Toxoplasma: Cats, Rats and Mind Hacks

Toxoplasma: Cats, Rats and Mind Hacks

Bizarre and Beautiful: More than a third of the world’s population is infected with the parasite Toxoplasma gondii. We pick it up from uncooked meat or from changing a cat’s litter box. Although apparently harmless to healthy adults, “Toxo” is dangerous to the human fetus and to immuno-compromised people. This is why pregnant women and people with vulnerable immune systems are advised to avoid cats.

Mind Control: The parasite infects the limbic areas of the brain near the fear and sexual attraction regions. Because it carries a gene that codes for an enzyme crucial in dopamine production, it can alter levels of this neurotransmitter. Infected rats become oddly fearless of cats but not of anything else, making it likely that they end up in a cat’s intestine, the only place where the parasite can reproduce! They also make more testosterone and mate more, ensuring the spread of the parasite to other rats. The ability of parasites to manipulate host behavior for their own benefit is extremely rare in mammals because our blood brain barrier is so effective in keeping most pathogens out. But not this one.

Why Cats Rule the Internetz: If this parasite can profoundly affect rats, what about people? Studies have shown that infected men have altered behavior and personality including a tendency to disregard rules, higher suspiciousness and jealousy. Schizophrenics are more likely to be infected with Toxoplasma, and there are disturbing links to suicide as well. A 2006 study published in the journal Proceedings of the Royal Society B found that antipsychotic drugs, commonly used to treat schizophrenia, reverse the fearlessness effects of T. gondii in the brain. This is why the CDC classifies toxoplasmosis as a neglected parasitic disease

Image: A rosette of Toxoplasma gondii cells by Markus Meissner (University of Glasgow, UK) from Nature Methods



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111 Responses to Toxoplasma: Cats, Rats and Mind Hacks

  1. Terry McNeil says:

    I knew about toxoplasma, I had no idea of the detail.  Thank you.

  2. Rajini Rao says:

    David Flick , in naturally colored animals, yes indeed! However, these bright colors come from fluorescent dyes or antibodies used to see the cells under a microscope 🙂

  3. Rajini Rao says:

    Terry McNeil , same here! I casually looked it up to add something interesting to go with the pretty image and I was blown away by the bizarre details.

  4. always informative, Rajini Rao 🙂

    lol @ why cats rule the internetz!

  5. Rajini Rao says:

    Hehe, I knew G plussers would appreciate that sly comment Phill Hocking .

  6. Kawthar A says:

    My grandma used to tell me that pregnant women must stay away from cats, but I have never known why, thanks Rajini Rao I know now 🙂

  7. Rajini Rao says:

    Kawthar AL ABDALLA , indeed your grandma was right. Here in the US, a pregnant woman is asked a series of questions on her first visit to the obstetrician and “Do you own a cat?” is one of them.

    To clarify, if I recall the instructions, she has to be careful of cat litter, not the cat 🙂

  8. Kawthar A says:

    Ah ok..many traditions are followed without even know the reasons, but I have to admit some of them has a good reason 🙂 to be honest, I have no idea if these questions are asked to the pregnant women by the doctors in Syria. We learn new things everyday 🙂

  9. Rajini Rao My goodness, a particularly fascinating instalment today, thanks. (I have a natural aversion to cats, fortunately.)

  10. Fascinating! Why has nobody weapon used this parasite yet? I’m not for biological warfare but I find the field innovative & fascinating… & deadly

  11. Forget animals….save yourself and others around you…

  12. Rajini Rao says:

    Kawthar AL ABDALLA maybe you’ll visit those types of doctors somedays 😉

    Mike McLoughlin , some of us are crazy without any parasitic intervention at all 🙂

  13. Rajini Rao says:

    Shah Auckburaully , now why did you think of that? 🙂

    Actually, the behavioral study I read was done on people in the military. I assumed it was only because of convenience in following up a cohort of people in a database.

  14. <——- raises hand for 'crazy without parasitic intervention' club :/

  15. Kawthar A says:

    lol..I have already got enough of misery 😉

  16. Mad B says:

    Shah Auckburaully it is already used as a weapon to overload internet, it is called #caturday

  17. Rajini Rao says:

    Shaker Cherukuri , exposure to the parasite is dangerous to the fetus. Cats are the only “definitive hosts” where the parasite reproduces (and exits through feces). Other mammals, like ourselves, are merely carriers.

  18. Rajini Rao says:

    Madjid Boukri, seems like a legit hypothesis: people who post to #caturday are more likely to be carriers of Toxoplasma? 🙂

  19. Sue Bosbury says:

    You only have to wear gloves or get someone else to change the litter box! 

  20. Rajini Rao says:

    Sue Bosbury , that’s reassuring. Good hand hygiene goes a long way.

  21. or try not to catch that thing in the air getting girls pregnant. 

    their feet! 


  22. i think the post does indicate that M Monica – but perhaps it can be more obvious?

  23. Rajini Rao says:

    Edited, M Monica! Darn, I thought I had a good theory for my next grant application 🙂

  24. This entity (Toxoplasma gondii) might be a predisposing/important factor in suicidal tendency actualy !

  25. Oh gosh… This still blows my mind, and is more than just a little creepy! I remember when I first read about it about a year ago, it seemed so strange that friends I discussed it with thought I was pulling their leg.

  26. We are surrounded by bacteria and viruses. The best defense is to stay healthy inside and out.

  27. Rajini Rao says:

    Laurent DUBET , I did come across studies linking the infection with higher levels of suicide although I did not dig too deep into how good the correlations were. One paper even implied that accident rates and all sorts of deaths were increased by Toxoplasmosis!

    Rashid Moore , good point about there not being any vaccine. Cat ownership is so common, that this is definitely worth broadcasting.

  28. Rajini Rao says:

    M Monica , I’m sure many of us were not aware that dogs can transmit infections to their human friends, so thanks for that. Reptiles (turtles, lizards, geckos..and yikes..snakes) are definitely a risk because they carry Salmonella.

  29. very useful,thanks for the post!

  30. Rajini Rao says:

    Excellent, thanks for the references Raymund Kho K.D. .

  31. Raymund Kho K.D. is a pretty handy dude! been loving your neuropsychology posts lately bud!

  32. Interesting to learn about this.

  33. Maybe that’s why I love my cat so much!!!

  34. Liz Krane says:

    My dogs gave me fleas once, but that’s about it, thankfully. 🙂 I wonder… is there a simple test to find out if you have toxoplasma then?

  35. Rajini Rao says:

    Liz Krane , yes there are tests for toxoplasma. Most commonly by testing for an antibody in the blood: The cerebrospinal fluid can also be examined microscopically for the parasite, but that’s a lot more invasive.

  36. It seems we forget here one of the most common way to get intected: salads, unwashed fruits and vegetables and contact with soil.

    For farmers or horticulturalist, it is almost a must have disease. Geologists like me have for common practices to lick a stone in order to have the proper colour and texture. I guess we should be considered as an exposed population as well.

  37. Liz Krane says:

    Rajini Rao Thanks for the link! Interesting. I was also curious if it’s problematic if you get infected with toxoplasma before becoming pregnant. Says here: “Some experts suggest waiting for 6 months after a recent infection to become pregnant.”

  38. Btw, disregard to rules is a quality for me.

  39. Rajini Rao says:

    Olivier Malinur , re. vegetables, this is from Wiki, “In 1959, a study in Bombay found the prevalence of T. gondii in strict vegetarians to be similar to that found in nonvegetarians.”

  40. Normal, because both probably are washing their vegetables and fruits

  41. Liz Krane says:

    Thex Dar lol! Seems rather unlikely. If I do have tapeworms, I’ve had them for a good 15 years now so may as well keep em. (Kidding, of course!)

  42. Chad Haney says:

    I don’t need another reason to avoid #caturday , 😉

  43. Rajini Rao says:

    Chad Haney , what about #fidofriday ? Thex Dar just warned us off our doggie companions 🙂

  44. Chad Haney says:

    My dog gets FrontLine flea protection and a heartworm pill that is also somewhat effective against tapeworms and hookworms. So I can still hug my dog as much as she will tolerate.

  45. Kevin Clift says:

    There was an article in The Atlantic and a subsequent Reddit AskScience that some people here might like:

  46. James Cannon says:

    Rajini Rao thanks the enlightenment!

  47. ajay sawant says:

    Hi there. Nice post

  48. Beautiful and Vicious!

  49. Jane Ellert says:

    Don’t post chain letters it’s just” spam” people don’t like. 

  50. i didn’t need to know that…

  51. Rajini Rao says:

    Thanks, Jane Ellert 🙂 I deleted that chain comment.

  52. Jane Ellert says:

    cool picture though!

  53. Pregnant women do not need to avoid cats. And the only cats at risk of transmitting toxoplasmosis are outdoor cats, and it only lives in fecal matter for a very limited amount of time. Too many cats are given away to shelters, and likely euthanized, because of a misunderstanding of this topic.

  54. Rajini Rao says:

    Kelly Millard , thanks. The recommendations by the CDC have been posted here, but just to be sure, here they are:

    Do I have to give up my cat if I’m pregnant or planning on becoming pregnant?

    No. You should follow these helpful tips to reduce your risk of environmental exposure to Toxoplasma.

    Avoid changing cat litter if possible. If no one else can perform the task, wear disposable gloves and wash your hands with soap and warm water afterwards.

    Ensure that the cat litter box is changed daily. The Toxoplasma parasite does not become infectious until 1 to 5 days after it is shed in a cat’s feces.

    Feed your cat commercial dry or canned food, not raw or undercooked meats.

    Keep cats indoors.

    Avoid stray cats, especially kittens. Do not get a new cat while you are pregnant.

    Keep outdoor sandboxes covered.

    Wear gloves when gardening and during contact with soil or sand because it might be contaminated with cat feces that contain

    Toxoplasma. Wash hands with soap and warm water after gardening or contact with soil or sand.

  55. Wow ! Good to know !

  56. Camille says:

    Interesting Info

  57. Is is all cats ? Inside cats ? Or just the ones that go outside ?

  58. Rajini Rao says:

    Elizabeth Ledo more likely outdoor cats. Depends on whether indoor cats are fed raw meat or not.

  59. So beautiful – but deadly!

  60. Rajini Rao Thank you I feel better knowing that !

  61. Rob Kook says:

    Is there a medication to get rid of the parasite? I let a 300kg usuri tiger lick my arm and don’t respect rules. There’s no other explanation 🙂

  62. Rajini Rao says:

    A tiger licked your arm? You can take on any parasite, Robko Kook 😀

  63. Well this kind of explains me then…….shit

  64. Alice Haugen says:

    It sounds like all men should be added to the list of who should avoid cats!

  65. Rajini Rao says:

    Alice Haugen , I have to confess that there were effects reported on women too, but different. I was running out of space..didn’t want the post to be too long 🙂

  66. I’ve heard about this virus before. If it can affect people it is pretty amazing… and scary!

  67. Rajini Rao says:

    cassandra lucic , interesting organism! It’s a single celled parasite though, not a virus. So it has a nucleus and organelles within its cell. The malarial parasite is similar.

  68. Rajini Rao I read that the organism manipulates people to be attracted to other people with the organism. Not sure if this is true though. Scary parasite nonetheless! 

  69. Gary Strohl says:


    Don’t send me no suff

  70. Rajini Rao says:

    cassandra lucic  there is good data that it manipulates rats, which are a carrier organism. It would be much harder to show that humans can be manipulated because there are so many variables between people and of course, we cannot be in a controlled study as rats! 🙂

  71. Rajini Rao says:

    Micah Bodhi , there’s no hype the comments. Numbers for infected cats from Wikipedia are as follows: The seroprevalence of T. gondii in domestic cats, worldwide, has been estimated to be around 30-40%.[59] In the United States, no official national estimate has been made, but local surveys have shown levels varied between 16% and 80%.[59] A 2012 survey of 445 purebred pet cats and 45 shelter cats in Finland found an overall seroprevalence of 48.4%.[60] A 2010 survey of feral cats from Giza, Egypt, found an overall seroprevalence of 97.4%.[61]

    There’s more on the Wiki page:

  72. Rajini Rao Good point. I was intrigued by this parasite because it apparently affects peoples minds. I think more people should be aware of it. And the fact it is carried by cats. Good post. 🙂

  73. Micah Bodhi Not sure if you’re comment was addressed to me. But I’ll read it. Like I said it is an intriguing parasite.

  74. Micah Bodhi lol! That explains why I couldn’t find it in your posts! Oh well. 

  75. Rajini Rao says:

    Yes, of course I did Micah Bodhi . In response, I cited several other studies that showed much higher rates of serological positives in domestic cats. I’m quite ready to provide references from PubMed if you prefer those. The chief mode of infection to humans is via cats and contact with their feces. 60 million Americans are infected and about a third of the world population. So those numbers would indicate that transmission to humans is significant. The point of this post has nothing to do with staying away from cats or that cats are a danger: indeed, clinical symptoms in healthy humans are mild or absent. I am bringing up the intriguing aspect of this parasite on whether it links to psychological effects in humans. I’m trying to explain how the lattter is well documented in rats but still speculative in people. That was my post in sum, don’t take it off tangent or misinterpret it please.

  76. Tom Miller says:

    Rajini Rao Check out this great Radiolab episode.  It has a segment on toxo:

  77. Divy says:

    This is so redefining…. awareness is the only cure or this can be eliminated too? …. Thank you Rajini Rao for this so very educative post… it should be wide spread!!!! 

  78. Helmi Jr. says:

    To cat owners, don’t freak out. As long as you stay hygienic, it will all be good. and hopefully somebody won’t get this info the wrong way, and start treating cats/ stray cats like shit whenever they see ones. Just saying you know because a lot of fools out there would be using even the tiniest excuse to be cruel to animals. Even birds out there got their own flu. And it’s deadlier than this.

    Thanks for the good info btw.

  79. Rajini Rao says:

    Helmi Jr. , thank you – this is not a post about avoiding cats, and ill treatment of any animal is horrible. The comment thread and post make this clear, but it is worth repeating. 

  80. Thanks for your nice efforts

  81. John Sanders says:

    What do you do to treat the pategen

  82. John Tropea says:

    A Conversation with Robert Sapolsky on toxoplasma – see video and transcript

  83. Toxo exists as two forms in intermediate hosts (hosts other than felines): a fast growing tachyzoite and a slow growing (virtually dormant) bradyzoite, Anti-folate drugs can control the tachyzoite, but no medicine exists that can eliminate the bradyzoite because it stays inside your cells in a thick cyst wall and grows very slowly if at all. So Toxo infection is permanent, but considered benign for all of those who are not immunosuppressed. It is tempting to speculate that these dormant cysts can alter human behavior, but the studies are only correlative and difficult to draw firm conclusions due to many confounding variables. The studies performed in rodents are much more convincing and the effect seen in those animals are more convincing. One other note…there is no strong evidence that Toxo is sexually transmitted as implied above. Most common modes of transmission are raw/undercooked meat (in this case, you are consuming those bradyzoite cysts which survive the stomach and go on to infect you through the intestine!), water contaminated by oocysts expelled by an infected cat (they are stable in the environment for up to a year in water or soil), and oocysts contracted from litter box, garden, sandbox, etc. Thanks for the post and helping to make this common but obscure parasite more of a household term!

  84. Very informative and potentially life-altering article Rajini Rao And a  great image of a dangerous beauty, to go with it.  Thanks for sharing

  85. Rajini Rao says:

    Thanks, good to hear from you, John Christopher . I hope it was informative but not scary.

  86. ‘Scary’ is too strong a word 🙂 but I definitely found it interesting (perhaps even ‘alarming’) since I have long been a ‘cat person’  Rajini Rao 

  87. Guitar Dave says:

    True , you can’t be too safe.

  88. Admirable organism! Thank you for the post and the picture! Such an incredible ability to modify the host behaviour to complete its life cycle!

  89. Ka Kakrpa says:

    Very interesting!  Would treating the latent form of toxoplasmosis in humans likely resolve/alleviate psychological illness (referring to specific reference of schizophrenia in post, but am curious about illnesses such as depression, OCD, etc. as well)?  Are there any studies on this?  Any known cases where antimicrobial therapy alleviated/resolved psych symptoms/manifestations? Thanks for the great post – very interesting!

  90. Thanks again. Amazing!,!

  91. Guitar Dave says:

    Question : If toxoplasma affects schizophrenics why not treat them for the toxoplasma and at least reduce their suffering ? Has this been addressed by the mental health doctors yet or is it still too early ?

  92. Rajini Rao says:

    Guitar Dave , it’s the other way around. Drugs already in use to treat schizophrenia reduce the psychological effects of toxoplasma infections.

  93. Guitar Dave says:

    Do forgive me I didn’t know . Can it be detected early before it has time or a chance to do damage ?

  94. Guitar Dave says:

    I hope your Memorial Day is a good one .

  95. Rajini Rao says:

    Guitar Dave , there are some good tests, yes. And thank you for your wishes, I hope you are having a good holiday too 🙂

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