Theories that a cat parasite can alter the minds of humans — triggering sexual desire, testosterone levels, recklessness, suicidal urges, and now even schizophrenia — are gaining momentum. A fascinating Atlantic profile of the Czech scientist leading the theories about Toxoplasma documents the mind-control hypotheses as they've grown from crackpot fringe science to heavily studied phenomena. Once seen as mainly a threat to pregnant women (it can cause brain damage in fetuses), Toxoplasma then became known as "zombie rat parasite," then "crazy cat lady parasite," and now it's gaining a reputation as the "all kinds of scary shit parasite." NPR, Radiolab, and Carl Zimmer's parasite chronicling have made it a star.
Here's the short version of what the organism lovingly known as Toxo does: the protozoa lives in and can only reproduce in the guts of cats. The single-celled parasite spreads by sending cells out of the cat by way of the rear, and the cells then get into other animals via poop, dust, dirt, cat litter, standard parasite stuff. But here's where it gets weird. Toxoplasma needs to get back into a cat to reproduce. So the cells have a rare talent for getting back into cats via other animals. The parasites work their way into the brains of rats and rewire brain functions that affect fear and sexual attraction. In short, Toxo can make rats attracted to the smell of cat pee, luring its unknowing host into the jaws of its own predator, and taking the parasite home to the cat gut.
That would be creepy enough. But researchers have also found that, because Toxo can be spread sexually from rat to rat, it can somehow make male rats sexier to other uninfected female rats. Rats have sex, the parasite spreads cells out even more, more rats run to more cats, Toxo wins again.
It gets worse though, as scientists like Jaroslav Flegr have been conducting increasing amounts of research on how Toxoplasma can affect not just rats, but humans. The results aren't devastating, but they are definitely unsettling. In developing countries, it infects 95% of the human population, and in the U.S. it affects around 10%. It's long been considered harmless and lies dormant in the brain after infection, but exactly how dormant has been up for debate.
One theory is that people who have Toxoplasmosis have an unusual affinity for cats, or at least a lack of distaste for the smell of cat urine. The parasite was targeted as the source of the crazy cat lady. But the profile of Flegr, by Kathleen McAuliffe in the current issue of The Atlantic, cracks open a whole new vault of brain problems we can blame on Toxoplasmosis. Flegr has researched the possibility that it can make human hosts less fearful, and more reckless behind the wheel of a car. He thinks it has a similar effect on suicidal tendencies. And last but not least, its ability to control dopamine levels could be a factor in triggering latent schizophrenia in those genetically predisposed.
It sounds like sci-fi, with a foreign entity settling into the folds of our brains and controlling our actions and personalities. But when you think about rabies, which has the ability to fill its hosts with a raging impulse to bite and scratch, combined with a deadly fear of water that stops them from flushing the virus, it's not so crazy. And considering our bodies are each a bustling universe of microorganisms, who knows what's in there pushing buttons.
Photo: my cat Knives, whom I love unconditionally.