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How Your Cat Could Be Making You Mentally Ill

A 2016 study has found that people with a rage disorder are over twice as likely to have been exposed to a parasite found in cats. Do pet lovers around the world need to worry?
Photo by Jovana Rikalo via Stocksy

Cat owners have multiple problems to worry about, including the scourge of serial cat killers, how their sex lives may affect their beloved pets, and how men with dogs are hotter than those with cats. They may now have to add parasitic infections to that list.

A 2016 study published in the Journal of Clinical Psychiatry has found that individuals with a rage disorder are more than twice as likely to have been exposed to a common parasite that is passed from cats to humans.


Toxoplasmosis is a relatively innocuous parasitic infection transmitted through the feces of infected cats, contaminated water, and undercooked meat. Cats are the only hosts in which the toxoplasma gondii parasite can reproduce. The parasite's eggs, known as oocysts, are then shed through the cat's feces.

According to International Cat Care, 20 to 60 percent of all cats will be infected with the parasite, but only a minority will show signs of the infection. An estimated 20 to 30 percent of people in the US and the UK will be infected at some point in their lives.

"Our work suggests that latent infection with the toxoplasma gondii parasite may change brain chemistry in a fashion that increases the risk of aggressive behavior," said senior study author Emil Coccaro, the chair of psychiatry and behavioral neuroscience at the University of Chicago.

In a study of 358 adults, researchers found that those diagnosed with intermittent explosive disorder—a mental illness linked to angry outbursts like road rage—were over twice as likely to test positive for toxoplasmosis exposure. These individuals also scored significantly higher on tests for anger and aggression.

Researchers said that more work needs to be done on the relationship between toxoplasmosis and anger. "Correlation is not causation, and this is definitely not a sign that people should get rid of their cats," said study co-author and University of Chicago associate professor Royce Lee.


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"We don't understand the mechanisms involved—it could be an increased inflammatory response, direct brain modulation by the parasite, or even reverse causation where aggressive individuals tend to have more cats or eat more undercooked meat. Our study signals the need for more research and more evidence in humans."

It's not the first time that toxoplasmosis has been associated with mental health issues in humans. Previous studies have linked the parasite to psychiatric issues such as suicidal behavior, bipolar disease, and schizophrenia. The CDC also advises pregnant women pass litter box changing duties on to someone else, as toxoplasmosis can be passed to the fetus and cause serious health problems like blindness, epilepsy, and mental retardation.

Your cat loves you, and so does his parasite. Photo by Mauro Grigollo via Stocksy

Given the potential downsides, is it time to reassess your days as a cat lover? British Veterinary Association junior vice president Gudrun Ravetz cautioned against driving Mittens to the pound just yet.

"I think these kinds of studies highlight the importance of general hygiene precautions," Ravetz told Broadly. "There are no studies that show that owning a cat increases your risk of getting toxoplasmosis. In fact, most people will get contact through raw and undercooked meat. Vets working with cats are certainly no more likely to get infected than the general population, and that includes people who don't own cats."

"We would always recommend good personal hygiene with any animal. If you're pregnant, avoid cat litter out of good practice. If you're handling cat litter, use gloves and get rid of it straight away. The more important thing is that there are very well documented health and wellness benefits to owning any pet, and that includes cats. But these studies are important because they reiterate the importance of general hygiene and taking sensible precautions."

When I asked cat owners if they would give up their cats if their mental health was at risk, the answer was a resounding no. "I guess as long as I'm the one 'suffering,' it's OK," speculated Ami, a film editor who owns a five-year-old cat and has just acquired another kitten. "If I become rage-y and start harming other people, then I guess I would give up my cat. It would very painful… I know this is going to expose me internationally as a crazy cat lady, but he's, like, my child?"

Even if toxoplasmosis did lead to psychiatric problems, it seems unlikely to deter cat fans. As Ami points out, cats—toxoplasmosis carrying or not—tend to inspire a devotion in humans that borders on absolute mania. "I know three different people who are allergic to cats and they still have cats at home. One of them even has four cats."