I contracted toxoplasmosis in my first trimester. I will never know how the doctor did not educate me or test me for it. I was not given the opportunity to prevent the devastation this disease would have on my baby. It had a lot of time to go unchecked and do a lot of damage. My daughter, Dana, was born six weeks premature with severe damage to her brain and her eyes. She is now twenty two years old. She has very little cortex to her brain, She has cerebral palsy,
She is blind. She has severe developmental delays. Dana requires our full care. She cannot sit unassisted, walk, talk, feed herself, dress herself, or toilet herself. My husband and I still change her diapers day and night. The toll on her body has been tremendous. She has had ten surgeries, two of which were so traumatic we almost lost her. She has a tube that drains excess fluid from her brain. She has a metal rod in her back to help straighten severe curvature of her spine so her organs and
lungs can continue to function. She has a pump surgically inserted to give her constant doses of a medicine to help her relax her muscles from further contorting her body, which, by the way, is only minimally successful. One hip was reconstructed, the other is currently dislocated. I hate what toxoplasmosis has done to my daughter. It has stolen the dreams I once had for her and from me. Our whole family has experienced emotional and financial strain. Yet through this all
we have loved this young lady. She is remarkably determined to endure. She laughs. She enjoys being a part of an active family life. Dana has a younger sister, Rebecca, who is in college right now. She is one of the smartest, wittiest, kindest people I know. Life has been difficult for her too. Watching Rebecca, I can't help but think of what Dana's life would have been like if her infection were caught early on. What would her future
have held? Oh my god. Yeah. That was an account by Janet Morel, who testified before the Illinois State Senate in support of Senate Bill three six sixty seven, which was the proposed Prenatal and Neonatal Congenital Toxic Plasmosis Prevention and Treatment Act Act. This bill would provide that healthcare professionals shall provide counseling for toxic plasmosis and testing for toxoplasma gandhiaye when providing care to a pregnant woman during her pregnancy. So that was part of her testimony.
Wow, h my god.
Yeah, it's a really it's really sad. It's very rough.
Rough.
Well, I'm Aaron.
Welsh and I'm Aaron Olman Updyke and.
This is this podcast will Kill You. This week we are covering toxoplasma gandhi I. Yeah, we are, which has been a pretty heavily requested episode. I think has it, Yeah, I think it has Yeah, And it's going to be a heavy one. It's going to be an interesting one. It's going to be all the things that you've come to expect from this podcast. Yeah, speaking of things to expect.
It's quarantine ey time.
It is erin.
What are we drinking this week?
This week we're drinking what the cat dragged in? What is in what the cat dragged in? Well, of course it's not a dead mouse, but that would be appropriate as well. It's vodka, some sparkling wine, a little Creme de violette and lemon juice.
Yeah, it's tasty. It's the big crucial thing. Crucial is that you rim the glass with pop rocks.
Of course, because they look just like kitty litter.
There you go.
We'll post the.
Full recipe for this quarantini as well as our non alcoholic plusy Burta on our website This podcast will Kill You dot Com and all of our social media channels, so follow us there for the full recipe.
And I think I want to cover a couple pieces of business which I just don't think that we have done it all pertains to live shows or live ish shows.
They weren't live ish like we were there.
Yeah, that's true. It wasn't like a full live show. We're not going on tour or anything like that. But we were lucky enough to go to both the University of Florida thanks to Nick Kaiser, and also to the University of Michigan thanks to Laura Haynes. Yeah, we met so many amazing people during both trips. It was really, really fun.
We had the most fun at both of those trips. It was super excellent. So thank you for inviting us, and thanks to everyone who came and watched.
It was so fun.
It was great. And also I recently, Aaron Welsh, I was recently a guest on a live show of a podcast called The Road to Now. Yeah. Yeah, it was super fun. So this is a really great history podcast and they came to Chicago recently and I got to be a guest along with Obama's White House photographer Pete Susa. So it's so great, mind blowing, so cool, surreal. But anyway, you can hear that episode of the live show on the Road to Now, So just look them up wherever
you get your podcasts. And we're also going to post a link if we haven't already by the time this comes out on our social media.
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We have a new merch including water bottle.
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Of soap new smells.
So check that out.
Just go to our website This podcast will kill You dot com and click on merch to find that.
Any other business, Nope, let's just dive right in. Okay, Aaron, tell me about the biology of toxic plasmosis. I just can't wait to do that we'll take a little break, all right. Toxo Plasma gandhii toxic plasmosis. I've been looking for to doing this episode ever since I was a guest on.
The per Cast. Oh yeah, yep.
We talked a little bit about TOSO on that episode. If you haven't heard it, it's really fun. But I didn't do any research on TOCSO before I went on the Percast, so I felt really silly because I didn't know the answers to a lot of questions. So I'm excited to finally, you know, have done some research on this, like, actually know what I'm talking about a little bit. It's still not an expert, okay, so polished amateur exactly.
That's a good description for like my life, I think.
Okay, So, Toxoplasma gandhii is a protozoan parasite, so like malaria or giardiam.
Oh you did a great job, thank you?
Is that condescending it up just a little?
So?
This is a single celled organism that's not a bacteria or a virus. Okay, yeph And this, when I learned this fact, blew my mind so hard that even though this is technically EPI I'm gonna say.
This up top.
Toxo infects up to one third of the entire world's population. Uh huh, one third of the globe of humans.
Uh huh. I know, I know.
That is just mind wild, it's so wild, Oh my gracious. Okay, So, because this is a parasite, we have to talk about its life cycle because it's more complicated than some other organisms. Okay, So, the main host of Toxoplasma gandhi is of course cats. Cats are the definitive host of Toxoplasma GANDHII, and when they get infected with this parasite, they poop out thousands and thousands of something called oocysts. That's the life stage that the cats poop out.
Okay, yep.
And after one to five days in the environment the environment being cat poop, so cat box or your sandbox where your kids are playing, or your backyard or pretty much anywhere in the environment.
These oocysts spoulate.
So then they kind of become infectious at that point. Once they spoulate, they can persist alive and infectious in the environment for years, really years, well at least a year, okay, for year, yeah, for months and year, depending on the environment, so they can get into the soil, they can get into the water, they can get on your vegetables, et cetera.
What's the ideal environment.
The ideal environment would be kind of subtropical, so not too hot, not too cold, although they can survive freezing, you know, no big deal. Yeah, but they do. They like we'll see in the episection burdens tend to be highest in warmer climates because they do persist better in warmer climates. Okay, So they get all up in the environment and then they're picked up by small animals, birds, mice, rats, generally things that cats.
Might like to feed on.
Once they get into these small animals, they are now called taki zo whites. So that's the life stage that infects small animals.
Okay, I want to make some sort of joke about taki but I tried.
I tried too. There's no good one.
So inside of a mouse, generally, the way that a small animal gets infected is by coming into contact with their mouth. So they eat some soil, they drink some water, they eat a piece of lettuce, whatever it is that has these tachisoites on them, and they get infected. Then these tachizoites burst out of the intestine of these mice or these rats, and they infect tons of different cells. So this is a parasite that is actually it has to be intracellular, so it invades cells inside of everything
that it infects. And these this life stage replicates asexually, so it just divides, and it does so really really rapidly and really profusely. So in the mouse, you've now got this parasite dividing and replicating and swarming through the tissues. Then they'll find their way into two specific tissues that they like to invade, muscle and brain.
Why do they like those two types of tissues?
Well, let's talk about it.
I like, how now you like you know me so well that you know what I'm going to ask pretty soon.
Most of the time doesn't mean I always know the answers, though, but here we can talk about it. So they find their way into neural tissue and muscle tissue. Once they're there, I'm going to first say what they do once they're there, Then we'll talk about why these are the tissues they invade. Once they're there, they insist, so they actually transform into yet another life stage.
The Brady zoite.
The brady zoite forms a cyst inside of the muscle tissue or the brain tissue. The cyst is surrounded by the animal's tissue muscle or brain, but then full of hundreds of these brady zoites. These continue to divide, but they do so much more slowly. Okay, okay, But then to complete the life side, these brady zo whites have to find their.
Way into a cat.
Right, so the cat is going to eat the mouse or the rat or the bird. What part of the mouse or the rat or the bird. Do cats definitely eat muscle tissue?
That makes sense?
Okay, So that's why they insist in the muscle tissue. Why might they insist in the brain?
Oh? I think I know the answer to this.
Oh yeah.
It turns out that Toxoplasmagondhia is a parasite that can exhibit behavior modification. So that means that it can actually change the behavior of the animals that it infects, which is it's really cool.
It is very cool.
It's kind of like blows the lid off of the whole parasite host dynamic in a way that is so sci fi. But also I think it's just a tip of the iceberg. Okay, I'm jumping the gun to it.
It is so sci fi, but it's something that's actually not that uncommon in parasites that are transmitted what we call trophic lely, so from one what we call trophic level to another. So if you think of like the pyramid of life with like carnivores on the top, carnivores are gonna eat herbivores, and herbivores are gonna eat lettuce.
Or whatever, right, primary produce, secondary producers, primary producers.
Exactly right, right, yea lettuce, and so in in parasites that are transmitted like through the food chain like that, it's actually not that uncommon for parasites to manipulate the behavior of that intermediate host like the mouse, so that they're more likely to be eaten by the definitive host, i e.
The cat.
In the case of mice and rats that get infected, what they do is not only do they seek out more rapidly novel environments, and they're less fearful and more likely to be in open areas where normally mice and rats are kind of like they stay hidden because they don't want to be eaten, for example, So infected mice and rats will seek out novel areas and explore more readidly.
And they have done studies that show that they're not only less afraid of cat smells like cat urine, they're actually attracted to smells like cat urine.
Yeah, isn't that Oh, it's really Yeah, it's it's almost unbelievable, Like.
When you think about that the parasite has evolved to be transmitted this way, and this is how, and so here's the reason why this happens, or a reason why this happens, is that only in cats can Toxoplasma GANDHII complete its life cycle because once a cat eats those brady zoites that are in the brain or muscle tissue
inside the cat, they actually undergo sexual replication. And only in cats do does Toxoplasma gandhi actually sexually reproduce, and then it produces those oocytes that the cat poops out, and then the cycle can start all over again.
Right, the parasite has to find its way back to the cat.
Yes, Yeah, so there's a huge amount of incentive on the part of the parasite to make sure that they make it into the cat.
Yeah, it's a. It's gorgeous, it's beautiful.
It is that being said, what about humans? Yeah, so that's the life cycle like in the wild or in whatever. That's how Toxoplasma gandhi evolved to exist. So what are humans? Are we the cat or are we the mouse? The mouse or the mouse. So it turns out that we can get infected with almost any life stage of the parasite. So we can get infected directly from those spoulated oociss
that cats poop out. So that means if we get in contact with cat poop directly, or with contaminated soil or contaminated water, or maybe contaminated vegetables that haven't been washed or cooked, then we can get infected with that first stage, those tachizoites. Okay, those are the stage that's
gonna invade tissues locally, that's gonna replicate really rapidly. But we can also get infected with those tissue cyst stages that would normally want to be eaten by a cat, the brady zoites inside tissue cysts, gotcha, So if you eat contaminated meat, for example, then you can get infected with that life stage. However, since we're not cats, the parasite can't complete its life cycle inside of humans.
We're a dead end host, just like in lime disease.
Just like in lime disease.
We're not contributing to the parasite life cycle. And like the prevalence.
Unless a cat ad us which does happen, could happen, Yeah, could.
Happen, and it definitely happened prehistorically for sure. Apparently cats are like a major, major predator of humans, which may are like of the ancestors of humans, which makes total senating.
Yeah yeah, okay, So in humans, then the main way that this parasite causes disease is in two main ways. First by invading cells and tissues, so it can cause direct damage in those tissues that it invades, and by forming tissue cysts in really important places in our body where you shouldn't have cysts full of parasites. Cool cool, cool, but yeah, okay, got it all right, So let's talk
about the symptoms that we see in toxicplasma infection. The good news is that the vast majority of people who get infected, something like eighty to ninety percent of people will be entirely asymptomatic.
That's it.
I for some reason, I expected it to be higher asymptomatic. You said eighty to ninety are asymptomatic.
Yeah, yeah, okay, yeah.
But okay, So even of those ten percent of people who maybe do show symptoms, the vast majority of those people will have a very non specific, self limited illness, so they'll feel a little sick, kind of cruddy. And the most classic sign of an initial toxoplasmosis infection is lymphatinopathy. So your lymph nodes get swollen, Okay, and that's pretty
much it. Those lymph nodes usually aren't very tender, and they can stay enlarged for like a month or so the vast majority of the time, So that's even if you have symptoms, the vast majority of time, that'll be kind of your only symptoms, So not that big of a deal in that case. However, in some cases, a primary infection can invade specific organs and then cause illness
in those organs. So if those tachisoites swim through and find, say your heart tissue, your heart is a giant muscle, so it wouldn't be surprising for them to try and find and insist in your heart muscle, then then you could get something called myocarditis, which just means inflammation of your heart muscle. If those tachisoites invade your lungs, you
might get anumanitis. If they invade your liver, a hepatitis. Okay, all of these are theoretically possible, they have happened, but they don't happen very commonly.
Is there anything so, I know, like immunocompromise is one big aspect of where this might happen more than others. But is there anything else that is like makes you more susceptible to organ invasion?
That's a really good question. So the only other thing besides immunal compromise, which I'll talk in more detail about in just a second, is potentially strain differences.
So there are a number of.
Different genotypes and strains of Toxopasma GANDHII, and there is some difference in virulence between those strains. How big of a role that plays is not entirely clear. Okay, but so yeah, for most people who are healthy, they will never have any signs of infection. But in people who are immuno compromised, especially in people living with HIV, toxopasma can be an extremely serious infection. The most common form of toxoplasma infection of toxoplasmosis in people living with HIV
or people who are otherwise immunocompromised is encephalitis. So that's inflammation of the brain. So here's the thing about toxoplasma. If you get infected, even if you're asymptomatic, it doesn't necessarily mean that you don't have cysts inside of you right now. But most of the time, your immune system is going to be able to keep those cysts kind of in check. They're never going to do anything, they're
never going to cause harm. But if you become immunocompromised, those cysts can reactivate essentially, and then you can get the encephalitis later on.
Okay, yeah, that's bad.
So you can, like if you have an immuno compromise, you could get sick with toxoposmosis from a primary infection like this is the first time you got infected, or it could be that you've had cysts in your tissues and now they're re activating because your immune system is low. It's really really serious. It's considered an AIDS defining illness. Toxoplasma encephalitis got it in a person living with HIV.
And then, of course, the other way that you can get infected besides eating contaminated meat, which by the way, is the most common way that people get infected.
But I do have to point out there was a study that looked at the rate or the prevalence of toxoplasmosis in people who were vegetarians and people who were not vegetarians and found equal rates.
Fascinating.
So, yeah, so it's very very clear that there are many different roots for exposure. Absolutely much much beyond cats is what much beyond owning a cat I should say is.
Yeah, owning a cat is generally not even alone, owning a single cat is not even considered a risk factor.
Then we'll talk more about the ecology of that and why that is.
Yeah, But the other way that you can become infected is congenital toxoplasmosis, which is what we heard about in the first hand account.
It is horrible.
So toxoplasma can cross the placenta and then infect the fetus. It turns out that this is most common if a pregnant person gets infected for the first time while they're pregnant. And what's interesting is that the risk of infection of the fetus actually increases with gestational age, So the later in a pregnancy that a person gets infected, the more likely it is that the fetus will be infected, but the severity of that infection is opposite, so it decreases.
So the earlier a fetus gets infected, the more severe the outcomes.
But the less likely they are to become infected.
Exactly right, so overall, without any treatment for a primary infection, So a pregnant person who gets infected while they're pregnant, the risk of congenital syphalis is between twenty to fifty percent, depending on when during their pregnancy they get infected, what strain they're infected with, likely, and how much they're exposed to probably as well. Severe infections can result in fetal loss,
so it can result in stillbirth or miscarriage. But other characteristic findings are things called choreo retinitis, which is inflammation of the retina and the choroid, which is basically like your blood vessels in your brain in your eye, sorry, not your brain, which can lead to blindness, hydrocephalus, which is the build up of fluid.
In the brain.
And intracranial calcification, which is calcium deposits essentially inside of your brain and then seizures in a baby. So yeah, it's really bad congenital toxoplasma.
Is it routine anywhere to screen?
It's not routine in most places to screen unless there is a risk for infection, so it's not universal.
And is it something where you could determine whether it's an active infection or a like something that you have been infected with the sister just there, Yes.
You can so in general, and I will say that pregnancy is a form of immunal compromise, so it is possible to have reactivation of cysts, but it's much less likely that that will result in congenital toxoplasmosis.
Okay, so it's.
Really that primary infection, like if you get infected for the first time while you're pregnant, that's when it's the highest risk for.
So it's like the tachizoites exactly right.
Yeah, but also even if you like ate pork that infected, so then you're getting infected with brady zoites, but it's just not from within your body reactivating, which is primary infection. Yeah, but yeah, we usually use zeral prevalence, so looking for antibodies, but you can tell based on the type of antibody and the amounts of antibody whether or not it's a primary infection or you were infected, say ten years ago or something like that. Okay, And the good news is
that there is treatment. The treatment is mostly aimed at that tachyzoite stage, that rapidly dividing stage, so it doesn't affect the tissue cysts directly mm hm. So that's kind of the catch twenty two is that we can treat it, but we can't really affect those tissue cysts.
But if there's an act like let's say for pregnant people, if there's an active infection, that's really the thing that needs to be targeted anyway it appears.
Yeah, and so for pregnant people, there's two different ways that we can treat it, depending on if we think the feeted is already infected or if we're trying to prevent the fetus from getting infected. So one you can treat just to prevent those tachizoites from kind of crossing the placenta and infecting the fetus, or if you think the fetus is already infected, you can give different drugs that actually help treat it within the fetus itself, and all of those are affecting the.
Tachisoite stage as well.
Okay, so yeah, I mean that's basically the biology of toxoplasmosis.
Oh okay, Yeah, it's a bad one. I mean I knew that it was bad, but yeah.
Yeah, So Aaron, how did we get here? Where did this thing come from? And why does everyone get infected? One third of all people?
I'll tell you after this quick break. So the actual written history of toxoplasma gandhi is just over one hundred years old.
That's it.
Yeah, like the written history of there's this disease that does this, there's this parasite that does this.
Wow.
Yeah, So this is going to be a really short section. Just kidding. It means, yeah, it's me. It'll never be a very short section. It just means I'm going to talk more about evolutionary history and other things that I'm just going to sprinkle throughout. Fabulous Okay, but let's get to the written history part of it first. In nineteen oh eight, the parasite was described for the first time. There were these two researchers working at the Pasture Institute
in Tunis. They were studying leshmaniasis, which is a disease caused by a different protosome parasite. They're trying to figure out what the reservoir host was and learn more about leshmanias, the lashmania transmission cycle, all of these things. And for their research they were using an animal called a common gundy, which I had no idea. I looked it up and it's like kind of weirdly cute. It's definitely not like that cute. I mean, that's horrible. We'll post a picture, yes,
of course. And so this is it's about the size of a guinea pig maybe, and it's a type of rodent that's native to northern Africa. Oh, it's super good at living in rocky deserts okay. And so they were looking at this the tissues of a Gundhi gandhi for parasites leshmania, and they found a partizan that they thought was lash mania, but they looked a little bit closer
and realized based on morphology, this is a completely different parasite. Awesome, So they named it Toxoplasma gandhi eye toso for the Latin word for arc plasma for former life gandhi I was a misspelling of the host the common Yeah, no way, gundi is how you spell the animal g o n d ii is how you spell the specific epithet of Toxoplasma gadie.
That is so funny.
Yeah, I love it when things get named for silly reasons like that.
I mean, it's one letter, but it's just kind of like, I never thought about gandhi I. I mean I just thought probably it was gonna be someone's name.
But yeah, wow, that is so interesting.
Anyway. Okay, So at the same time that these two researchers, who by the way, their names were Charles Nicole and Louis Manso. At the same time that these researchers were finding and describing Toxoplasma GANDHII in the common gundi, on the opposite side of the world, in Brazil, another researcher, same year, another researcher named Alfonso Splendor, was doing the same exact thing, like he found Talksopoasma gandhi eye, but he found it in a rabbit what instead. Same time.
So yeah, keep that fact in your head.
Ooh, is there going to be drama?
No, I mean not really. I will say that by and large Nicole and Manseaux are the two that get the credit for the discovery, and in large part because their finding was written in English and Alfonso splendor was His was written in Portuguese and not translated into English until two thousand and nine. And so this goes into the whole English as a dominant as the only scientific language and blah blah blah all the issues surrounding that. So wow, it's kind of interesting. He also didn't name
the parasite. He just said I found this parasite, okay, so that could have something to do with it too. But another thirty years would pass before people realized that this parasite could be harmful to humans. Who was In nineteen thirty eight there was a three day old newborn I was born at Baby's Hospital in New York City. She started having seizures and the doctors looked her all over and all they could see that was out of
the ordinary were these lesions in her eyes. Sadly, a month later she died, and so during the autopsy, doctors saw the same lesions all over her brain, and they wrote a case study up about this and this case study would end up being probably the first recognized case of congenital human toxoplasmosis because they found the parasites in her brain and then they injected it into animal models and then they developed encephalitis and so yeow, and so
at this point, Toxoplasma gandhia is a recognized pathogen, but there were still many mysteries surrounding the parasite, including the extent to which people were infected, like the prevalence, how they became infected, and many characteristics of the parasite itself, like its life cycle and its hosts. So researchers had detected the parasite and many different mammal species, but they
were unsure of which animal was the definitive host. So which yeah, And at first they suspected it had something to do with eating undercooked meat, which, as you said, it definitely does. And so in the nineteen sixties they these group of scientists designed an experiment in which they fed essentially raw lamb, like just barely cooked lamb chops to people with tuberculosis living at a sanatorium to see if they could transmit Toxicpasma gandhia.
I'm sorry, yeah, it is every episode this season is going to have some horrible experiment that we've done on humans.
Yeah. Well, in the experiment was successful, of course, because people they didn't kill people, but these people did become infected. But that didn't quite answer the question of what the definitive host was. It was just like, can you get it from uncooked meat. So a few years after this experiment, a parasitologist decided kind of on a whim to check out whether his cats had the parasite bingo. They did, and it didn't take long for other labs to confirm
these findings. And then this is like in the early nineteen seventies, and the backlash was there was like a strong backlash against cats. Apparently, according to one of the articles I read, there was like a lot of people and I don't know where exactly or how many killed cats out of fear thinking these cats are killing my children, these cats are killing you know, through this parasite. But I think for the most part, that was not the
common response. I think it did happen, but I don't think it was the common response because cat ownership has only continued to increase since that study was released. So after finding that felines are the definitive host for toxo. A lot more of the pieces began to fall into place, so the complex life cycle of the parasite was figured out, and people started to get an idea of how it causes these behavioral changes in rodents that influence the parasite's transmission.
So cool, it's so cool. And it's these early studies on the influence on the behavioral influence of rodents that really opened up this huge field of research about behavioral manipulation of parasites and what that might mean for humans and our micros. So I'll get to that in a bit. But that's basically the written history of toxo.
Wow, so short.
It didn't cause any massive pandemics or overtly changed the course of history in some dramatic fashion, and it isn't even old enough to have any like bizarre cures associated with it. It just basically consists of a series of scientific developments and findings. But there is more to talk so than that.
Yeah, like where did it come from?
Exactly? So remember how the parasite was discovered simultaneously at two different points on opposite sides of the world. Yeah, so there's a certain amount of coincidence that goes into that, but really what it tells us is just how incredibly widespread this parasite already was.
Yeah, like that wasn't new at that time.
That wasn't new. So the question is how did it get to be like that? And the answer is domestic cats. That truly is the answer. So I mean, yeah, let's go back in time. Let's go back to around eleven
thousand years ago. So it's around then when we see the very first evidence of agricultural societies, so people actually settling, keeping livestock, growing grains and plants at home, and we see this happen in different places all around the world over the next several thousand years, So in the Fertile Crescent is where it began, then in China, then Mexico,
in Western Africa, and so on. So around like eleven thousand years to go to four thousand years ago is when like the biggest you know, movement or shifts started to happen. And I've talked on this podcast before about how the formation of agricultural societies and farming, how that would have impacted disease transmission and what types of diseases were transmitted and what they would look like. So you know,
just a refresher. Larger human settlements means more transmission between humans, So you get these crowd diseases like tuberculosis and influenza, and then you also get zonotic diseases transmitted between humans and their livestock or humans and domestic animals. Yeah, and the human animal contact increases not just because of people choosing to own cattle or whatever other livestock, but also because of keeping large stores of grain and other food.
And then you get other little animals finding you.
Like mice and rats, et cetera.
Exactly. For example, how mouse. So there's archaeological evidence of the increase of the house mouse as human settlement increased, human agricultural settlement increases. So, twelve thousand years ago, the proportion of house mice bones found among small mammals near hunter gatherer communities was about five percent. But within a thousand years, which is like a long time but also a very short time, that number jumped up to eighty percent.
So like, of all the animals that they found near, like eighty percent of them were house mouse.
House Yeah, house mouses way to go wild.
Yeah, that's a huge change in one thousand years.
That's a mauge change. Yeah, so it's probably a good thing, or at least no surprise that cats were domesticated in the Fertile Crescent around the same time that agricultural societies began to there eleven thousand ish years ago, because.
There's so many mice for them to eat.
Yeah, it's probably not coincidental. Yeah no, But anyway, so there was a little cat named the near Eastern wild cat, who, even like the wild populations today, seemed to be very bold and not very aggressive towards humans. Are fearful, which is kind of interesting and makes sense. So these these types of cats came up to human dwellings and they made themselves at home, and probably in a way that's familiar to a lot of cat owners today.
It's like, Hi, I'm here, now, I will live here.
And so this caused a major shift in the dominant transmission pattern of Toxoplasma gandia. The sylvatic cycle, which is the natural cycle in the forests basically or in the wild wildcats, is exactly this is the one that still seems to be quite active in many places today. So this involves the wild felids and wild rodents, while the domestic cycle is the one that we are more familiar with and it's the one that has led to the
huge prevalence of toxo around the world today. This is one that involves our housecats and house mice, and scientists have looked at the genetic diversity of toxo around the world and have found that in urban areas where the domestic cycle dominates, there's less diversity because there's more mixing of the parasite populations, and that's in contrast with the higher diversity seen in places where the sylvatic cycle is more common, such as the forests of Central and South America.
But overall, the domestic cycle is the more common one, and the simple answer for that is housecats. So felines are the only animals that can serve as a definitive host, as you said, and wild felines have never really been at high enough population densities around the world to be able to result in the widespread and extremely high prevalence of toxo in humans. In humans, yes, in humans, yeah, but also in places where wild cats do not occur, we still see a ton of toso yeah in wildlife.
Right, Yeah, I'm not surprised about that.
And that is largely due to house cats as well. Why were cats domesticated in the first.
Place to eat them mice?
So that's probably part of it. So I read this book that's called The Lion in Your Living Room and it talks all about like it's all about the history of the cat. It's very fun and she is a huge lover of cats, and she's like, you know, it just doesn't really make a lot of sense. Like, dogs have tons of different roles, they have tons of jobs they can do. They're protective, they can work their useful. Cats you know, they can kill rodents, but for the
most part, cats soaken dogs. Yeah, and dogs are actually more effective at actually lowering populations of rodents because because there can be task oriented, whereas cats aren't as task oriented. So they've shown like studies that cats don't often actually effectively reduce rodent populations unless food, other food is extremely scarce.
Interesting because they'll.
Go for the low hanging fruit. That just makes more sense.
Lazy kitties.
This is like, this is famously captured in a video of cats scavenging for trash right next to rats, because they're like, I don't want to waste my energy killing and eating a rat when I can just eat trash. I mean, it makes sense you can blame them, and certainly now they do little to affect urban rodent populations, right so she did, though. So the author of this book, though, did started a file apparently called uses for cats when
she was researching this book. And I just want to list a few of these because they crack me up.
Please.
So, first of all, there was to encourage rain, people in Indonesia would parade cats around their fields.
Parade cats. I love it.
I wonder if parading cats is easier than hurtings that.
I mean, it's probably equivalent.
People use cat skin for musical instruments a lot. Oh. Apparently people in China used to use the cats dilating pupils to estimate the time of day, and they were also a critical part of many types of European tortures.
Ooh wow, So.
I'm quoting directly from her book. Medieval murderers were sometimes burned in a sack with twelve cats to maximize suffering, and during a punishment called cat hauling, a cat was dragged by its tail down the length of an offender's body.
Oh.
My god. Yeah, I feel so bad for the cats.
I know. Okay, So then there's some more modern things. So cat hair has been used in DNA evidence for murder trials, okay, which is pretty cool. Yeah. So anyway, those were a few of the things on the uses for cats list. But I mean, regardless of of their questionable skills as rodent controllers or any of these other powers, humans kept them around. And that's maybe putting it mildly. There's archaeological evidence of the love that humans have for cats.
There's a ninety five hundred year old gray for a kitten on the island of Cyprus. Baby m h. There's of course ancient Egyptian artwork, yeah, showing house cats. Worship of cats didn't.
Weren't cats to ward off evil spirits and stuff? They're like protectors of they were.
And then on the flip side of that, things weren't always so good between cats and humans. So I talked a little bit about it during the plague, but also cats in general in a lot of during sometimes in a lot of places were thought to be demons or agents of Satan. And some historians think that this might be due to the fact that allergies to cats are
fairly high. So like if a cat jumps on you and goes around your face and stuff, and then you all of a sudden your throat itches and you can't breathe, I mean, I would probably think, yes, this cat is like an agent of Satan. Anyway, wherever humans went, they brought cats with them, maybe as mouse or rat killers, or maybe just as a good luck charm. And cats, of course, were especially valued on ships, and sometimes sailors would refuse to get on a ship if it was
missing its resident cat. But when humans and cats traveled the globe together, there was this other hitchhiker that tagged along Toxoplasma GANDHII. And the proof of how far cats have traveled is in the global distribution of toxo. Toxoplasma gandhia is now found all over the globe, even above the Arctic Circle. Whoa, yeah, and in there it's not its way into beluga whales and other Arctic dwellers, and
it's like, OK, quite a problem. Yeah, And it's not just that where you find cats, you can find toxo. Thanks to water, Toxo can travel incredibly far and over the past one hundred years or even fifty years, cats have grown incredibly in popularity. People have moved into apartments in cities, cat litter was invented, and globally now there are around six hundred million domestic cats.
That's not as many as I expected.
Well, there are around anywhere from six hundred million to one billion cats worldwide. Okay, okay, And these aren't just pets. These are also feral cats, right right. And every day in the US more cats are born than there are lions in the wild.
Whoa, Yeah, that is a shocking statistic.
Yeah, and these cats aren't always pets. In Australia, for every one pet cat that has a home, there are six feral ones.
That's bad.
It's really really, really really bad.
Yeah.
And in the US only about sixty percent of the American pet cat population are kept indoors.
Ooh, that's bad.
Yes, that's really bad.
We touched on this in the Kittrid episode, but I assume we're going to talk a bit more about how important it is to keep cats indoors.
Yeah, so it's not I mean, it's not just that cats have single handedly wiped out entire species, many different species, but even Researchers have shown that even just their presence alone causes many problems, such as increased stress, making it difficult for some prese species to breed or parent properly. And they also spread disease feline leukemia, toxoplasmosis. And for the most part, these problems can be greatly diminished or completely fixed by keeping cats indoors. Cats have a huge
cascading effect on the ecosystem. And then when you throw in talcso it's a pretty big conservation and public health problem outdoor cats. And this is not easy to talk about, no at all, because people love their cats, and they love cats in general, and they can feel defensive about this. And by and large, if you have a cat and keep it indoors, you're not part of the problem. Your cat's not part of the problem. Strays and feral cats are much more problematic, and finding a solution that works
has not been easy. Yeah, And in this book, the line in the Living Room, she goes into this in a lot more detail. But there's this. You know, a lot of cities practice TNR, which is trap now to release programs, and people who are opposed to that point out that these cats are still outside, they're still releasing toso and they're still killing birds and endangered reptiles and mammals.
It's interesting because I hadn't I mean, I knew how big of a problem cats were for wildlife and things, and trap neudle release for cats that, like you know, are not going to get a home if you try and adopt them out.
Because they're they're feral cats.
Like they're not going to tolerate or or no one would want to adopt them. It's like, oh yeah, trap neudle release, at least they're not going to be making more cats. But then when you think about when I started reading about toxo and just how much of an impact a single cat can have, like, oh man, it's it's rough.
It's really rough. And you know, trap noodle release is meant to reduce the population of feral cats. It does not work because you would have to like if if your goal was simply to reduce population of feral and stray cats, trap noodle release doesn't work, Like there are just it's too effortful for the number of cats that you actually can capture.
There's too many cats out there that aren't being captured.
Yes, so but you know, euthanasia doesn't work either. Estimates suggest that if you that only if ninety seven percent of all feral cats in an area are euthanized, will population numbers actually go down permanently. WHOA, cats are very effective at the breeding like rabbits. I guess wow. And so this debate continues to go on over which practice is better or which practice is more humane. But the conversation is starting to shift a little bit because people
are realizing maybe it's not this versus this cats. We just have to accept that cats are part of the environment. So what do we do about it? That's maybe the more pressing issue, And that's not something that I'm going to attempt to answer. I just simply kind of wanted to bring this up because I think it's a really important bit of information about the problem of outdoor cats, and I think it's an interesting example of how conservation, public health, and animal rights can all be at odds
with one another. Yeah, there's no easy answer. There's no easy solution here.
Well, at least you can keep your own cat indoors.
That's an easy solution.
Yes, yeah, Okay, So you talked about some of the negative effects of toxow in humans, but toxo also can really devastate other animals, sometimes leading to or often leading to fatal infections. So this is the case, for example, with kangaroos. Kangaroos, Oh yeah, it's a big problem with kangaroos. It's also the case for sea otters, which I know is your favorite animal.
I know, it's toxoin. Seaotters is so sad.
It's so sad. And the fatal outcome in sea otters isn't necessarily just the direct effects of the parasite, but also the behavior alteration. So we know that toxic can affect the behavior of rodents infected with the parasite, and we've hinted at the subtle behavioral effects on humans. But it turns out that sea otters that are infected with toxo are three times more likely than their uninfected counterparts to be killed by a great white shark.
WHOA.
That is really fascinating because I was also reading that it's probably an underestimate how many otters die from toxo too, just because we only see the ones that wash up on shore, and not all of them obviously wash up on shore, and things.
And the prevalence is like something like thirty six to forty something percent some populations. Yeah, which brings me to the possible effects of toxo on humans.
Yeah, let's talk about it.
Oh, toxo on humans is very interesting and sort of it's both a budding field and controversial. Yes, there have been many different studies that that have tried to associate toxoplasmosis infection with increased risk of car accidents, suicidal tendencies, just overall attitude of personality changes, and the results are like, there are some compelling results, but a lot of them seem a bit difficult to disentangle, like not everything has been controlled, and it's like a very it just hinting
that there might be something going on there, not enough to I think say this is conclusively showing an effect.
Definitely, don't have any solid right, But.
The big one that has made the rounds is the association with schizophrenia. So basically, what proponents of this hypothesis believe or suggest that infection with toxoplasmosis leads to an
increased risk of being diagnosed with schizophrenia. So let's go through some of the evidence and support of this one thing that a lot of people say, or that a lot of people point to, is that there don't seem to be descriptions of schizophrenia prior to the eighteen hundreds, and that's sort of when cat ownership really came into fashion.
There's also the seasonality of schizophrenia, so people diagnosed with schizophrenia tend to be born in winter and early spring, which means that during the time their mom was pregnant, an outdoor cat might be spending more time indoors. But I also don't know if they looked at people from both hemispheres, yeah, if they controlled for that, and then whether it's like latitude alone, yeah, okay. Another piece of compelling evidence is that people with toxo and this is
sort of like the bottom line evidence. People with toxo are three times more likely than uninfected people to be diagnosed with schizophrenia.
Okay, But at the.
Same time, the vast, vast majority of people with toxoplasmosis have not been diagnosed with schizophrenia, and there are people who have schizophrenia who have been diagnosed with schizophrenia and do not have toxo, so so so then they suggest
maybe it's more of a predisposition or susceptibility thing. Yeah, and also compellingly, the some antipsychotic medicines that are used for people who have been diagnosed with schizophrenia do seem to be effective in stopping the progress of at least one stage of the parasite.
I think that that is very very interesting, yes, but does not mean that toxo causes no.
Yeah, let's look at the other side of the evidence, because this has gotten a lot of popular science press, and I think it just is like weighing the evidence is important. Yes, Okay, So there are huge geographic differences in toxoplasmosis prevalence, and some countries have prevalence rates of ninety percent and other are others are much lower, like
ten percent, twenty percent, which is still really high. But anyway, but the corresponding rates of skins it's to ania diagnoses don't match with these.
Okay.
So the place is where you find the most toxo. You don't necessarily find higher rates of schizophrenia diagnoses, and even looking within a country, you don't see a drop in schizophrenia diagnoses following a drop in toxo due to increased food hygiene standards or something. And the other thing is that these are all correlation studies. Yeah, so we don't know what came first? Was it toxo or schizophrenia?
Could it be that someone who has been diagnosed with schizophrenia is more likely to get toxo than someone who is not. Like, you know, these are correlation studies, and so some researchers have criticized these tenetive links between toxo and schizophrenia as building false hope. Once the public, though, got wind of the possibility that infection with this parasite could alter human behavior, the headlines have gotten just a bit more bizarre, and some of them pretty cringe or
eye rolling. Yeah, there's an opinion piece suggested that the Brazilian soccer team was so good because high rates of infection led to increased risk taking and aggression.
Oh my gracious.
Yeah so or maybe toxo did shape civilization itself. Who knows, you know. I wanted to talk a little bit about these studies, but mostly to say grain of salt this so I think I'm ready to get back onto some solid ground with real numbers. Can we please, Aaron, tell me where we stand with toxic today?
Oh?
You want me to do that, I do.
Okay, we'll take one more quick break, all right, So toxoplasmosis today, Like we said already, but it bears repeating. The estimated prevalence in humans of Toxoplasma GANDHII infection is between twenty five and thirty percent of all humans.
Twenty five and thirty percent of.
All of humanity. But like you mentioned, this isn't equitably divided in some places, where, for example, consumption of raw meat is more common, or in tropical areas that are very favorable for that oocyst persistence in the environment. In those areas, seripovolence can be as high as fifty seventy five or even ninety percent in some areas, and in other areas.
It's a lot lower.
In the US, it's estimated around twenty two percent, okay, and zero prevalence tends to increase with age, which makes sense because it's kind of just like you're living your life and at some point you'll be exposed. So the older people are, the more time they've had to be exposed. But these infections really do have pretty serious consequences. In the US, it's estimated that the annual cost I know you don't like looking at the numbers, but I mean the dollar numbers.
Oh No, I mean I think it's important. I think it's just important to keep in mind also that the US cost is going to be very different than other places that have better health services for their population.
For sure. But in the US it's estimated that the cost of illness is three billion dollars and eleven thousand quality adjusted life years lost.
Wow.
Also, did you know that over two thousand people develop eye disease from toxoplasma in the US every year? But and here is something I absolutely did not realize. Toxoplasma GANDHII is one of the three Salmonella, Listeria and tea GANDII. These three pathogens account for over seventy five percent of all deaths due to food born illness in.
The whoa yeah, whoa right.
It's estimated that toxoplasma in two thousand and eleven, I believe, caused eight percent of hospitalizations and twenty four percent of deaths from food born illness.
So why don't we hear about this more?
Why don't we hear about this?
We hear about this?
You know, bananas tenuous at best. Links with schizophrenia, and we don't hear about people dying from toxoplasma infected meat.
Or cold food. Are these associated with particular Is this like an outbreak or are these.
Individual cases individual cases, so we don't really probably.
Explains why they're not as headline worthy for sure. For sure, for sure.
Yeah.
Now that's in humans. It's not only in humans, it's not only in mice and rats, and it's not only in cats. Over three hundred species of animal can be infected that we know of with Tea gondii. Hugely important is the fact that because these oss persist in the environment, they can get into the soils and the water and end up like you mentioned in our oceans. Did you know that in Moro Bay alone is in northern California by the way, Yeah, okay, in Morbay alone, domestic cats
deposited seventy seven tons of poop. That's not including free roaming cats, which deposited another thirty tons of poop. That means forty five hundred little parasites osis per square meter.
It's really hard to even fathom.
Yep, because these cats, so infection in cats is generally asymptomatic. Cats are the definitive host for the parasite. The parasite doesn't cause illness in cats very often at all, but cats shed this parasite for up to three weeks at a time when they get infected, and they're shedding thousands and thousands of these parasites every time they poop. It really does have a huge impact on wildlife and other animal populations across the globe.
It's a pretty big conservation and public health problem.
Yeah, So one of the things that's really interesting is that there's a big push to look at toxoplasmosis from a one health perspective, which we've talked very briefly about one health on this podcast before, but essentially one health is just this idea that animal health, wildlife, domestic animal
and environmental health all play into each other. So looking at disease from all of these different aspects and trying to get a handle on understanding the risks of disease from an interdisciplinary perspective is really important for control, not just for humans, but for the entirety of wildlife, domestic animals,
and the environment. So for toxoplasmosis, that means trying to get a better handle on the risks from the environmental perspective, so soil studies land use effects also a better understanding of the potential effects on human behavior tenuous though.
They may be.
Understanding the extent of congenital transmission. It's estimated that there are anywhere from four hundred to four thousand cases of congenital toxoplasmosis in the US alone every year.
Wow. And that's it. And we have a relatively low prevalence rate. Yeah we did other countries.
Yeah, we really do.
And is this is not a reportable illness? Is congenital toxo reportable?
It is not a nationally reportable disease? Wow, which means we don't really have a good handle. That's why the estimates are anywhere from four hundred to four thousand cases.
Makes sense? Yeah, yess.
But then also understanding.
The wildlife and domestic animal cycles.
Food safety is.
Really important in talking about toxin plasmosis. And then like you mentioned, outdoor cat monitoring and control efforts and of course vaccine development. There is actually a vaccine for sheep that's licensed in some countries. Yeah, but there isn't even a vaccine for cats, which is kind of bonkers to me.
There was one that was made at some point, but it was very expensive to produce, it was difficult to keep, it had a very short shelf life, and cat owners didn't care about it, probably because it doesn't generally affect cats negatively, so it was discontinued by the manufacturers.
Huh.
Yeah, interesting, So that sucks.
Yeah, it does seem that sort of The biggest ways that you're likely to be infected are from contaminated meat sources, so cooking your meat properly is important. But also the osis can persist in the environment, so contaminated water is.
A huge issue.
The osis actually are viable. They're not killed by chemical and physical treatments that we use for water treatment, including chlorination and ozone treatment.
Yeah, and they can.
Survive freezing and pretty high water temperatures, so cool cool. Yeah, so toxic is pretty much everywhere. Again, the vast majority of humans who get infected will never ever know that they were infected, but for people who are imm compromised or for pregnant people who get infected the first time, the effects can be very devastating.
Yeah, it kind of remains this vague threat that, Yeah, it does.
And then for wildlife species it can be really damaging as well, So it's a really happy ending toxic is pretty fish.
Yeah, Aaron, tell us about your sources.
I read a couple of books. One I already mentioned called The Line in the living Room by Abigail Tucker. This is a very fun read. I recommend it. And then another book by Catherine McAuliffe called This Is Your Brain on parasites and that's another fundread as well. And then I read a bunch of different articles, mostly by JP Dubey. Oh he's like I read. I think I saw some of Yeah, tons and tons of he runs troll research.
Yeah.
Yeah. And one of the books, yeah, And where I got all the information or a lot of the information about sort of the human evolution and agricultural settlements was from a paper by schwab at All from twenty eighteen.
It was great, awesome.
We'll post all of our sources for this episode and all of our episodes on our website, this podcast will Kill You dot Com under the episode's tab.
Thank you to Bloodmobile for providing the music for this episode in all of our episodes.
Thank you all for listening and for keeping your cats indoors safely with you and with that wash your hands, you filthy animals,