Cats and Schizophrenia

When we think of cats, many of us are reminded of rather ornery creatures that are always sneaking and lurking around. My best friend growing up had a pet cat who would always sit in the dark corner of her basement and almost never come out. It doesn’t help that black cats are also associated with bad luck, particularly around the spookiest time of the year. So yes, cats don’t necessarily have a good rep to most of us. But, while some of us hate them, some of us are self proclaimed “cat-lovers”. Either way, I’m sure we all know someone who has a cat or have owned one ourselves (perhaps not by choice), considering they are the second most popular house pet (after dogs, of course). However, not many of us know people with schizophrenia. About 30.4% of the United States’ population owns a cat, but only roughly 0.007% of people in the US have schizophrenia (roughly 2.2 million). So what do cats and schizophrenia have to do with each other? A surprising statistic relate the two: a little over half of people with schizophrenia owned a cat at some point in their childhood.

Cute five month baby with black cat

Cute five month baby with black cat

Hypothesis: The parasite Toxoplasma gondii (T. gondii) found in cats can be passed onto humans, entering the brain and forming microscopic cysts. Scientists propose that the bacteria remains latent for several years, and not actually affecting most people that have T. gondii in their brains, but still affecting some later in adolescence (when symptoms of schizophrenia typically begin to emerge) by messing with the connections between neurons, which causes the disease. Therefore, the hypothesis is that the families of people with serious mental illness were more likely to have pet cats during the person’s childhood (Foley, 2015).


Null hypothesis: There is no relationship between having mental illness, particularly schizophrenia, and the ownership of cats. This is what researchers are trying to disprove.

Experiment: A 1982 questionnaire was distributed to 165 families belonging to the National Institute of Mental Illness. The NAMI consisted of families in which at least one member was diagnosed with schizophrenia, schizoaffective disorder, or bipolar disorder or severe depression (with psychotic features). The most important question, one amongst many in the 2 part page questionnaire that included additional questions about breastfeeding, developmental milestones, coordination, rheumatoid arthritis and multiple sclerosis, asked if there was a cat living in the house with the affected family member at any point between birth and the age of ten. The control group of this experiment were the family friends of these NAMI families who filled out the same questionnaire, and whose children had not developed any mental illness.

Results: 84/165 (50.9%) of the cases and 65/165 (39.4%) of the controls responded yes, they did in fact own a cat. No causal relationship is shown, therefore also ruling out reverse causation (having the gene for schizophrenia causes someone to own a cat in their childhood). However, there still is a link. So was the hypothesis proved? Based on the results of the survey, more than half of the families in the NAMI that completed the survey owned cats. This is a significant amount, therefore proving the hypothesis that the families of people with serious mental illness were more likely to have pet cats during the person’s childhood than they were not.

This study by researchers E. Fuller Torrey and Robert H. Yolken, suffered from the file drawer problem, because it all of the data was collected in 1982 but not published until 1995.


Prevention: Obviously, people are not going to just stop owning cats. However, to prevent the spread of T. gondii to yourself, you should avoid cat feces or be very careful with how you handle it (if you must). You should probably take precautions such as wearing gloves and/or immediately washing hands afterwards. Cats pick up the bacteria from preying on rats, who are congenitally transmitted it at birth. It can also be transmitted through the eating of undercooked, contaminated meat. Many of us remember the E.Coli outbreak and how that affected the food we bought. Unfortunately, is impossible to tell if meat containing T. gondii has the bacteria or not. It’s up to you whether or not the benefits outweigh the risk, with eating meat as well as owning a cat.

No wonder most folks are dog lovers.

Works Cited

Study: A common cat parasite could be making humans mentally ill

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