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Medicine Science

Cat Parasite May Increase Risk of Suicide In Humans 252

An anonymous reader writes "Researchers at the University of Maryland analyzing meticulous data collected by Danish authorities have identified a positive correlation between suicides among women with infection with the fairly common parasite T. gondii. Carriers were 53 percent more likely to commit suicide in a sample of 45,000 Danish women monitored for over a decade (researchers believe that the same correlation likely exists for men). Increased susceptibility to schizophrenia and bipolar disorder was also discovered. The physiological mechanism has not been determined, although some speculation centers around changes to dopamine levels. Two intriguing aspects were noted: 1) human infection often (but not always) begins by exposure to cats carrying the parasite, for example, by changing an infected animal's litter; and 2) the parasite spreads itself by infecting the nervous system of rodents, causing them to become suicidally attracted to feline odors which will increase the likelihood of their hosts being eaten by cats, whose digestive tracts provide the preferred environment for parasite reproduction."
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Cat Parasite May Increase Risk of Suicide In Humans

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  • by jeffb (2.718) ( 1189693 ) on Sunday July 08, 2012 @05:19PM (#40585305)

    ...but it's still okay to eat cats, right? I mean, as long as you avoid the digestive organs?

  • by pyzondar ( 1234980 ) on Sunday July 08, 2012 @05:20PM (#40585315)
    Do the crazy cat ladies have cats because they are crazy, or are they crazy because they have cats?
    • Re: (Score:2, Funny)

      by Anonymous Coward

      Either way this explains Caturday.

    • by girlintraining ( 1395911 ) on Sunday July 08, 2012 @05:43PM (#40585511)

      Do the crazy cat ladies have cats because they are crazy, or are they crazy because they have cats?

      The parasite also causes decreased sexual inhibition. Translation: It makes women sluttier. No corresponding effect was found in men. Of course, this effect isn't as widely documented for obvious political reasons...

    • by toygeek ( 473120 )


    • by Anonymous Coward on Sunday July 08, 2012 @06:03PM (#40585655)

      If you knew anything about these parasites, you would not write what you just did.

      Cats are carriers. Rodents are part of their life cycle. Rodents infected with these parasites tend to be "more brave", some even to the point of taunting a cat to attack them. The cat eats infected rodents, and the cycle of the parasite is complete as it returns to the soil and rodents pick it up once more.

      Humans are just unintended side show for the parasite, but since these affect behaviour in mice brains, it is not surprising these parasites affect human brains too.

      http://www.livescience.com/5631-zombie-ants-controlled-fungus.html [livescience.com]

      Is another example of similar effects in non-mammals by other, yet similarly acting organisms.

      In a similar unrelated note, there are experiments that show even more bizarre behaviours, like effectively a "personality transplant" by a swap of gut bacteria cultures between two mice. One aggressive and another docile. Swap their gut cultures, and you swap their bahaviours!

      There is plenty of other research starting to appear in this area,
            http://www.sciencedaily.com/releases/2011/05/110517110315.htm [sciencedaily.com]

      So basically, how you eat may tell what you are/may become and your becteria and viruses play bigger part in your life than you can image.

      • by stephanruby ( 542433 ) on Sunday July 08, 2012 @07:42PM (#40586397)

        You seem to know about this field. Can you translate this part for me?

        Separate logistic regression for RhD-negative subjects showed a 2.53 times higher risk of traffic accidents in Toxoplasma-infected than Toxoplasma-free subjects (CI95: 1.12–5.7, t = 2.23, P = 0.026). http://www.biomedcentral.com/1471-2334/9/72 [biomedcentral.com]

        Are they really saying that this is causing "2.53 times higher risk of traffic accidents" among their infected population of Czech male military draftees???

        Imagine the repercussions if this is found to be also true in other populations (not that it will be, and not that correlation equals causation, but...):

        Car Insurance rates (or driver licenses) could start depending on the results of those blood tests. Criminal sentencing could be affected by the results of those tests. And at the very minimum, the next time you'd fill out a questionnaire for getting car insurance, or filling out an application for becoming a truck driver or operating heavy machinery, or applying to get into the military, you'd be asked all kinds of questions about your history with cats (whether you owned one, your significant other owned one, or whether your family ever owned one while you were growing up).

      • This topic was covered in a segment of RadioLab [radiolab.org] a few years back.
    • by couchslug ( 175151 ) on Sunday July 08, 2012 @06:05PM (#40585671)

      "Do the crazy cat ladies have cats because they are crazy, or are they crazy because they have cats?"


    • by ChunderDownunder ( 709234 ) on Sunday July 08, 2012 @08:53PM (#40586941)
      Crazy or just plain HOT? You decide [youtube.com] :)
  • Which came first? Crazy cat lady got 20 cats because she is crazy, or cat lady went crazy because she has 20 cats?
    • Maybe the lady got one cat, got infected, went crazy, and got 19 more? (Remember, the parasite causes rodents to be attracted to cats; maybe it has a similar effect in humans.)

      • Humans don't need parasites to be attracted to cats. Kittens work for that purpose just fine.

  • by Anonymous Coward on Sunday July 08, 2012 @05:22PM (#40585337)

    sure, this looks like valid research, until you see the citations

    Resurch dun by Carnegie Meloncat Institute fellows:
    with speshul thx 2 cieling cat hoo make all tings possible

  • Kill all cats. (Score:5, Insightful)

    by SuricouRaven ( 1897204 ) on Sunday July 08, 2012 @05:27PM (#40585381)
    They are a menace to public health.

    That's what people would say if cats were ugly, anyway. But they are cute, so they are permitted to carry disease. Only ugly species are eligable for culling.
    • Well, they also help defend against the Plague by killing the carriers.

    • Re: (Score:3, Insightful)

      by Anonymous Coward

      It has been my experience that without exception people that think of cats that way tend to be serial killers or have the potential to be serial killers anyway.

    • They are a menace to public health. That's what people would say if cats were ugly, anyway. But they are cute, so they are permitted to carry disease. Only ugly species are eligable for culling.

      All animals carry diseases, including human beings. Maybe we should sterilise the Earth, and leave a nice clean Lunar environment.

  • The Origin? (Score:5, Funny)

    by Insanity Defense ( 1232008 ) on Sunday July 08, 2012 @05:33PM (#40585433)
    The first stage in the evolution of the Gou'ald has begun.
  • by InterGuru ( 50986 ) <jhd AT interguru DOT com> on Sunday July 08, 2012 @05:35PM (#40585447) Homepage

    The purpose of the behavioral change in rats is to get the rat gobbled up by a cat so that the parasite could reproduce. I wonder if toxoplasmosis in humans promotes reckless and suicidal behavior. This would give the parasite another opportunity to reproduce. Just imagine 50,000 years ago a suicidal or reckless person decided to taunt a hungry tiger. One strike by the annoyed tiger, and the toxoplasmosis would have access to a warm cat gut to reproduce. Isn't nature wonderful

  • and no one has offed themselves in my house. Maybe smoking dope counteracts the parasite :)

  • by jamesh ( 87723 ) on Sunday July 08, 2012 @05:42PM (#40585499)

    Once the cats perfect this virus it's all over...

  • So, I mean like, does this mean if you have, like, a liger, cleaning his cat box will, like, blow up the whole, like, neighborhood? Or maybe, like, the parasites will, like eat my face? Gosh. Idiots! I'm sure. http://en.wikipedia.org/wiki/Liger [wikipedia.org]
  • by changing an infected animal's litter

    Now I know that they are not going to be the same between men and women. A woman is likely to change their litter box more than once a year; which is what a man will do.

    • What I do is the cat lives outside. But as a gadget lover, what I would do if I had an indoor cat is get a snazzy litterbox. And if the cat crapped on the rug in protest of the shit machine I'd swap it out for another cat. Maybe show the new cat a picture of the old cat going away...

      • There's a better way - toilet-train the furballs instead. I have two cats whom I, after much hair-pulling, successfully trained to use a regular toilet. It's also a lot cheaper and more sanitary, and stinks less too. One flush and their leavings are dealt with. No litter box to clean also means no more of a risk of diseases than one encounters from regularly cleaning a toilet used only by humans in the first place. Note that the smarter the cat and the more time and patience you can muster, the faster

  • by Dr_Barnowl ( 709838 ) on Sunday July 08, 2012 @05:52PM (#40585573)

    Also evidence of correlation with religion ; a higher incidence [nih.gov] than average amongst Muslims and Christians (a shame this study didn't assay Atheists though).

  • I was sure I have read that on Cracked.com years ago. Can't seem to find it now :(
  • by AK Marc ( 707885 ) on Sunday July 08, 2012 @05:59PM (#40585629)
    A 50% increase is statistically significant, but in absolute numbers wouldn't make that much of a difference, certainly well under the "killed by cars" number, and we don't care enough about that to actually fix the problem.

    What I see out of this, and others like it, is that there are a large number of diseases we get infected with over our lives that never leave us, and have effects well into our old age. We wouldn't have "evolved" out of them because the evolutionary pressure for things that don't affect us until after we've passed on our genes is small and indirect. How many "diseases" and infections do we have by the time we are die? What would our old age be like if we managed to avoid/cure them all?
    • It affects risk management, increasing risk-taking behaviour, so part of that "killed by cars" number could also be attributed to T.Gondii...in fact I remember reading about other studies that have explicitly linked (or tried to link) the two.
      • by AK Marc ( 707885 )

        It affects risk management, increasing risk-taking behaviour,

        If true, what do you think would be appropriate steps to take? It seems to me to be more a dog-based conspiracy. Some mythical "cat-spread" disease that's incurable that causes unknown undesirable effects.

    • by Hatta ( 162192 )

      A 50% increase is statistically significant

      No, you don't know whether it's statistically significant unless you know the uncertainty in the measurement. A 50% increase with a standard deviation of 100% would not be statistically significant. A 1% increase with a standard deviation of .1% would be statistically significant. And that's all without considering sample size.

  • I'm no PhD, but I'm perplexed.

    FTFS: "causing them to become suicidally attracted to feline odors"
    That just seems like a really high-level cognitive function for single-celled organism to achieve in a mammal.

    I guess I can see it affecting dopamine levels, but causing an attraction to a specific odor?
    Can anyone explain?

    • by tomhath ( 637240 )
      Natural selection happens.
    • A relatively simple method would be a feedback loop. The parasite could stimulate dopamine receptors whenever it is exposed to compounds linked to feline odor. Since the parasite is already in the nervous system, it would be pretty easy for it to be hanging around the blood-brain barrier or the nasal system to receive the odors first hand even.

      Ever see the dumb shit people will do coked up? Now reduce the cognitive inhibitions to the level of a rodent. Chemically, it's all the same.

  • Of course, my evidence consists of multiple repeated viewings of Tom and Jerry, Sylvester and Tweety, and Pinky and the Brain, but according to my research, it's exposure to Mince and Rats that creates suicidal tendencies in Cats.

    Just saying.


  • Shit i have 2 cats...

    FUCK EM!

  • by Harvey Manfrenjenson ( 1610637 ) on Sunday July 08, 2012 @07:26PM (#40586279)

    The Danish study is just the latest in a long series of studies which demonstrate a correlation between toxoplasmosis seropositivity and psychiatric problems-- it's been linked to schizophrenia and ADHD, and so on. Wikipedia has a good article on the topic.

    It's pretty interesting. Apparently something like 10% of the US population is seropositive for toxo. The infection is thought to be "contained" immunologically, but encysted organisms are still present in muscle and nervous tissue, and the process of "containment" may induce a subtle inflammatory state which affects a broad variety of neurotransmitters (not just dopamine). It's also possible that the causation works the other way-- the people who get chronic infections may have something about their immune system that is different to begin with, and the difference might predispose them to psychiatric problems independently of toxo infection. Good discussion of all that in the Danish study, which was published in Archives of General Psych and seems to be non-paywalled.

    What will be really interesting is to see what happens if you identify psychiatric patients with chronic toxo and try to eradicate the toxo with antibiotics-- do their psych symptoms improve? There have been at least two studies I could find (one where it helped and one where it didn't), and apparently there's a large-scale study getting started in the UK.

  • by ivi ( 126837 ) on Sunday July 08, 2012 @07:34PM (#40586329)

    Subj says it all. Others may have noticed the same.

    Could those in the extra 53% suicidal women have suffered earlier miscarriages, by any chance?

    • by Mashiki ( 184564 )

      I also seem to remember that the same parasite can cause a whole host of problem in a developing fetus too.

  • Control group (Score:5, Interesting)

    by phantomfive ( 622387 ) on Sunday July 08, 2012 @07:35PM (#40586341) Journal
    For people who are wondering, it looks like they didn't have a good control group. So here is how they answered some potential objections:

    1) What if depressed people get cats, and that's why they have the parasite? Did they check people who have cats but aren't depressed?
    It's probably not related to cats, because most people who get this parasite get it from undercooked meat.

    2) What if depressed people are more susceptible to this parasite because they are depressed? What if non-depressed people are capable of fighting off the parasite with a stronger immune system?
    There was no correlation between people who had the parasite, and people who had a history of mental illness. (Also, correlates with other studies, that might have had better control groups, I'm too lazy to check them out to see).
  • It was popular in the 1970's, you can go to the doctor and get the cure.... ;-)

    • only 1% later self-harmed

      Thanks, I was looking for that number. That's quite significant with 45k people.

  • ...watching you go crazy.
  • I can't help thinking that I've heard this before some years ago. Am I right or is this really a new finding?

Life in the state of nature is solitary, poor, nasty, brutish, and short. - Thomas Hobbes, Leviathan