How Cats Can Control Us

James Hamblin digs into what’s really going on with Toxoplasmosis gondii, a parasite spread by cats, and its effect on the human mind:

Toxo has been all over the news in recent years, since it became known that the parasite manipulates people’s behavior. Maybe most interestingly and notoriously, it seems to make men more introverted, suspicious, unattractive to women, and oblivious to the way others see them. Infected women, inversely, have been shown to be more outgoing, trusting, sexually adventurous, attractive to men, and image-conscious. Infected men tend to break more rules than their uninfected peers, and infected women tend to pay them more heed. Infected men and women are 2.5 times more likely to have traffic accidents, more likely to develop schizophrenia, and more likely to engage in self-directed violence. …

Tyrosine hydroxylase is involved in production of the normally-occurring neurotransmitter dopamine. More of the enzyme means more dopamine. This changes behavior of mice, and Webster and Stock extrapolate, people. That explanation means that Toxo infection increases dopamine in our brains. It’s different, though, from the kind of dopamine boost we usually hear about in pop neuroscience likened to a runners’ high. “When you’re doing something rewarding—drinking a cup of coffee, talking to a friend, having sex, whatever—you have a boost of dopamine specifically in the limbic regions of your brain,” she said. “But Toxoplasmosis spreads all over your brain, infecting dopamine-producing neurons in many pathways. Given that the dopamine-based system is complex and influences many aspects of cognition and behavior, there is a plethora of effects that might be observed.”

How to avoid infection:

Indoor cats pose no threat, he says, because they don’t carry the parasite. As for outdoor cats, they shed the parasite for only three weeks of their life, typically when they’re young and have just begun hunting. During that brief period, Flegr simply recommends taking care to keep kitchen counters and tables wiped clean. (He practices what he preaches: he and his wife have two school-age children, and two outdoor cats that have free roam of their home.) Much more important for preventing exposure, he says, is to scrub vegetables thoroughly and avoid drinking water that has not been properly purified, especially in the developing world, where infection rates can reach 95 percent in some places. Also, he advises eating meat on the well-done side—or, if that’s not to your taste, freezing it before cooking, to kill the cysts.