty pretty impressive. True commitment. He go a lot more than I published and other good news. As far as we can tell, Yoshino never developed any signs of cistisircosis, and his experiment did show us and quite a bit actually about the different stages of infection, symptoms, life cycle, and the infection rate of
this parasite. Into the twentieth century, cistusircosis grew in prevalence in some areas and declined in others, especially in those places where food inspection or livestock feeding laws were enacted
to try to reduce transmission of these parasites. And prevention really was key because, like we talked about, treatment can be difficult, especially for the sisters rcosis, and treatment is still it's not that great, Like the drug that seems most commonly used today wasn't developed until the nineteen seventies, and it has nearly as many terrible side effects as earlier drugs which were questionable in their efficacy. Right Still, the side effects from this drug, however horrible, aren't nearly
as bad as an infection with tapeworms can be. Maybe it goes without saying after what you heard in the biology, or maybe it bears repeating, because let's talk about the tapeworm diet real quick. This last bit of history is maybe a little bit out of order, but I promise I'll bring us up to the present day at the end of it. Have you heard of the tapeworm diet?
Oh? Oh yeah, oh yeah, definitely.
I feel like I've heard it mentioned jokingly here and there, but I always assumed that that's exactly what it was, like a joke. Where would you even get tapeworm eggs? A tapeworm infection has to be bad for you. How do you get the worm out? It just seemed kind of ridiculous and a terrible idea through and through. But when it came time to do this episode, I wanted to dig a bit deeper just to see what was out There. Was this tapeworm diet based in anything real?
Who first got the idea and how did they implement it? To answer these questions, we have to go back to the Victorian era around eighteen thirty two nineteen hundred. The predominant beauty aesthetic during this time in Europe and North America was tiny waists, transparent skin, delicate features, rosy cheeks, red lips, and so on. And this aesthetic kind of coincided with the rising prevalence of tuberculosis, which can cause someone who is infected to have many of those features
because you're dying of this horrible disease. And I think we talked about the romanticization of tb in our episode.
Yeah, yeah, I remember that.
It also coincided with the rise of the temperance movement, which urged self restraint and a controlled diet with flavorless foods like this is kind of where Graham Crackers got their start.
Oh yeah, we've talked about that on this podcast before too.
We have. And the history of the thin ideal, the so called thin ideal, and the factors behind its rise is too much to cover in this one episode, but I just wanted to briefly describe how, over this period, especially during the Victorian era, body shape and size became tied to morality and the pressure to conform to these new beauty standards quote unquote, and societal expectations led people to seek ways that they could do that, anyway they
could do that. Or you could also look at this as people using these manufactured expectations to make money through wacky and dangerous exercise machines. A pamphlet on the chew and spit diet or tapeworm pills. In the later decades of the eighteen hundreds, various companies advertised a mail service where they would send you a few tapeworm eggs for a nominal fee. Which is funny now that I know more about the biology, that they would send eggs, So I have.
So many issues with this. Yeah, go ahead, Yeah, the idea you're saying is that someone would get an adult tapeworm to suck up some of their food so that they then lose weight. Right, that's the idea behind the tapeworm diet. Yes, yeah, so eggs is obviously not going to do that.
Nope, you're just going to insist.
Also, like, these are environmentally stable eggs, but you're not going to ship them across the world, like in the what year is this you're saying, seventeen hundreds, you.
Know, late eighteen h undreds, early nineteen hundreds.
In the eighteen and nineteen hundreds, You're not going to ship these eggs and have them survive the journey and even be infectious.
No, not to mention the fact that even if somehow you could give someone tapeworms adult tape worms, that's not going to they're not going to eat enough of your life enough, right, It.
Just could cause some like vitamin and mineral deficiencies.
You could have diarrhea and stomach cramps, you sure could. You could have fatigue. Yeah. And so that's the thing is that if we're talking about this in the late eighteen hundreds early nineteen hundreds clinical trials, it wasn't even like a glimmer in the eye of someone who it just it wasn't even remotely a thing, first of all. Second of all, these quote unquote tapeworm eggs may have just been placebo. They might have just been empty little pill canister thingies, yeah, or.
Like little little granules of rice.
Sure anything. And third, I also want to point out that somehow, despite the fact that you and I both he had heard of the tapeworm diet before doing this episode, it wasn't even very popular or like a big fad, so people weren't really doing it all that much. So yeah, so it made me wonder, like, why is this still around?
And the answer isn't. I don't know the answer, probably because like it does conjure up a very visceral image of a giant parasitic worm that's like eating your food, even though that's not what happens.
Yeah, yeah, I mean it is what happens, and that they can get to be quite large and they do eat your food, right, but it's not like that.
No, So yeah, I think that it's kind of a very interesting snippet of history that somehow has left an impact on popular culture. It has been referenced recently on reality shows, there have been news reports of people trying this out at home, which absolutely don't do, and actual super sketchy websites that claim to sell either eggs or
other life stages to help you grow an adult tape room. Yeah, but I think the fact that it's still known today really says more about just how much cultural pressure there is to conform to these certain manufactured quote unquote beauty standards that intentionally ingesting a worm could ever seem like a good idea. Not to mention, it draws attention to all these predatory people and companies out there that take
advantage of that. So anyway, the tapeworm diet, though a blip in the history of snake oil salesmen, still has relevance for today. And speaking of today, Eron, I say, I promised I would get us here, where do we stand with tapeworms? Oh?
I will hopefully answer that a little bit right after this break, So I don't. I don't have great numbers on overall tapeworm burdens. I'm just gonna say that one right out front, largely because, like we talked about, and like I said in the biology section, when humans get infected with adult forms, especially of Tinia sagnata Tinia solium tena asiatica, the symptoms are generally quite mild. So we just don't have solid numbers. World Health Organization on their website is.
Like, we don't track it.
We just don't. But suffice to say, these are incredibly, incredibly common parasites causing millions, tens of millions, hundreds of millions of infections worldwide. I do have some numbers from the fish tapeworm. Shockingly enough, a paper that I found estimated that up to twenty million people are infected worldwide with Diphilobothrium species. And that's just fish tapeworm, right, beef tapeworm, pork tape worm. These are going to be incredibly common
as well. H We do have some numbers when it comes to neurosyst to circrosis as well as high data disease or it kind of caucosis okay, because unsurprisingly these cause more severe infections. So the World Health Organization reports that worldwide, the number of people estimated to be living with neurosys to circosis, that is, the cysts in the brain, is somewhere between two and a half and eight million people worldwide. Oh my gosh, right, huge number and huge range.
Right.
The range is because this is an estimate that includes both people who are asymptomatic and might be symptomatic, okay, and in endemic countries. And the list of endemic countries is very long. This is a globally distributed parasite. It's estimated that up to thirty percent of people living with epilepsy have neurosystics orcosis as a potential cause of their epilepsy.
Wow.
Yeah, And in some underresourced, impoverished rural communities in these endemic countries, it's more like seventy percent of the burden of epilepsy is due to neurosystics orcosis.
I had no idea, I know.
And the World Health Organization also estimates that seventy five percent of people living with neurosisis orcosis are getting little to no treatment. I know, not great when it comes to a kindo caucus the other species, multiple species of parasites which we can be the intermediate host and cause severe disease worldwide, It's estimated that there are at least a million people. One paper I read said between one and three million people worldwide living with the various forms
of a kindo caucosis. Okay, so all of these parasites are globally distributed and incredibly common.
I have a question about cooking mm hmm. If you follow like the standards temperatures for you know, pork and beef and so on, does that kill the cysts?
Great question? Yes, sure, yes, okay. I also want to kind of emphasize that pork gets a really bad rap. But neurosisis orcosis is not caused by eating pork. It's caused by exposure to human feces that have the eggs of the parasite. So while pigs are an essential part of that life cycle because pigs are the normal intermediate host, it is not eating uncook pork that gets someone infected with neurocyst to orcosis.
That's very I think a really interesting and important point, and I didn't know that before doing this episode.
Yeah, and I think it's an important part because certainly you could have pig meat that becomes contaminated with human feces, especially if conditions are such that human feces is being used as fertilizer and then becomes contaminated in the pig meat, etc. That's definitely possible, but it's not the same as getting an adult tapeworm from the cysts that are in the
pig meat. It's a pretty complicated life cycle. Yeah, and so unsurprisingly, prevention of this disease is the best thing that we could try and do right and as all of the complex life cycle parasites that we talk about on this podcast, prevention of a disease, like any of these tapeworm infections, requires a one health approach.
One hell it does.
It requires that animals can be vaccinated and treated for these parasites. It requires that adequate sanitation for both humans and livestock and domestic animals is available. It requires treatment for humans. So these are very complex diseases, all of these to try and kind of get a handle on, and that's I think a large part of the reason why they're still so widespread. M hm.
That makes sense, but it also seems pretty crucial. Two and a half to eight million people I know, and.
I had no idea what a large share of the overall global burden of epilepsy was due to neurocystis or coosis specifically.
Yeah. Yeah, yeah, me either.
So we need to do a whole episode on epilepsy, because I also tried to look into like how epilepsy and then I was like, who.
Oh no, it's It's like it's on our list. Might even be on our list for this season, though I'm not entirely sure.
Yeah, but that is a bunch of species of tapeworm.
How about it?
How about it?
Are we ready for sources? I think? So, okay, I have several I'm going to shout out a few, so Hoburg, either as an individual author or Hoburg at all. There are a few papers that I really liked to understand more about the evolution of tapeworms. And then one that was really helpful for the history the human history was a paper by del Bruto and Garcia from twenty fifteen. I had a.
Number papers specific to Tenia infections. Paper specific to the fish tapeworm infections, as well as a couple on a kinococcus. But I also want to give a special shout out to a series of YouTube videos that I watched that were put together by the Robert Wood Johnson Foundation and
Stanford Medicine. They're available on YouTube and they're really great short clips and there's like one for each parasite species that we talked about, and they're just I really like them, so we'll link to that as well.
I use that for the pronunciation Yeah, me too.
That's how I found them and then I was like, Wow, these are really useful.
Yeah, listen to follow and leave us a review on Amazon Music, Apple Podcasts, or wherever you get your podcasts, and don't forget. You can listen to new episodes one week early on Amazon Music or early in ad free by subscribing to Wondery Plus and the Wondery app. Yeah.
Thank you to Bloodmobile for providing the music for this episode and every one of our episodes.
And thank you to the Exactly Right Network, and thank.
You, of course to you listeners. We love that you listen. We love making this podcast. Hope you learn some fun things about tapeworms.
Yeah, absolutely, and a special thank you as always to our wonderful, generous patrons. We love you and appreciate you so much. Okay, well, until next time, wash your hands, you filthy animals. M.