Cat parasite may give you the crazy

For many years, Jaroslav Flegr, a biologist at Pregue's Charles University, suspected that a parasite in cat feces, the same ones that can harm a pregnant woman's fetus, can actually screw up the mind of anyone who comes into contact with it. Turns out, he may be right. From Kathleen McAuliffe's excellent article in The Atlantic:
 ~Flegr Ctvrtky Prednasejici Flegr (According to Flegr,) the “latent” parasite may be quietly tweaking the connections between our neurons, changing our response to frightening situations, our trust in others, how outgoing we are, and even our preference for certain scents. And that’s not all. He also believes that the organism contributes to car crashes, suicides, and mental disorders such as schizophrenia. When you add up all the different ways it can harm us, says Flegr, “Toxoplasma might even kill as many people as malaria, or at least a million people a year.”

An evolutionary biologist at Charles University in Prague, Flegr has pursued this theory for decades in relative obscurity. Because he struggles with English and is not much of a conversationalist even in his native tongue, he rarely travels to scientific conferences. That “may be one of the reasons my theory is not better known,” he says. And, he believes, his views may invite deep-seated opposition. “There is strong psychological resistance to the possibility that human behavior can be influenced by some stupid parasite,” he says. “Nobody likes to feel like a puppet. Reviewers [of my scientific papers] may have been offended.” Another more obvious reason for resistance, of course, is that Flegr’s notions sound an awful lot like fringe science, right up there with UFO sightings and claims of dolphins telepathically communicating with humans.

But after years of being ignored or discounted, Flegr is starting to gain respectability. Psychedelic as his claims may sound, many researchers, including such big names in neuroscience as Stanford’s Robert Sapolsky, think he could well be onto something. Flegr’s “studies are well conducted, and I can see no reason to doubt them,” Sapolsky tells me. Indeed, recent findings from Sapolsky’s lab and British groups suggest that the parasite is capable of extraordinary shenanigans. T. gondii, reports Sapolsky, can turn a rat’s strong innate aversion to cats into an attraction, luring it into the jaws of its No. 1 predator. Even more amazing is how it does this: the organism rewires circuits in parts of the brain that deal with such primal emotions as fear, anxiety, and sexual arousal. “Overall,” says Sapolsky, “this is wild, bizarre neurobiology.”

"How Your Cat Is Making You Crazy"



    1. The article immediately made me think of crazy cat ladies. I thought they had thirty cats because they were crazy, but maybe I’m confusing cause and effect! 

      1. Compared with uninfected people of the same sex, infected men were more likely to wear rumpled old clothes; infected women tended to be more meticulously attired, many showing up for the study in expensive, designer-brand clothing.  

        Ah, never mind.

  1. The smell of our cats’ feces is enough to drive me crazy.  Mr. Shibi refuses to scoop the poop so it’s all on me.  So to speak.

  2. How is this news?  Everyone knows cats are parasites that are capable of “extraordinary shenanigans” and making people “feel like a puppet”!  

  3. If you read to the end of the article, the chances of going crazy from cats is very small.  If your cat is an outdoor cat, there is a small 3 month period after they start hunting when they can infect you with T Gondii.  You should be more concerned with eating red meat then having a cat as a pet.  BTW, the personality effect only shows up under statistical analysis, it is incredibly small change, most certainly not a primary cause of the crazies.

  4. I’m sold on his beliefs. One of my favorite books of all time is “Parasite Rex’ by Carl Zimmer. He eloquently describes in great detail the motivations of wide range of  parasites including Toxoplasma and he echoes many of Flegr’s theories. Zimmer’s book is a fascinating look at how the millions of parasites that live amongst us have evolved into spectacularly refined organisms. He left me with the understanding that many parasites are to be feared, but even more so, respected.

  5. As the interNet is made of cats, it would seem that the parasites are also stimulants to the sort  of technological obsessions which made it possible.

  6. This seems like a good example of why extraordinary claims only require ordinary evidence.  Anything else is just an excuse for clinging to old beliefs.

  7. This is obviously junk science meant to panic people into not letting their cats sleep on their chest at night. Jaroslav probably works with the dog lobby.



    1. Sorry guys, I guess my cat was on the keyboard. I’ll give her some treats, freshen her water, clean her litter, play with her favourite string, and then gently but not too gently pet her belly until she’s ready for more cat treats.

      I’m not sure it would matter if I was brainwashed.

  8. This is interesting, since I’ve long assumed that I carry toxoplasmosis, and furthermore, a lot of people do.  It isn’t that rare, Wikipedia says over half the world’s human population is estimated to carry it, and in the US, they say probably 10-11% of people.  I know it makes rats act somewhat foolhardy in the presence of cats, and I’ve even heard that it can be linked to risk taking behavior in people, but if it affects as many as 1 in 10 people, doesn’t that constitute “normal”?

  9. This is hardly news.  Toxoplasmosis has been known to be a central nervous system infectious agent for a long time and cat poop the vector.  See TORCH Complex (the T stands for toxoplasmosis).  

    While most articles talks about pregnant women and their fetuses, within medical circles it’s also known to apply to non-pregnant women and yes, even men.

    ransom notes, agree with you about Zimmer’s book.

    1. Yeah, I didn’t know it was controversial… the question is the frequency of acute infection versus “benign.”

      It does make me kind of hypochondriac about changing the cat litter, holding my breath while scooping, to the point of dizziness.

      Which, of course, is likely to eventually lead to me passing out face down in the litter box. In fact, given the cosmic humor that seems to control events in my life, surely that’s how I’ll be found after a sudden, lethal aneurysm.

    2.  I’d agree that it’s not exactly new, I’ve been hearing about Toxoplasmosis studies since I was an undergrad. (~6 years ago) Though the wording of the theory was…odd. As far as I remember it, a study back then found men with an outbreak of Gondii were “More aggressive and antisocial” and thus “less attractive to women” while women were “more outgoing and prone to sexual experimentation and promiscuity” which made them “more attractive to men”. You don’t say?

      Anyway, there’s theories that between as much as one to two thirds of mankind may be infected with latent toxoplasmosis, so just as the human papillomavirus, it’s probably too late to stop it anyway, if we ever could have stopped it. And as the article stated, there’s plenty of other parasites which might just be influencing us anyway. Given how many symbiotic liveforms inhabit the average human colon alone, humans are not individuals, they are collectives, microbiologically speaking.

      In short, it is something that is fascinating to discuss, but pretty much out of our reach to influence if it is true. But it does crop up on the internet every other year and makes dog owners feel smug about themselves until it submerses itself in the gloom of lesser-known scientific pursuits again. But if it one day lets us devise treatments for clinical anxiety, why not, it’s not like it can break out of a lab and infect us all, because it already has.

    3. My understanding was that it doesn’t affect people with functioning immune systems, that the blood-brain barrier basically kept it out.  

  10. I think this is the third time this topic has come up on boing boing…? “Cat Parasites Control Our Lives”

    Radio Lab has an excellent episode on Parasites. Chase it with the episode on Choice to disabuse yourself of the fantasy of free will. :)

  11. Last I heard, parasitologists were largely behind the idea that they probably have some effect on human hosts..

  12. He may be a genius but only his hairdresser knows for sure. Looks like he’s got some parasitic action going on up there.

  13. We have had a conversation, and we have come to a decision. 
    Now that you know of our existence, we shall have to silence you.

  14. What the hell has no one else noticed how much this guy looks like Larry Fine from the Three Stooges?  It looks like Moe could walk in the room at any minute & slap the guy for his scientific audacity.

  15. I’ve always wondered if there was a connection between owning primarily indoor female cats, toxoplamosis, and infertility in women. Of the women I know, it was just weird to me that those who had trouble conceiving or were diagnosed as infertile from unknown cause, most of them (including myself) owned primarily indoor female cats. Those women who were able to conceive seemed to have more premature deliveries, and miscarriages, as well as fibroids more often than those whose pet ownership status didn’t fall into the same category.  It didn’t seem to be the case with owners of male cats (my own difficulties seemed to start when my male cat died and I adopted two female cats) or with dog owners of any type.

    Of course, given the number of pet owners in my circle of freinds and acquaintances, all of this can probably be explained away, which is why I only asked about it once when talking to my doctor ( who looked at me, understandably, with some amusement before answering that there was definitely no connection).  Still, this can’t help be make me wonder how much we don’t know. 

  16. This may explain why I now sleep in a basket while my kitty Brian spends all day on my bed watching porn and smoking weed.

  17. next post:

    18 tigers, 17 lions, 3 cougars  “They had split before he actually went to prison,” says Huntsman. “He had accused her of turning him in for the guns. How could you blame a woman you have spent forty years of your life with for that, if you were sane? He was just going off the deep end. Terry became so verbally abusive to Marian. He didn’t trust anybody after that. He didn’t even trust his own wife.”
    “He had a heart of gold. He just couldn’t keep his brain on the right track.”

  18. I have seen the effect of  Lyme Disease on people and have observed personality changes and changes in behavior falling in the mild crazy category.  The theory is an interesting one since we know parasites need environments that are habitable and the changes in habit and personality may produce a better evolutionary advantage for the parasite.

    1. Besides the possible nerve problems with Lyme, try living with chronic pain and/or incapacitating weakness for a long while – which I believe are major symptoms of Lyme disease – and see what it does to your personality and behavior.  When my arthritis pain was at its worst, I think I went through some periods when I was pretty hard to live with or work with.  There’s a good reason the adjective “maddening” is often attached to chronic pain.

      1.  I know many people diagnosed and several of them have talked about changes to their personality beyond the physical effects of the disease.  The psychological changes can be just as crushing. A husband of someone infected said that his wife had no physiological effects, they were, as near as anyone can separate the mind and body, all psychological.
         In the public sphere the author Amy Tan has talked about those effects.

      2. My Lyme disease was primarily annoying, and the cure was far more debilitating than the disease, but I diagnosed mine fairly quickly.

        Mrs. Kagehisa is completely asymptomatic, although she’s apparently had Lyme disease for years.  She’s half done treatment, so far so good.

        One of our neighbors had crippling nervous pain, though, from his Lyme infection.  It seems to be highly variable in its effects.

  19. I had thought this was a fairly commonly known idea. I remember hearing about it as a child (early 80’s) and assumed it was why I liked jumping out of perfectly good airplanes with only  a nylon bag strapped to my back.

  20. I think I’ve been rewired to accept my cats wire chewing, shedding, and knocking things over and taught to only focus on the cute stuff. 

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