Why I’ll Never Own a Cat (And Why You Shouldn’t Either)

Unless you like brain parasites that cause subtle sex-specific changes in your personality.

Jon Miltimore | December 20, 2016

Unless you like brain parasites that cause subtle sex-specific changes in your personality.

Last summer, a few neighbor children came running up to our house. They had found a litter of kittens under their deck. My 5-year-old daughter was out the door so fast I didn’t have the opportunity to shout, “Stop! Brain parasites!”

I’ve been deathly afraid of cats for five years now. It all stems from a 2012 article in The Atlantic: “How Your Cat Is Making You Crazy.”

Now, I do not suffer from Ailurophobia. This condition describes an irrational fear of cats (from the Greek αἴλουρος (ailouros), "cat" and φόβος (phóbos), "fear"). My fear is hardly irrational. Any person who reads Kathleen McAuliffe's article on cats, rats, and brain parasites and is not afraid of them is irrational, in my humble opinion.

Let me explain. Jaroslav Flegr is a 58-year-old Czech scientist, a parasitologist to be precise. He has spent decades studying a particularly nasty parasite—Toxoplasma gondii (T. gondii for short). The parasite is excreted by cats, which is why pregnant women are instructed to stay away from cat litter.

This is nothing new. Doctors since the 1920s, McAuliffe notes, have recognized that a woman who becomes infected with the parasite during pregnancy can transmit it to the fetus, which can cause brain damage and death. But Flegr, beginning in the early 1990s, became convinced T. gondii was affecting him—and millions of other humans around the world—in profound ways.  

Here is how it works, via McAuliffe:

After an infected cat defecates, Flegr learned, the parasite is typically picked up from the soil by scavenging or grazing animals—notably rodents, pigs, and cattle—all of which then harbor it in their brain and other body tissues. Humans, on the other hand, are exposed not only by coming into contact with litter boxes, but also, he found, by drinking water contaminated with cat feces, eating unwashed vegetables, or, especially in Europe, by consuming raw or undercooked meat. Hence the French, according to Flegr, with their love of steak prepared saignant—literally, “bleeding”—can have infection rates as high as 55 percent. (Americans will be happy to hear that the parasite resides in far fewer of them, though a still substantial portion: 10 to 20 percent.)

This is disturbing, but what is even more so is how the parasite works itself back into its original host.

Once inside an animal or human host, the parasite then needs to get back into the cat, the only place where it can sexually reproduce—and this is when, Flegr believed, behavioral manipulation might come into play.

For years researchers have noticed that rats infected with T. gondii behave strangely. They are less afraid of predators and more prone to chase after objects, symptoms that make them prime targets to become cat food. Now, there is no conceivable way in which the parasite could work to make humans cat food. But Flegr found that humans infected with T. gondii have symptoms that affect them in weird ways. His native country was a fertile ground for test subjects, it turned out; some 40 percent of Czechs had the latent form of the parasite. So he started running tests. 

He began by giving them and their parasite-free peers standardized personality tests—an inexpensive, if somewhat crude, method of measuring differences between the groups. In addition, he used a computer-based test to assess the reaction times of participants, who were instructed to press a button as soon as a white square popped up anywhere against the dark background of the monitor.

What did he find? Numerous sex-specific changes in test subjects infected with T. gondii. Men were less rule-abiding, more suspicious and introverted. They more often dressed like slobs and were more likely to be oblivious to what people thought about them. Women, on the other hand, became more social. More trusting and rule-abiding. More (uh) into brand clothing.

Do the findings sound absurd? Absolutely. Flegr would agree; he was so puzzled by the results he thought his own data must have been flawed. He ran a second test; it checked out.

It's difficult to believe the comforting idea that Flegr is just a quack. Numerous other highly-credentialed scientists cited in the article claim Flegr’s methodology is sound.

There is reason to believe the parasite is linked to both schizophrenia and suicide, readers are told, and is responsible for tens of thousands of car crashes annually, the result of slower brain motor function in parasite-afflicted drivers. (Parasite-infected subjects were about 250 percent more likely to be in auto collisions than uninfected subjects, both studies found.)

Learning that a brain parasite can make a mammal become attracted to its own prey is creepy. Learning that it affects millions of people in subtle ways they cannot even perceive is even creepier. (Women, for example, appear to find men infected with the parasite more attractive.)

Read the entire article to get the context and the caveats (i.e. the parasite allegedly poses no threat to indoor cats), but I’ll offer a guarantee: anyone who reads the entire article will find themselves wondering if he or she is infected with T. gondii. (Don't worry: You can take a test to find out.) 

And I promise this: readers will wince when the neighbor kids run over telling you a stray cat has given birth to kittens under their deck.


Jon Miltimore is senior editor of Intellectual Takeout. Follow him on Facebook