Your Cat is Literally Making You Crazy

See that guy up there? That’s my guy! He’s probably thinking about how much he loves me and wants to destroy me. And according to a scientist based in the Czech Republic, he’s also probably infected me with parasites that have re-routed neural responses in my brain.

He’s literally making me crazy.

An article in the March 2012 issue of Atlantic Magazine profiled the research of Jaroslav Flegr, a Czech Republic scientist who has been researching the effect that the parasitic protozoa Toxoplasma gondii has, or doesn’t have, on adults infected by the microbe.

For those who have cats and pregnant friends, T. gondii is a familiar term as the parasite commonly occurs in feline waste and has a deleterious effect on a growing fetus, with the disease caused by the parasite in some cases resulting in severe brain damage or death.

The parasite reproduces in cats but commonly hosts itself in mice, rats, humans, and birds. Although T. gondii can cause behavioral changes in smaller mammals (rats actually become oddly cat friendly), it has never seemed to cause a demonstrative effect in human behavior, and was assumed to be dormant while inside the body.

Causing behavioral changes in their hosts is a favorite pasttime for certain parasites. Flatworms hijack ant brains and turn them into easy prey so the flatworm can be ingested by larger animals. The orb spider is commonly set upon by the Polysphincta gutfreundi wasp, which infects the spider and forces it to care for the wasp’s young. Other wasps are set upon by X. vesparum, which force the wasp to withdraw from the hive and mate only with other wasps infected by the same parasite. If you’re an insect, parasites are the worst.

toxoplasma gondii cats crazy

Hi, I'm Toxoplasma gondii. Pet the kitty. Do it. Pet the kitty.

The more developed and complex the brain, the harder the foothold for a parasite, but it isn’t unheard of for humans to succumb to microbes of that nature. The entire reason rabies causes frothing of the mouth is because the parasite that causes the disease travels in saliva.

Flegr’s reasons for looking more intently at T. gondii were personal and subjective in nature—his youth was characterized by reckless behavior and a lack of understanding as to why it was reckless, and he saw a parallel in smaller mammals and their behavior while infected with T. gondii. Such correlations aren’t science, though, so Flegr began to devise tests for his theory.

T. gondii can live anywhere but needs to return to a cat in order to reproduce, so it manipulates its host into behaviors that will lead to an encounter. In small mammals, this results in a more hyperactive manner (cats are attracted to things that move suddenly and quickly), and a self-destructive lack of fear of predators and environments that cats are found in. Flegr tested infected and non-infected humans in scenarios that demonstrated these qualities, and found these behaviors manifesting in infected humans. Further:

Flegr was especially surprised to learn, though, that the protozoan appeared to cause many sex-specific changes in personality. Compared with uninfected men, males who had the parasite were more introverted, suspicious, oblivious to other people’s opinions of them, and inclined to disregard rules. Infected women, on the other hand, presented in exactly the opposite way: they were more outgoing, trusting, image-conscious, and rule-abiding than uninfected women.

The findings were so bizarre that Flegr initially assumed his data must be flawed. So he tested other groups—civilian and military populations. Again, the same results.

Although Flegr had a good starting point, the idea was still a bit too touchy to present in full. (I’d like to think that this is because cats are awesome, but I am clearly biased.) Flegr didn’t have to wait long, though.

Two studies in 2011 replicated Flegr’s research and found a link between T. gondii-infected humans and traffic accidents. The hyperactivity led to a loss of focus and slower reaction times. (Read the Atlantic article for a more detailed rundown of his research and other findings.)

Another study from Michigan State University in the summer of 2012 linked T. gondii with depression and suicide attempts. The study found that people suffering from depression were seven times more likely to commit suicide if they were infected by the parasite. The lack of fear caused by the parasite seemed to be manifesting as a diminishing sense of self-preservation in humans.

While the presence of Toxoplasma gondii in the human brain doesn’t lead to the exact same effects that it does in animals (rats actually become attracted to cat urine and I can provide AMPLE anecdotal data that cat urine is repellent and obnoxious as hell) there is one conclusion that I find inescapable:

My cat has infected me with a parasite that rebuilt my brain so I will love it more.

And I do.

And I am happy here.

Chris Lough is the production manager of and is, in fact, a cat lover and does, in fact, love to run and, sadly, can’t hug every cat.

Photo by Elizabeth Kies used with permission.


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