Danish women infected with the toxoplasmosis parasite, a crescent-shaped freeloader that lives in rats and humans but can only reproduce in the guts of cats, were 1.5 times more likely to attempt suicide than their toxo-free counterparts, according to a new study published online in the Archives of General Psychiatry. Jezebel pounced, asking, “Are Cat Ladies More Likely To Commit Suicide?”
Toxoplasmosis is a simple organism that has evolved an elegant mind-bending mechanism for passing on its genes. When rats eat toxoplasmosis eggs in cat feces, they lose their fear of cats and become attracted to cat urine. These unwary rodents are then more likely to be eaten by cats, and the cycle begins again.
So how does it work? Rats instinctively fear the smell of cat pee, but the toxo parasite hijacks their brains to replace the normal hard-wired fear response with sexual arousal, especially in males. These rats don’t lose all fear. They are still afraid of most of the usual rat-scary stuff, like bright lights and dog urine. They just aren’t afraid of the smell of cat pee anymore. In fact, the males literally have a hard-on for the stuff. Of course, rats who are attracted to cat pee are more likely to get eaten by cats.
Humans, however, are unlikely to be eaten by cats, so where do we fit in?
When humans get infected—more often from rare meat and unwashed veggies than from cat boxes—the parasite settles into our muscles and brains and stays there, hidden from the immune system in protective cysts. About a third of people in developed countries are toxo carriers. The conventional medical wisdom is that toxo causes a brief mono-like illness in otherwise healthy people and becomes dormant thereafter.
However, a growing body of research suggests that toxo can subtly affect human behavior. Carriers are, then, more likely to try to kill themselves, and nearly three times more likely to die in car accidents.
Toxoplasmosis researcher Robert Sapolsky thinks toxoplasmosis might be affecting us the way it affects rats:
[Y]ou take a Toxo-infected rat and it does some dumb-ass thing that it should be innately skittish about, like going right up to cat smells. Maybe you take a Toxo-infected human and they start having a proclivity towards doing dumb-ass things that we should be innately averse to, like having your body hurdle through space at high G-forces.
Interestingly, the effects of toxoplasmosis vary by gender in rats and humans. Infected male rats become markedly more impulsive, females not as much. A series of small studies that compared personality tests in carriers and noncarriers found that men with toxoplasmosis were more “expedient, suspicious, jealous, and dogmatic,” whereas female carriers were warmer and more conscientious. It’s not clear how these findings square with the observation that women with toxo are more likely to harm themselves. Maybe toxo actually increases aggression and impulsivity in both genders, but women are more likely to turn these impulses inward.
Something to think about next time you’re tempted to order your pork loin super-rare. Then again, the fact that you’re even considering such a reckless act probably means you’re already infected.