Do Cats Cause Mental Illness?

Toxoplasma gondii
Toxoplasma gondii. My thanks to Wikipedia for the image.
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A very recent study published online on 22 February 2017 debunks the theory that cats cause mental illness in people. This is an evergreen topic of discussion and there is conflicting information on the Internet as to whether the domestic cat causes mental illness amongst human companions because the cat is the primary host of the protozoan parasite toxoplasma gondii.

Tens of thousands of words have been written in news articles on the Internet based upon research studies which stated that schizophrenia and mental health issues in people could be caused by the domestic cat having transmitted the parasite to humans via their faeces (a zoonotic disease). The news articles have sometimes stated confidently that the world is going mad because of the domestic cat!

The truth is that although there have been no conclusive studies on this matter, the online news media created what I would call fake news of a sort which in turn led to cat haters denigrating the cat and seeking the extermination of the feral cat.

We now have a further study which I believe puts the record straight to a certain extent. It comes out of the University of London, UK.

The research is published online. You can read the summary, if you wish, by clicking on this link (it is technical). It is entitled: Curiosity killed the cat: no evidence of an association between cat ownership and psychotic symptoms at ages 13 and 18 years in a UK general population cohort.

The conclusion is that while pregnant women should be cautious about handling cat litter (I have covered that issue in previous articles – please use the custom search engine), the study “strongly indicates” that can ownership in pregnancy or during early childhood does not pose a risk to adolescents of contracting psychotic experiences (PEs).

The team who carried out the research criticise previous studies, remarking:

“Previous studies reporting links between cat ownership and psychosis simply failed to adequately control for other possible explanations.”

The way I read this is that previous studies were not carried out accurately enough in not taking into account other possible causes of psychosis or mental health. Research studies are very complicated and you need to build into the model (the method that the study is based upon) many factors which may influence the outcome of the study and which may distort its conclusions. Computer programs can do this. The researchers need to introduce these programs and methods in order to arrive at a clean result.

I’m not, by the way, necessarily supporting this particular study but it is good to see one which redresses the balance.

In this study 6,705 children age 13 and 4,676 children age 18 were examined to assess associations between cat ownership and psychotic experiences1. The adjustments were made for sociodemographic and socio-economic factors and also dog ownership and household characteristics.

To re-emphasise, Dr Francesca Solmi, the lead researcher, said that:

“Previous studies reporting links between cat ownership and psychosis simply failed to adequately control for other possible explanations. Once we controlled for factors such as household overcrowding and socio-economic status, the data showed that cats were not to blame.”

So in answer to the question in the title, “Do Cats cause mental illness?” we would have to say that this is still work in progress if we are to be completely honest even though I’m a cat lover and animal advocate. In short we don’t quite know yet but the strong indications are that cats do not cause mental illness in people.

You might also wish to look at the question from a different angle. If the cat did cause mental illness in people, primarily cat owners and family members, it would have come to light by now. We would know about it through personal experiences and masses of anecdotal evidence. In addition, I would have thought that the domestic cat would not be as popular as it is in America and all over the planet if there was the hint of a possibility that he/she made their owners mentally ill. People don’t believe the earlier studies linking cats with mental health issues.

Note 1: the researchers used data from the Avon Longitudinal Study of Parents and Children (ALSPAC).

See also a Prezi presentation on prevention of human toxoplasmosis.

14 thoughts on “Do Cats Cause Mental Illness?”

    • So, it is perfectly okay with you that your pregnant neighbor miscarries or still-births their HUMAN child; or their child is born with microcephaly or hydrocephaly (the VERY same congenital maladies caused by the much-feared mosquito-borne Zika virus), ADHD, autism, blindness, etc., just as long as you get to feel better about your own life for pretending to be the parent of your pet? And you are just THAT desperate to feel needed by some other living thing in your own life that you are willing to sacrifice even the lives of other humans to attain that? Did I get that right?

      Google for: Toxoplasma gondii airborne
      Or: Toxoplasma gondii survives hydrochloric acid or bleach

      Then come back and tell us again how “simple hygiene” will prevent being infected.

      WHY do you all blatantly LIE so often and so much?

      • You can’t blame cats for everything. Honestly it would be better for you to do absolutely nothing the rest of your life than spend one more day vilifying cats the way you do. You’re only proving that a little bit of knowledge, the pudding skin of biology 101, and a butt-load of hate is a very dangerous thing. You really don’t understand or care about the real world. The more you try to portray yourself otherwise only proves it. And no, I’ll not argue with you, because that’s the only thing you really want. You’re the literary equivalent of cancer.

        • Thanks Albert. Nice work. This article was bound to bring out the trolls and people who like to denigrate the domestic and feral cat. I knew it would and I knew I would have to deal with them. These people are on a mission. The mission is to denigrate and if necessary hurt feral cats.

          • Yep, and I’d point to our sorry state of education if these people actually received a H.S. or even junior high diploma, as they don’t know the difference between possibility and probability. How did they even find their way to school in the morning? Their teachers must have given up because there was just no reasoning with them.

  1. Pretty narrow field of research, only 2 ages? What about all the studies that proves it causes IED (intermittent explosive disorder: road-rage, spousal abuse, etc.) in adults? Or what about all that memory loss in seniors? And what about all the studies that links it to autism, ADHD … oh that’s right, they’re still grasping at straws trying to find anything less than horrific about T. gondii. Does the fact that this cat-vectored pathogen is second only to Salmonella when it comes to causing *fatal* food-borne illness in America give you a great relief that it’s not #1 yet? (Which, by the way, all your food becomes infected directly from cat-feces, but let’s not mention that, shall we?)

    • Well, I agree that the study concerns kids but I have referred to and linked to the study. You have bandied around all kinds of information but no reference to the sources. I can’t believe it. You have to do much better to be believable.

  2. Well articulated Michael. Research is ongoing, but the latest I found states the following positives:

    Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii.[1] Infections with toxoplasmosis usually cause no symptoms in adult humans.[2] Occasionally there may be a few weeks or months of mild flu-like illness such as muscle aches and tender lymph nodes.

    [50] Numerous studies have shown living in a household with a cat is not a significant risk factor for T. gondii infection

    Toxoplasmosis is generally transmitted through the mouth when toxoplama gondii cysts are accidentally eaten, spread by eating poorly cooked food that contains cysts.
    Also, Ingestion of unwashed fruits or vegetables that have been in contact with contaminated soil.

    Prevention is by properly preparing and cooking food. It is also recommended that pregnant women not clean cat litter boxes.[6] Treatment of otherwise healthy people is usually not needed. In addition to cats, birds and mammals including human beings are also intermediate host of the spores and are involved in the transmission process.

    Up to half of the world’s population is infected by toxoplasmosis but have no symptoms.

    Treatment is often only recommended for people with serious health problems, such as people with HIV whose CD4 counts are under 200 cells/mm3.

    In the United States, data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2004 found 9.0% of US-born persons 12–49 years of age were seropositive for IgG antibodies against T. gondii, down from 14.1% as measured in the NHANES 1988–1994.[70] In the 1999–2004 survey, 7.7% of US-born and 28.1% of foreign-born women 15–44 years of age were T. gondii seropositive.[70] A trend of decreasing seroprevalence has been observed by numerous studies in the United States and many European countries.[69]

    A 2016 study using the Dunedin cohort found that “there was little evidence that T. gondii was related to increased risk of psychiatric disorder, poor impulse control, personality aberrations or neurocognitive impairment”.[144]

    1. ”Parasites – Toxoplasmosis (Toxoplasma infection) Epidemiology & Risk Factors”. March 26, 2015.
    2. Hunter, CA; Sibley, LD (November 2012). “Modulation of innate immunity by Toxoplasma gondii virulence effectors”. Nature Reviews Microbiology.
    6. “Parasites – Toxoplasmosis (Toxoplasma infection) Prevention & Control”. January 10, 2013.
    69. Pappas G, Roussos N, Falagas ME (October 2009). “Toxoplasmosis snapshots: global status of Toxoplasma gondii seroprevalence and implications for pregnancy and congenital toxoplasmosis”. International Journal for Parasitology.
    144. Pearce BD, Kruszon-Moran D, Jones JL (Aug 15, 2012). “The relationship between Toxoplasma gondii infection and mood disorders in the third National Health and Nutrition Survey”. Biological Psychiatry.

    Just wash your food, cook meats thoroughly and keep your fingers out of your eyes. 50% chance you’ve already had it, as in with millions of other things in life; it’s not a problem unless you’re extremely compromised, like with HIV.
    Go pet your cat!

  3. Here’s an example of the… (deleted by Admin)

    You cannot insult my friends you ignorant bastard. F Off. (Michael Admin)

    • I would worry about keeping any “friends” who are doing all in their power to have you and your site shut-down permanently from those cyber-stalking and cyber-bullying careers of theirs in which you also engage. Don’t say you’ve not been warned. You knew this was coming for a long time now. Boo hoo, too bad, so sad. You can all dish it out, but you can’t even take a tiny fraction of it? There’s much much more to come … Be afraid, be very afraid. You can thank your other “friend” Linda Ashton for starting this all. 🙂

  4. But you’re still willing to kill your neighbor’s unborn child or make them go blind, even if the mental-illness side of the issue isn’t true. How nice of you. That make your cat-hobby alright then!


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