There’s a popular idea, supported by a few studies and lots of media stories, that cats can give people infections that cause serious mental illness, including schizophrenia, major depression and even suicidal behavior.

You can relax now.

The latest study, the most comprehensive one to date, took a long, careful look at those associations and found no evidence that cats are a threat to our mental well-being.

But there are a few other risks that you should know about that relate to living with our feline friends.


Cats, especially those that go outside or eat raw meat, often carry toxoplasmosis, an infection caused by a parasite. It’s present in their feces and can infect people—when they change kitty litter, for example.

In mice, the infection appears to affect behavior—making them less afraid of cats, which helps the parasite, since it needs to get into cats to complete its life cycle. (When a cat eats an unprotesting infected mouse, the parasite is home free.) Along the way, there have been statistical suggestions that toxoplasmosis may affect human emotional health, too—negatively. But these studies have been small.

To get a more scientifically reliable answer, researchers in New Zealand analyzed data from 800 people who had been followed for nearly 40 years, literally from the day they were born. Over the years, the participants had blood tests and many assessments looking at psychiatric disorders, personality traits, cognitive performance and indicators of poor impulse control (a risk factor for suicide). Blood tests showed that 28% had been infected with toxoplasmosis, and their data was compared with data from others who had never been infected.

Results? There were no statistically significant links between toxoplasmosis infection and any of the markers for behavioral illness.

Is this the final word on the subject? Like all studies, this one will be stronger if other studies confirm it. But this new, large-scale, long-term statistical analysis goes a long way toward reassuring us that the “cats are driving humans crazy” worry is, at the least, exaggerated.

What about other worries?


Even though your cat isn’t likely to drive you crazy—at least in the clinical sense—it still makes sense to take precautions against toxoplasmosis. While about 16% of Americans have been infected, usually with no symptoms, in rare cases it can cause serious eye problems. Of greater concern is the effect on pregnant women. Toxoplasmosis can be transmitted to the fetus during the pregnancy, and babies can end up blind or with neurological complications.

So it’s prudent for cat owners to wear gloves when changing kitty litter or to wash their hands immediately afterward. Since toxoplasmosis can also linger in meat and in soil, it’s a good idea for everyone to avoid raw or undercooked meat, and, after gardening with bare hands, wash them.

Cats can harm you in other ways, too—they transmit pathogenic bacteria through their claws and saliva, and they can bring fleas into your home, among other dangers. To learn more, see Bottom Line’s article, 6 Ways Your Cat Can Make You Sick—or Even Kill You.

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