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When executive producer Ellen Horne was expecting a baby, she really had no particular intention of becoming a self-made expert on a parasite named Toxoplasma gondii. Robert Sapolsky explains to us why Ellen had reason to worry when she was scratched by her cat, and he traces the unlikely path that the parasite might follow, right up to the point that it rewires a rat's brain. Fuller Torrey details Toxoplasma's potential associations with other human disorders, possibly even schizophrenia.

Comments [34]

Feral cats are vermin that most communities will not deal with. That bad samaritan on the block who feed cats should ask his neighbors if they want to own one? Because honestly, they don't just stick in the yard of the feeder, they are all over the neighborhood.

This article underlines the risk of having outdoor cats living in your neighborhood. Keep your housepet cat indoors and pressure your community to rid your area of feral cats.

Sep. 08 2016 10:10 AM
William Davis from Nausea, New Hamster

Yet more Junk Radio from RadioLab! …and another reason why I refuse to send any money to NHPR!!! CLICK!!!

Sep. 05 2016 07:59 PM
Rebecca from Los Angeles

I listened to this in the car yesterday and was crushed by the incomplete and misleading information about cats, transmission, and prevention. I work in rescue here in LA and every year hundreds of cats end up abandoned at shelters (where their outcome is not good) because their humans became pregnant. If cats are kept indoors, there is very little likelihood of them being infected. If there is a concerned that a pet is infected, get them tested by the vet. It is treatable. Anyone who is pregnant and owns a cat, should get this test if they are at all worried.

Cats should be kept indoors. They are an invasive species and damage what remaining struggling ecosystems we have in our urban and suburban settings. (The odd feral or stray here and there, that cannot be kept in a home needs to be sterilized.) Being outside is dangerous for cats, they can be hit by cars or killed by predators. Further, cats can contract parasites and disease by going outdoors -- as Moose likely did.

I was surprised that Moose was not tested for toxoplasmosis and that the affects of that parasite on a cat was never explored in the show. Interestingly, diarrhea, something that Moose apparently suffers from, is a symptom of toxoplasmosis infection. There are other, more serious symptoms as well.

Cats have enough to overcome without misinformation like this.


Sep. 05 2016 12:22 PM
Delusionalmyass from San jose

I am chronically bothered by this parasite-have been for more than five years in the fall and winter of each year. I am intensely allergic and must remain on antipsychotics and allergy medicine. I am sure that I was infected by my cats-I love gardening and my cats like to be outside too and hang out with me as I garden. I always wear gloves now but it's too late. Also, there are lots of mice and my cats constantly brought me "presents" of the mice they caught and ate the guts before leaving me the carcasses. Anyway, I fear they will be the death of me-it is almost impossible to kill them and they go dormant when it's too hot or dry. My stuff-bed, clothes carpets have .ived through at least 5 cycles themselves (years) and have multiplied and gotten stronger each generation-they are truly like living with a devil.!! They have wrecked such havoc in my life and They are winning Anti-parasitics. my body makes too much dopamine and that's why they are so attracted to me. The antipsychotic I take, along with an antidepressant are supposed to lower my dopamine or that is what I was told. Thearasite had this long to take over because my family, doctors, employers, friends EVERYBODY except one true friend,do not nor have they ever believed there is a deadly parasite haunting, bothering, causing me pain and energy and hope~and I've fought so hard, for so long and and I think I'm just a little ahead of you all-this parasite, as well as many others, have just begun to inhabit our world-I just feel exhausted If anyone out there can relate I'd sure like to hear. Thanks and God bless......

Feb. 07 2015 12:44 AM
an c from San Francisco

My mother had toxoplasmosis during her pregnancy. She had it from eating vegetables that were not properly washed -- some cat had unfortunately relieved itself on the greens my mom ate. It was very scary for her but fortunately we both survived it. Anybody know what long-term health issues could arise for either mom or baby (no adult)?

Nov. 18 2014 05:18 PM

I've had cats all my life and I have never been made sick by them. I change their litter regularly and I make sure I wipe all my counters and the kitchen table daily. Two of mine currently like to go outside. They are older cats, as my youngest of the five that I own are 6 years old. To me, they are a better pet than any dog would ever be and I'm keeping them.. All this fuss when all you have to do is keep from inhaling or ingesting fecal matter.. geeze..

Oct. 19 2014 06:53 AM
Susan Waage

As a veterinarian, I have to inform clients about the risk of Toxoplasmosis. I am appalled at the misinformation presented in your story. Please inform your listeners that they are more at risk of Toxoplasmosis from eating undercooked meat or digging in their gardens than they are from their pet cats.
The test that your producer took was a test for antibodies to Toxoplasma; therefore, it only indicates previous exposure and immunity to the organism. It does NOT indicate that she is actually infected with the parasite.
Here is a link to the CDC web page with accurate information regarding Toxoplasma:

Oct. 12 2014 02:13 PM

I (like Meredith above) had also read that toxo is excreted in young, outdoor cats' feces for a limited amount of time. The source was the excellent article in The Atlantic, also cited by Josh O. above. Here is the link to it, again, followed by a quotation from it

"GIVEN ALL THE nasty science swirling around this parasite, is it time for cat lovers to switch their allegiance to other animals?

Even Flegr would advise against that. Indoor cats pose no threat, he says, because they don’t carry the parasite. As for outdoor cats, they shed the parasite for only three weeks of their life, typically when they’re young and have just begun hunting. During that brief period, Flegr simply recommends taking care to keep kitchen counters and tables wiped clean. (He practices what he preaches: he and his wife have two school-age children, and two outdoor cats that have free roam of their home.) Much more important for preventing exposure, he says, is to scrub vegetables thoroughly and avoid drinking water that has not been properly purified, especially in the developing world, where infection rates can reach 95 percent in some places. Also, he advises eating meat on the well-done side—or, if that’s not to your taste, freezing it before cooking, to kill the cysts."

Oct. 12 2014 02:49 AM

Robert Sapolsky blows my mind every time I listen to him. I'm following his class called Human Behavioral Biology on Youtube.

Dec. 15 2013 03:29 PM
Leon Li

My bio prof recommended this to our neuroscience class- just wanted to say this is a well-composed podcast! Engaging. Rich aural textures and also rich storyline.

Nov. 24 2013 02:26 PM
danielle from seattle

Please put all the recordings of the cat purring together and sell them to me!

They were amazing.

Jul. 24 2013 03:40 AM

Four weeks ago I saw Kevin Slavin deliver an Ignite talk (at Walker Art Center, MN; part of EYEO Festival) about this very topic. My reaction upon watching it was "this guy is just making up this stuff." After listening to this Radiolab segment, his talk appears to be at least somewhat evidence based. It's quite wacky, but masterfully delivered and entertaining. A worthy 5-minute watch:

Jul. 22 2013 10:29 PM

Yet another in the long list or reasons I would never have a cat. They are cute and fun, but to me they come with too many risk factors t be a practical pet.

Jul. 21 2013 02:25 PM

Given that domesticated cats were worshipped and even mummified in Ancient Egypt, I find it hard to believe that there is a link between schizophrenia and cats from the 19th century.

Jan. 07 2013 02:27 PM

I found this story entertaining but very incomplete, full of speculation.

First of all, toxoplasmosis can't be spresd to humans from a cat scratch. It has to be ingested. It's an oral-fecal infection (which means the infectious oocysts that spread the disease have to get in your mouth)so good hygine, thouroughly cooking meat, and washing vegetables is the best defense. Also, cats can only shed the oocysts (which are the way that the disease spreads)for about 2 weeks after they become infected.

About 40% of the worlds population is infected with toxoplasmosis. Most people are infected from undercooked meat or poorly washed vegetables because the oocysts are present in most soil. If a woman is infected with toxoplasmosis prior to becoming pregnant her baby is not affected. The danger is only if a woman contracts the infection for the first time during (or immediately before) pregnancy.

The incidence of car accidents in infected people is most likely due to slowed reaction times (a documented concequence of toxoplasmosis infection) and not recklessness or fearlessness caused by the parasite.

And lastly, the schitzophrenia conection mentioned that correlates the domestication of cats in the mid 1800's and the "development" of schitzophrenia is likely to be due to the fact that schitzophrenia was considered to be demon possession prior to that time- as were all other forms of mental illness? Presently, drug companies are looking for a link between toxoplasmosis and schitzophrenia in some people due to the parasites ability to disturb normal dopamine production. Seeing that about 40% of the population is infected- it seems unlikely that toxoplasmosis causes schitzophrenia in everyone.

Aug. 19 2012 10:15 PM
Josh O. from Chicago

Did you guys see this article in The Atlantic?
More sinister reaching possibilities for how this parasite could be rewiring human brains. Maybe the crazy cat lady is really a zombie?

Feb. 10 2012 04:28 PM
Jesse-who-has-toxo from NYC

Incredible Radiolab episode. I had one thought on the connection between toxo and car crashes. It can wind up in people's eyes and affect vision (blurriness, milkiness, floaters, blind spots). As it heals, it leaves a scar, but also sometimes a permanent blind spot in one eye. When the other eye's vision overlaps, it corrects, and you don't notice the blind spot. Maybe the car crashes were related to toxo's effect on people's vision.

Nov. 27 2011 10:33 PM

I don't think toxo would "control" our behavior, especially concerning emotion... it would more like alter the way we process and produce emotional behavior and responses. It's either going to change the way electrical signals are transferred or create lesions in that area of the brain, which changes the way those signals are fired and received. I don't believe there's any parasite out there responsible for mind control, it's more like mind alteration.

Oct. 22 2011 03:46 PM
Levi Bates

I'm am writing a report about schizophrania, and this really helped me out. However, I was wondering if you had a list of sources writen out so I don't have to skip around through the podcast again. You probably do somewhere,
I'm just not seeing it.


Feb. 22 2011 01:33 PM
Beth from Cuyahoga Falls, Ohio

I recently listened to this story, and was wondering how executive producer Ellen Horne and her baby are doing? An update would be fantastic....I've found she keeps popping up in my mind (sadly, it's usually when I'm cleaning out the litter box! Not a great association, I'm afraid), and am hoping she and her baby are well.

Apr. 08 2010 08:17 PM

If Toxoplasma makes you like cats, I am definitely infected. And I've wondered about this: To me and other cat lovers I asked, cats don't really have a scent. Sure, the litterbox smells and if you use perfumed litter your cat smells like that. But when I stick my nose in cat fur, I don't smell anything. All other animals I can think of have a pretty specific scent (goats, anyone?), including dogs and hamsters, also kept as pets. Did toxoplasma affect my senses in a similar way to rodents?

To uninfected people, or people afraid of cats, do cats smell?

Mar. 06 2010 11:12 PM
David P Williams from Canada

Fight Toxoplasmosis, Swallow This

Cat genes promoted
t, gondii
changing behavior
of prey.
As scat fed mice
seek out cat odors
while disinclined
to run away

Tabby's charming gift
to women
testosterone terror
in men
for women, compulsion
to nurture
for men, compulsion
to win

An entire nation
where infestation
is high.
Patriarchy becomes
under repression
her heart
must die
The man is trapped
as surely.
A warrior and
a thrain
honor driven,
vendetta ridden
all due to the worm
in the brain

Whole sects and religions
are founded
on secretions of
the worm.
Brain's Godspot
by the feline's
odious germs

No wonder the Egyptians
enthroned the cat.

So influential
was he.
(Asleep on Momets sleeve)
He conjured women's
and men's sad destiny

I am here as a representative of the Canadian Association of Toxoplasmosis Sufferers or C.A.T.S.
Toxoplasmosis is a parasitic (T.Gondii) infestation transmitted from cats to mice and to humans, through feline scat (feces). Its acute noticeable effects are light flu symptoms lasting briefly. However, the secretions of the parasite continue chronically to effect the brain, long after the infestation ends completely. In mice it drives out fear of cats and actually makes cat odor attractive to rodents.
In humans it effects male and female brains differentially. Accentuating "womanly deference and nurturing qualities" and male testosterone fueled dominance and aggression.

Remember! Stay away from kitty litter, and don't rub cats the wrong way

DAVID P WILLIAMS (902) 454 9564 April 2004

Feb. 28 2010 03:32 PM
Alice from Minneapolis, MN

I am very interested in the link between Toxoplasma infection and schizophrenia being my mother has schizophrenia and my sister and I both have seizures. I think I will be looking into this further out of pure curiosity. Anyone with any information or comments along this topic, please feel free to post back. Love to hear 'em...

Feb. 27 2010 12:11 AM
Seeol Briinger from Norrath, Virginia

"The Scratch" was a very interesting show. I saw a similiar story from Doctor Kefalonia from Greece regarding this very subject. I wonder what other parasites control us humans!!!

Jan. 15 2010 02:41 PM
Ann from Naperrville, IL

"The Scratch" was fascinating!!! Thanks!

Jan. 06 2010 02:51 PM

The Sapolsky lecture here

Dec. 21 2009 06:14 PM
Jon from Denver, Co

Kelsey Smith?
Kelsey Grammar!

Nov. 05 2009 10:53 AM
Corey from Portland, OR

Moral of the story: don't eat cat poop.

Oct. 22 2009 04:40 PM
Digital Man from DC

Great show on "The Scratch"

Kelsey Smith from St. Louis needs to be slapped;)

Oct. 07 2009 11:42 PM
Tentaculistic from Arlington, VA

This was such a horribly (by which I really mean wonderfully) fascinating story. The parasite rewires the rat's brain that it becomes aroused by the smell of a cat, its hardwired enemy?? Oh wow that is just so deeply twisted, and of course the sci-fi novel ideas just lep off the mind from there...

Oct. 05 2009 03:29 PM
Jon Alexandr

Or maybe not. The link seems to work correctly now.

Sep. 25 2009 02:29 AM
Jon Alexandr

"The Scratch" mp3 is a duplicate of "In Defense of Cheats." I wanted the segment about cats.

Sep. 25 2009 01:08 AM
barry from pdx

i hope the person who left the previous comment is trying to be funny, my lord!

Sep. 19 2009 05:55 PM
Kelsey Smith from St. Louis

Do you have editors that sift through your material before it's posted? I just noticed a mistake that might affect a viewer's outlook on your articles, and how reputable your information might be if the grammar is incorrect. "becoming an self-made expert" should be "a" instead of "an".

Sep. 11 2009 03:00 AM

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