2:05

Fending out nature, the noob must

2:08

stop and criticize one

2:10

human box at a time until

2:13

all mice lose

2:16

their fear of cats.

2:21

Here, baby kitty,

2:24

coming this Halloween to

2:26

the science podcast for

2:29

this, not so close but

2:32

the cat and mouse chase just

2:34

got more interesting.

2:44

Okay, so I

2:46

guess is toxoplasma gondii

2:48

coming this fall? Oh, it's

2:51

already here. So it's a little

2:53

parasite that infects mice and makes them

2:55

lose their fear of cats. Yes,

2:58

toxoplasma gondii

3:01

is the only way we're going to say it. I

3:03

see. So, and then I guess

3:05

being infected by the parasite makes the mice

3:07

easier to catch so then cats eat them more

3:10

and then I guess that something

3:12

with kitty litter. What's the play

3:14

here?

3:15

You've got the basic idea. But

3:18

like any trailer, it's only a teaser

3:21

of the full story. And

3:24

to tell our terrifying true

3:26

science tale, we have Sebastian

3:29

Loredo, a biologist

3:31

who studies toxoplasma gondii.

3:33

And he said he's willing to play

3:36

along

3:36

with our film project. If

3:39

you were to cast yourself in

3:41

this movie, what

3:42

role would you be playing? I'm

3:45

thinking of Jurassic Park.

3:48

I think I would be the cautionary scientist

3:51

who's saying like, are

3:53

you sure you were going to do that? Like

3:55

things don't always turn out the

3:57

way that we think about this.

3:59

Scientists are always saying that in

4:02

movies, and honestly also in real life. You

4:04

know, they're always the ones who turn out to be

4:07

right. Because they always

4:09

have the most uncertainty.

4:12

So, Sebastian is

4:14

on a mission to find this parasite's

4:17

weakness, so he can destroy

4:20

it.

4:20

And that's often

4:22

the case in the horror movies as well, right?

4:25

Where all of a sudden

4:27

you identify some unexpected

4:30

susceptibility in the alien

4:32

creature,

4:33

and that can be exploited to its

4:35

defeat.

4:37

Now, I can see the final scene now, the scientist

4:39

and the parasite face to face, or I guess

4:42

microscope to face to face. What

4:46

does a parasite even look like? Does it have a face?

4:51

And where do the mice and the cats and the kitty litter come in here? Yeah,

4:53

I

4:53

think we're getting ahead of ourselves,

4:56

so let's go back to the beginning and set

4:58

up exactly what we're dealing

5:00

with. Oh yeah, I mean we should probably

5:02

define what a parasite is first. Yes, let's do it.

5:07

At the most basic level, we're thinking

5:09

about organisms that really

5:11

depend or rely on other organisms

5:14

to survive. The

5:15

organism that a parasite needs

5:18

to survive is called a host. The

5:20

host provides food and a place for the

5:22

parasite to reproduce or make copies

5:25

of itself. Intoxoplasma

5:28

makes some cool-looking copies.

5:30

So the parasites

5:32

are kind of banana-shaped, or in some

5:35

cases a little bit more avocado-shaped. It

5:38

could look like a banana or a rounder banana.

5:40

That's probably not the scariest-looking

5:43

creature

5:43

you could imagine.

5:45

And it's just a single cell,

5:47

so it's really small, not

5:49

intimidating, but it's big

5:52

enough to see with a normal microscope.

5:55

And it's got some special

5:56

parts. That little banana

5:59

shape. And it's very sick.

6:01

Very, very specialized properties.

6:04

That tip is where the parasites

6:06

can release very sticky

6:09

substances that they use to stick

6:11

to our cells.

6:13

Oh, sticky banana. I've

6:15

touched those before.

6:18

This is more cunning than your average

6:21

banana.

6:21

I don't know. Banana's pretty cunning. And

6:24

they can actually move those sticky substances

6:27

down the length of the

6:29

banana, if you will, to allow

6:32

them to propel themselves forward.

6:34

This sticky banana motion

6:36

lets them act like a cellular

6:38

cat burglar, breaking into

6:41

cells with no one noticing.

6:43

They are actually moving throughout

6:45

our tissues and moving over our cells

6:48

and moving into our cells.

6:49

Once in the cells, they

6:51

make themselves at home and replicate.

6:54

All of a sudden, reach a point

6:57

where they start writhing and start

6:59

moving around and finally burst

7:01

out, looking for new host cells

7:05

to infect. And so it is

7:07

maybe like a microscopic version

7:10

of what

7:11

we know from a lot of horror

7:13

films.

7:15

OK, that's pretty terrible. So

7:17

that's how it looks like from the parasite's perspective.

7:20

But what does it look like from the outside?

7:23

If you zoom out from inside the body and

7:25

take the wide pan and just see a mouse and

7:27

a cat, what are they doing?

7:29

Nice film direction there. OK,

7:32

so the sun is shining. It's

7:34

a normal day outside

7:37

in a normal neighborhood anywhere

7:39

in the world.

7:40

And we see a cat on the hunt.

7:43

So if your cat is hunting out

7:46

birds in the wild or hunting

7:48

mice in the wild, it can actually contract

7:51

toxoplasma from eating those wild

7:53

animals. And then it can bring the toxoplasma

7:56

back into our home. Oh, no, the

7:58

cat's own nature.

7:59

has become an agent for a kind of evil.

8:03

There's so many layers to this, and that's

8:05

why the movie really works. Yeah, sure. But

8:07

yeah. Wild animals

8:10

can pick up Toxoplasma from

8:12

their own environment and carry

8:14

it. And Toxoplasma

8:17

wants to be carried

8:18

straight into a cat. The bear

8:21

is at just feet and sees whether

8:23

that host that it's found itself

8:25

in is going to get eaten by a

8:27

cat or not. So it's sort of like getting

8:30

on the first bus that comes to your stop and just

8:32

kind of like hoping it takes you into the cat

8:34

intestines that you want to end up in eventually.

8:37

Toxoplasma does have a little

8:39

trick up its little banana sleeve

8:41

to sort of hijack the controls.

8:45

At least in mice, scientists have

8:47

seen that Toxoplasma can cause

8:49

a change in behavior.

8:52

It makes those mice

8:53

less willing to avoid cats. So

8:58

it's not just hopping on the bus. It's hopping on the bus,

9:00

kicking the driver out, and then driving it right

9:02

to a cat. Right.

9:04

It's like whispering in the

9:06

ear of the mouse, like don't

9:08

be afraid of that nice little kitty.

9:11

It wouldn't even hurt a fly.

9:13

Kitty is friend. Friend

9:16

is kitty. Yes, and scientists

9:18

know this because they've done experiments

9:21

to reenact this situation.

9:24

Yeah, in the experiments that have been documented,

9:27

mice have this innate fear

9:30

of the smell of cats and

9:32

very specifically the smell of

9:34

cat urine.

9:36

In the experiments, mice that aren't

9:38

infected with Toxoplasma stay

9:40

far away from the cat urine,

9:43

but mice carrying the parasite don't

9:46

seem to mind it. And

9:48

mice that are infected with Toxoplasma

9:51

seem to dampen that response, seem

9:53

to lose their aversion,

9:56

their fear of the cat smell.

9:58

That's kind of nuts that they're... can be a parasite

10:01

that can just infect you and make you want to love

10:03

the thing that wants to eat you. I

10:07

have kind of like a side question. Is

10:09

this why people love cats? Are they being mind

10:11

controlled by a parasite? Are they being

10:14

mind controlled by a parasite and it's only our

10:16

dumb luck that cats are too small to eat us?

10:19

That's a great question.

10:20

And we'll find out the answer

10:22

right after this short break.

10:30

Homo is brought to you with support from Spotify for

10:32

Podcasters. If you're so inspired

10:34

by me and Lindsay that you want to make a podcast of

10:36

your own, Spotify for Podcasters has

10:39

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10:45

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platforms. See? Easy.

10:57

If you're interested, just go to Spotify.com slash podcasters

11:00

or download the Spotify for Podcasters app. We're

11:02

back.

11:03

When we left off, we

11:05

were wondering if human cat lovers

11:07

are being mind controlled by a parasite

11:10

into loving cats. I'm

11:11

really curious to know this because it could really

11:13

explain a lot.

11:14

OK, I think you're talking about the

11:17

cat lady stereotype here.

11:19

I am. And I feel like

11:21

this is the moment to find out if there's scientific

11:23

validity to it. Are they forced to be

11:26

that way by a mind control parasite?

11:28

Sebastian

11:30

says that some scientists have

11:32

looked into this idea, but they

11:34

haven't made any real conclusions

11:37

because it's actually a

11:39

really hard question to study. Even

11:41

if there is an effect and you see

11:43

that cat ladies tend to be infected

11:46

with toxoplasma more often

11:48

than dog ladies, I don't know

11:50

what the control would be.

11:53

I really want to help design this experiment comparing

11:55

dog ladies to cat ladies. Me too. Which

11:59

is more infected?

13:59

can become infected and

14:01

then contract toxoplasma themselves.

14:04

Well that's pretty gross

14:07

just in case you needed another reason to be grossed

14:09

out by kitty litter. So

14:11

is it common for people to be infected

14:13

with toxoplasma? It is really

14:16

common. Here's the statistics

14:18

for the United States. The number

14:21

of people who've been infected tends to be around 10%,

14:24

one in ten people.

14:26

But then you go to places like where I grew

14:29

up in Colombia, so Cali

14:31

Colombia, South America,

14:34

there about 64% of people

14:36

are infected.

14:40

So your likelihood of getting toxoplasma

14:42

depends on where you live?

14:43

Yes, and that's because of

14:45

different behaviors.

14:47

Some countries have more

14:49

stray cats or some people might

14:52

eat more raw meat. That

14:53

might be infected and get

14:55

it directly without the cat intermediary.

14:58

Oh geez, that's kind

15:00

of pretty alarming. But what does toxoplasma

15:03

do to us beyond maybe

15:05

making irrational decisions in an animal

15:07

shelter?

15:07

Well first it infects our

15:10

own cells.

15:10

The things that these organisms

15:13

can do

15:14

to our cells are

15:16

unbelievable.

15:18

The fact that

15:19

these little organisms can burrow

15:22

into our cells

15:24

and somehow not kill them,

15:26

maintain them in their lively

15:29

state, and then start replicating

15:31

inside, creating more and more of

15:33

themselves, and finally burst

15:36

out. Sebastian

15:38

sounds kind of disturbingly excited about that.

15:41

I think it's like the moment in the movie where the main

15:43

character is like appreciating the genius

15:45

of his enemy. And just like wow,

15:48

you're so good at being evil. Kind

15:50

of got to admire it.

15:51

Those are incredible traits

15:54

from any perspective. Okay,

15:56

so but like what's the evil plan for human

15:58

domination?

15:59

There really isn't one.

16:02

Generally speaking, we are what

16:04

we call dead end hosts for Toxoplasma.

16:07

Oh, so we're like the end of the road for the parasite?

16:10

Yeah, its whole life revolves around

16:12

getting into more cats through cats

16:15

eating other animals.

16:16

Of course,

16:18

humans are rarely

16:20

eaten by the cat. Thankfully,

16:22

we're rarely eaten by our pets. I'm

16:25

so glad. So when Toxoplasma ends up in

16:27

a human, they're out of the

16:28

game. But

16:34

there are certain times in our lives

16:36

or like different situations when

16:39

Toxoplasma can be more dangerous

16:41

to people if we're infected.

16:44

They are an

16:45

important human pathogen. They make

16:47

some people very sick.

16:49

So the biggest period of risk for humans

16:52

is during pregnancy. Doctors

16:54

always tell their patients that cleaning

16:56

the kitty litter during pregnancy is

16:59

a big no-no. That's because

17:01

of Toxoplasmosis, the

17:03

illness that Toxoplasma causes.

17:06

And so that's sort of one situation where

17:08

it can have very bad consequences

17:11

for a developing baby. Like,

17:14

oh no, I guess you can't empty

17:16

out the cat box. That's really too

17:18

bad.

17:20

But it's a well justified excuse.

17:23

Otherwise, there's a few instances

17:25

when the parasite gets the opportunity

17:27

to spread. And that can make

17:30

you really sick. But for most

17:32

people who are infected, a healthy

17:34

immune system keeps Toxoplasma

17:36

in check.

17:37

And so the parasites themselves

17:40

would be so rare throughout

17:42

the body that you would not really be able

17:44

to detect them. Well, that's good news

17:47

and certainly for cat lovers who don't want to give up

17:49

kitty litter duty for some reason. So

17:52

what is Sebastian doing to fight them? Because

17:55

they seem like pretty formidable little

17:57

microscopic banana-shaped enemies.

17:59

Well, Sebastian is looking for treatments

18:02

for people who do get sick. And

18:05

he does that by learning as much

18:07

as he can about how toxoplasma

18:10

works. And we're starting

18:12

to understand, we're starting to put together

18:14

the clues, we're starting to see

18:16

what the weak spots are, which

18:19

are the processes that they depend

18:21

on. And that's what ultimately

18:23

gives us opportunities through understanding

18:27

to control them.

18:29

And then he can make medicines that

18:32

target those weak spots or

18:34

make vaccines that keep people from

18:36

getting infected in the first place.

18:38

And then at the end of the movie, or many,

18:41

many years, the scientist emerges victorious

18:43

over his nemesis through a period of peer

18:45

review. Well, Sebastian

18:48

has an edit to that ending.

18:50

The heroes in real

18:52

life are teams of people. They're

18:54

not individuals.

18:56

The true story is there's not

18:58

going to be one single scientist

19:01

or one moment of genius that

19:03

solves everything. Many

19:05

labs, including Sebastian, are

19:08

in the fight against

19:08

toxoplasma gondii for

19:11

the long haul. OK,

19:13

but so what do we do about this? Is there

19:15

a way to avoid this banana-shaped evil

19:17

doer?

19:17

Do we have to give up our pet cats?

19:22

All the giddies can stay.

19:23

Because like so many

19:26

sicknesses, your best line of

19:28

defense

19:28

is washing your hands really

19:30

well.

19:31

So if you take out the kitty litter,

19:34

wash your hands. Make sure that things

19:37

are being cleaned, particularly

19:39

when you're going to then prepare food. Yeah,

19:43

so the takeaway here is don't eat kitty

19:45

litter, which on

19:47

purpose or by accident.

19:50

It's like solid advice to me. Maybe

19:54

the end of the movie is more exciting. A

19:57

twist. It would never really.

19:59

a horror movie, it is just

20:02

part of life

20:02

and thus living in an ecosystem

20:05

with

20:05

parasites. And parasites aren't

20:07

evil geniuses, they're just

20:09

organisms that saw

20:11

a creative way to live.

20:13

So you're saying Toxoplasma isn't out to

20:15

get us. It's just like, I just want

20:17

some place to live and have babies. Exactly.

20:21

Parasites don't have

20:23

bad intentions. They just

20:25

are. We often

20:28

believe that there is no purpose, there

20:30

is just opportunity.

20:32

There is no purpose, just

20:35

opportunity for parasitism. Meow.

20:41

Now that you've heard our scary science movie trailer,

20:43

write and perform your own. Choose

20:45

something from nature or

20:46

science that seems like it could be

20:48

its own scary movie. Maybe

20:51

it's a spider catching an insect in its web, which

20:53

is definitely scary from the point of view of the insect.

20:57

Or a zombie fungus. Write

20:59

a short script for your

21:01

movie trailer, then record it. You

21:03

can do it with audio like us

21:05

or video. Or you could

21:07

even draw each scene from your trailer

21:10

like a comic book. If you make a scary

21:12

science movie trailer, we'd love to see it or hear

21:14

it. Share it with us at TumblePodcast at

21:16

gmail.com. Thanks

21:20

today to

21:21

Sebastian Lurido, Associate

21:23

Professor of Biology at the Massachusetts

21:26

Institute of Technology and a member

21:28

of the Whitehead Institute. Special

21:30

thanks to Amy Tremblay and Lisa Gerard

21:33

at the Whitehead Institute.

21:35

Want to learn more about Toxoplasma gondii?

21:37

Tune in to our interview with Sebastian on the bonus

21:39

episode on our Patreon at patreon.com

21:42

slash tumblepodcast. And we'll have

21:44

more free resources

21:45

to learn about Toxoplasma

21:47

and parasites on the blog on

21:50

our website at sciencepodcastforkids.com.

21:52

Sarah Roberson

21:54

Lentz edited this show and designed the

21:56

episode art. Elliot Hijaj is our production assistant and you can

21:58

find him on our website at sciencepodcast.com.

21:59

Gary Calhoun James, engineered and mixed

22:02

this episode. I'm Lindsay Pederson,

22:04

and I wrote this episode. And

22:06

I'm Marshall Escamilla, and I made all the music

22:08

and sound design bonuses. Tumble

22:10

is a production of Tumble Media. Thanks

22:13

for listening, and stay tuned for more stories

22:15

of S.E.A.D.S.

22:16

Super 8.