Toxoplasma (“Toxo”) is a parasite that changes mammalian behavior. According to Robert Sapolsky
When you look at normal rats, and expose them to cat urine, cat pheromones, exactly as you would expect, they have a stress response: their stress hormone levels go up, and they activate this classical fear circuitry in the brain. Now you take Toxo-infected rats, right around the time when they start liking the smell of cat urine, you expose them to cat pheromones, and you don’t see the stress hormone release. What you see is that the fear circuit doesn’t activate normally, and instead the sexual arousal activates some. In other words, Toxo knows how to hijack the sexual reward pathway. And you get males infected with Toxo and expose them to a lot of the cat pheromones, and their testes get bigger. Somehow, this damn parasite knows how to make cat urine smell sexually arousing to rodents, and they go and check it out. Totally amazing.
And suddenly, one of them jumps up, flooded with 40-year-old memories, and says, “I just remembered back when I was a resident, I was doing a surgical transplant rotation. And there was an older surgeon, who said, if you ever get organs from a motorcycle accident death, check the organs for Toxo. I don’t know why, but you find a lot of Toxo.” And you could see this guy was having a rush of nostalgic memories from back when he was 25 and all because he was being told this weird factoid … ooh, people who die in motorcycle accidents seem to have high rates of Toxo. Utterly bizarre.
What is the bottom line on this? Well, it depends; if you want to overcome some of your inhibitions, Toxo might be a very good thing to have in your system. Not surprisingly, ever since we started studying Toxo in my lab, every lab meeting we sit around speculating about which people in the lab are Toxo-infected, and that might have something to do with one’s level of recklessness. Who knows? It’s very interesting stuff, though.
You want to know something utterly terrifying? Here’s something terrifying and not surprising. Folks who know about Toxo and its affect on behavior are in the U.S. military. They’re interested in Toxo. They’re officially intrigued. And I would think they would be intrigued, studying a parasite that makes mammals perhaps do things that everything in their fiber normally tells them not to because it’s dangerous and ridiculous and stupid and don’t do it. But suddenly with this parasite on board, the mammal is a little bit more likely you go and do it. Who knows? But they are aware of Toxo.
Toxoplasma, a parasite that makes cat urine smell sexy to rats, makes humans more likely to crash their motorcycles, and might be just what you need to overcome your mousy ways. Unless you’re pregnant …
If you’re ever pregnant, if you’re ever around anyone who’s pregnant, you know you immediately get skittish about cat feces, cat bedding, cat everything, because it could carry Toxo. And you do not want to get Toxoplasma into a fetal nervous system. It’s a disaster.
Update: A recent article from The Economist.