Culture Dish

A lot of people probably look at the video I’ve posted below and think, Awh, it’s a hilarious rat who just loves his friend the cat! But when I watch it, I can’t help imagining something evolutionarily larger.

Some background information: The parasite Toxoplasma infects many species (including an estimated 60 million people in the US), but it can only undergo sexual reproduction in cat digestive tracts. Evolutionarily speaking, this means toxo’s survival depends 100% on its host being eaten by a cat (even if its host is human; more on that below the jump). So toxo has evolved a complicated system for taking over its hosts’ brains to increase the likelihood that they’ll be eaten by cats (for example: it rewires rat brains so they’re actually attracted to the smell of cat urine). Knowing this, I ask you: Is this rat just friends with this cat? Or is it actually in a toxo induced frenzy and trying to get eaten? If so, then this video is an example of a cat kicking toxo’s ass (to a hilarious soundtrack):

If all cats were like this one, toxo would eventually cease to exist.

Now, on a more human note …

Last year, I wrote an article questioning whether all of this might explain the ubiquitous Crazy Cat Lady syndrome: Maybe their obsessive cat collecting is actually a sign that toxo has taken over their brains and is making them hoard cats to increase the likelihood that they’ll be eaten by one. So far, no one has studied that theory.

Thanks for the video link, Meg, though your peeps may not want to think about this one ;-).

[Update: Those entertained by the idea of a toxo infected rat desperately trying to get eaten by a cat should check out my pal Scott Westerfield’s book Peeps, which features a such a toxo-infected rat (plus vampires and other fun things).]


  1. #1 jabfish
    January 5, 2009

    ooh. I completely agree with your toxo-CCL syndrome hypothesis. The CCLs must either carry some resistance to toxo or get infected by a less virulent strain of the bug to explain their long life spans.

  2. #2 Dave
    January 5, 2009

    Your cat lady hypothesis could be tested relatively straightforwardly, I think. First you would have to come up with a clinical definition of ‘cat-lady syndrome’ sufficient to decide unambiguously whether or not someone was a ‘cat lady’ or not. Then you need to get the brains of these cat ladies, along with brains from age & lifestyle-matched controls. Then you check for toxoplasmosis cysts in the brains of both groups. The null hypothesis is that cat ladies and control ladies will have the same incidence and severity of toxoplasmosis infection.

    If cat ladies tend to be more infected (e.g. p for the results in the experiment above turns out to be less than 0.05), then the next step is to test whether anti-toxo drugs bring them back to their senses.

    Easy peasy. For a million dollars, I’ll work on it for ya. Or (more likely) subcontract the study. I don’t want to have to write the human experimentation protocols.

  3. #3 christopher guerra
    January 6, 2009

    i was just wondering if the toxo parasite like to live in humans or does it get stuck there on accident?

  4. #4 Bob O'H
    January 6, 2009

    Dave – you’d also need to infect some women to see if they turn into cat ladies. That could be a fun application to write to the ethics board.

  5. #5 Frasque
    January 6, 2009

    That was YOUR theory? Then do you know you inspired a YA book titled “Peeps” by Scott Westerfield? in the book the Toxo-type parasite turns people into vampires (sort of) but cats form an important link in the whole chain.

  6. #6 Ward S. Denker
    January 6, 2009

    Knowing this, I ask you: Is this rat just friends with this cat? Or is it actually in a toxo induced frenzy and trying to get eaten?

    As someone that’s had kept many rats as pets over the years, I can say that the former is a real possibility.

    The rats in the video probably been socialized with people (and the cat) since birth. The more socialization they get with humans and other animals the less timid they become. They’ll do things no (uninfected) wild rat will do, like chase other animals and play with them like they play with one another.

    Those are some cute little guys in the video!

  7. #7 Ed Yong
    January 6, 2009

    You can get some toxo of your own:

    More seriously, Kevin Lafferty’s done work on the effects that Toxo has on human behaviour on an international scale. Obviously, very controversial, but REALLY interesting.

  8. #8 Pat McComb
    January 6, 2009

    Thanks for posting this. My cat, Al, was playing with a mouse recently. Al has killed mice before, but would not kill this mouse. In fact, the mouse made no effort to escape. After a game of tag, the two of them just stared at each other. I wondered if this was adaptive on the cat’s behalf — don’t eat any critters that are too easy a catch.

    I’ve wondered about Crazy Cat Lady syndrome and toxo also. I’d heard that toxo has been (albeit anecdotally) linked to other behavioral changes in humans and may even create symptoms similar to schizophrenia.

    I’m surprised a thoroughgoing study of toxo in humans hasn’t happened yet.

  9. #9 Rebecca Skloot
    January 6, 2009
  10. #10 Frasque
    January 6, 2009

    Maybe I’m misremembering, but I thought the infection was passed directly from cats, and while it didn’t cause hoarding it did make the victims really over-concerned about the health and welfare of the cats . . . of course, real toxo doesn’t turn people into vampires, either. *shrug*

  11. #11 Pierce R. Butler
    January 6, 2009

    Is Crazy Cat Collector Syndrome also observed in human males?

  12. #12 Skloot
    January 6, 2009

    EdY! I’ll buy you MRSA if you buy me Toxo …

    @Pierce: Yes, actually, it is seen in men (though not as commonly). Also not limited to cats

  13. #13 Maureen Lycaon
    January 7, 2009

    Er, Frasque: Crazy Cat Collectors (people who hoard literally dozens of dogs or cats without regard to their ability to care for them) usually aren’t concerned at all with the pets’ welfare. Ask any Humane Society or animal-shelter workers who’ve had to deal with them when the problem finally went to the health department or the police.

  14. #14 Rebecca Skloot
    January 7, 2009

    Yep, Frasque, toxo is spread directly from cats, which is why cats loving rodents would be a big problem for toxo. In order for toxo to reproduce then infect other species, it has to be inside a cat first. It can (and does) live just fine in any species, Christopher, it just can’t reproduce in any but cats for some reason.

  15. #15 Dave
    January 7, 2009

    It should be mentioned that most cases of toxoplasma infection are not directly from cats, but from eating undercooked meat of intermediate hosts or from (presumably accidental) ingestion of cysts in the soil.

    So they may be cat ladies now, but they probably got that way from not washing their hands after gardening.

  16. #16 Rebecca Skloot
    January 7, 2009

    Frasque and others curious: Scott Westerfield’s book Peeps is totally related to all of this. I mistyped above when I said the toxo in his story didn’t come from cats … of course, all toxo comes from cats at some point, since that’s where it reproduces. I meant that his character who was running around trying to spread toxo wasn’t a cat. It was, in fact, a rat … … you can learn more here (hi Scott!).

  17. #17 MattK
    January 7, 2009

    Problem with the non-experimental protocol: hoarding cats may cause toxoplasmosis since it obviously provides greater opportunity for infection. Guess we’ll have to go experimental.

    Toxoplasma was what killed the one of the characters in Train Spotting (but he had AIDS and so was immunocompromised). Toxoplasma can also be very dangerous to human fetuses if their mothers newly acquire an infection while pregnant.

  18. #18 Laurent
    January 8, 2009

    It is apparently frequent that cats won’t hunt animals that belong to their ‘nesting’ territory. I’m told for years even if I always find it difficult to believe. My partner’s cat never killed any mice that happened to move onto the boat, despite she was a quite famous hunter on the shore. To the great deception of the other boat inhabitants (but the rodents).

  19. #19 Laurent
    January 8, 2009

    Otherwise, toxo contamination from rodents to cats can happen in other ways than prey eating, so I’m not sure this would be the end of toxo at all.

  20. #20 catharine
    January 8, 2009

    I learn more medicine from the internet than I ever did in medical school

  21. #21 Maija Karala
    January 9, 2009

    The “hugs and kisses” the rat gives to the cat on the video don’t look like normal behavior – but that’s exactly what my pet rats do to me and almost all other people they happen to meet. They are not exactly scared of small dogs either, so I think they would probably like a cat as much.
    I’d say the rats’ behavior is completely normal, but I’m not that sure about the cat.

  22. #22 Maija Karala
    January 9, 2009

    The “hugs and kisses” the rat gives to the cat on the video don’t look like normal behavior – but that’s exactly what my pet rats do to me and almost all other people they happen to meet. They are not exactly scared of small dogs either, so I think they would probably like a cat as much.
    I’d say the rats’ behavior is completely normal, but I’m not that sure about the cat.

  23. #23 alayna
    January 9, 2009

    On the lighter side, as a lesbian, could any of you scientifically explain why I have noticed it is mostly gay women I have known that posses this problem :) Perhaps 5 or 6 cats doesn’t officially qualify as crazy cat lady syndrome to some, but that looks toxo crazy to me!

  24. #24 tim
    January 13, 2009

    One problem with your hypothesis about toxoplasma and CCL syndrome is that a very large fraction of the population is infected with toxoplasma. You are probably infected, even if you live in a developed country like the US. I don’t have a reference, but once looked into this and read a whole bunch of stuff about toxoplasma, and in developed countries some huge number like %40 of humans are infected by age 12. I don’t see why the infection rate would go down a whole lot as you get older, so the adult population must have a very high infection rate, though I remember reading that it is not very well known what it is.

    Toxoplasma is one of the most common and successful orgarisms around, and is very common in the soil (as one type of cyst that resists cooking and water) and also meat, especially pork. You can find studies that investigate how common it is in various types of meat.

    Even pre-cooked ham is still sometimes infectious. It’s easy to vaccinate against, though, and it is easy to destroy in meat with gamma treatment. People should have the option of getting vaccinated if they want to. The infection can also be cured. Personally I would like to be cured….. If I had the money I might look into it :-(. It wouldn’t hurt.

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