In the past few days, a wave of articles, Facebook posts, and tweets seemingly struck a major blow for #teamdog: dramatic headlines informed us that a recent study found that cat ownership causes people to go crazy. Most of the articles later clarify that the study, which looked specifically at schizophrenia (not “craziness”), did not find that that house cats themselves are to blame, exactly. The guilty culprit is the parasite Toxoplasma gondii (also known as T gondii or toxo), found in cat poop.
But if you read the original study, published this month in Schizophrenia Research, you’ll find neither of those points are accurate. I don’t particularly like cats, but even I think they’re getting kind of a bum rap here.
Let’s talk about the study. Researchers Torrey, Simmons, and Yolken set out to replicate earlier findings that suggested childhood cat ownership is a risk factor for schizophrenia. The new study is based on a two-page questionnaire filled out by attendees at the 1982 National Alliance for the Mentally Ill (NAMI) annual convention. The original, unpublished survey included a question on cat and dog ownership up to age 17; these researchers specifically focused on participants exposed through age 13. There was no control group with the original questionnaire, so researchers supplemented a 1991 survey by the Veterinary Medical Association that looked at cat ownership in 10 different groups—they chose the one that they thought best matched the 1982 participants. No data was collected on whether individuals in this later survey were diagnosed with schizophrenia. Neither study provided detailed information on outdoor versus indoor cats or exposure to cats outside the home.
Results showed that 50.6 percent of individuals with schizophrenia owned a cat between birth and 13 years of age. In the control group, 42.6 percent owned a cat. The difference was statistically significant and researchers concluded that, as compared to the general population, individuals with schizophrenia are more likely to have owned a cat in their childhood. Although there is no additional data in place to check for confounding variables, I’ll buy the possibility of the connection—it is consistent with a few prior studies that suggested the same.
But of course, there was no indication in this or other studies that cat ownership causes schizophrenia.
Here is the only reasonable conclusion based on this study: researchers identified a possible link between cat ownership prior to the age of 13 and the later development of schizophrenia. Further research with a more representative national sample would be required to verify this finding and determine the cause of this risk factor. If confirmed, cat owners may wish to consider the presence of children in the home when deciding on cat ownership.
Here is an unreasonable but much more widespread conclusion based on this study: Toxoplasma gondii, probably caught from your cat, may cause you to develop a major mental illness. Shortened: your cat’s going to make you crazy! Like a crazy cat lady!
One might rightfully wonder how Toxoplasma gondii got wrapped into the reporting on this study. Though the research in no way included data on the parasite (the cats owned may or may not have been infected; people may have been exposed in other ways, such as a caregiver with a cat or playing outside), the researchers mention in both the abstract and the discussion that “if true, an explanatory mechanism may be Toxoplasma gondii.” It’s an if. Absolutely no data was collected in this study on whether pet cats were infected with Toxo.
Interestingly, a completely unrelated study published in April in the journal Acta Psychiatrica Scandanavica did look at T gondii specifically, though not how or when people were exposed. Researchers reviewed 50 studies examining the prevalence of antibodies to the parasite (indirectly indicating prior exposure) in individuals with any psychiatric disorders. They found a significant correlation between signs of prior infection with T gondii and schizophrenia, bipolar disorder, addiction, and obsessive-compulsive disorder. This meta-analysis, however, did not look at cat ownership as a possible cause of infection.
So: we’ve got a classic case of bad science reporting algebra going on here. Study A shows cat ownership in childhood may be associated with later diagnosis of schizophrenia. Separately, study B shows infection with Toxoplasma gondii at some stage in life may be associated with schizophrenia. Common knowledge shows that cats are carriers of Toxo and a source of human infection with the parasite. So somehow study A was added with study B and the conclusion is Science Reports Crazy Cat Lady Stereotype May Be True!!
According to the CDC, more than 60 million Americans carry toxo (by some estimates, the parasite infects nearly half the world’s population). People are far more likely to become infected through gardening and consumption of uncooked meat than from their feline companions. Importantly, most infected will suffer no or very mild ill effects. Vulnerable groups include pregnant women (who can pass the infection on to the fetus) and the immunocompromised. This recent study suggests that infection as a child may be a risk factor for development of mental illness later in life.
If you are concerned about catching T gondii from your cat, there are ways to minimize your exposure. The oocytes (eggs, basically) of the parasite are only infectious when poop is more than a day old. So, while that fancy kitty litter may promise to keep the smell at bay for a month, if there is a child, pregnant woman, or other immunocompromised person in the house, it’s best to clear the litter box daily and keep it out of reach. (This is an excellent excuse for anyone in those categories to get out of this odious chore.) Sandboxes should be covered to prevent their use as giant litter boxes by outdoor cats. Cats can only be infected if they hunt or eat wild animals or if fed raw meat, so keeping your cat indoors will help protect both it and you. Wash your hands thoroughly after dealing with cat poop ( you should do this anyway). And you can find more information on Toxoplasma gondii here.
The American Pet Products Association (APPA) estimates that 30 to 37 percent of American homes have pet cats. Many studies have shown that owning a pet can be beneficial to overall health—and neither of these studies suggest a reason that we should give up our four-legged companions. The bottom line is: fear of schizophrenia is not, and has never been, a good reason to get rid of your cat. The fact that cats are objectively inferior to dogs remains the most convincing argument.
Caroline Weinberg is a doctor with a masters in public health and a background in international healthcare. She is committed to health education and thinks it’s time the media starts accurately reporting on science and health.