What microorganism can make mice attracted to cats or make humans more likely to have car accidents or even develop a mental illness like schizophrenia? Host Guy Raz talks with infectious disease researcher Robert Yolken about Toxoplasma gondii and how it might affect human behavior.
GUY RAZ, host: If you or someone close to you has ever been pregnant, you've probably heard that pregnant women shouldn't change cat litter. That's because of a parasite some cats carry. It's called Toxoplasma gondii. Humans can become infected by handling cat litter. And if a pregnant woman becomes infected, toxoplasmosis can cause brain damage to the fetus.</s>GUY RAZ, host: Well now, a growing body of research is connecting toxoplasma to mental illness in adults - things like schizophrenia and bipolar disorders.</s>GUY RAZ, host: Dr. Robert Yolken, from Johns Hopkins Children's Center, has been studying the parasite's connection to mental illness. And he joins me from Baltimore.</s>GUY RAZ, host: Welcome to the program.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): Thank you very much.</s>GUY RAZ, host: First of all, how did cats themselves get infected with the parasite?</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): You know, I should say for toxoplasma's point of view, the world is divided into two parts. So it's cats or non-cats. Toxoplasma would like to be in a cat. The cat is where it can complete its life cycle, can undergo sexual reproduction. So that's really where it wants to be.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): Now toxoplasma gets into another animal, it's still alive, but it's not very happy. What I'm fond of saying is that it's kind of like a young person living in New Jersey. The person is alive but perhaps would rather be somewhere else...</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): ...so in New York City or Philadelphia or Washington. Somewhere...</s>GUY RAZ, host: Apologies to our listeners in New Jersey.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): I'm from New Jersey and my wife is, so I hope my fellow New Jerseyans won't mind my poking fun at my own state. But if you're a toxoplasma organism, you can't move so you have to change the motion of your host. And it appears that what toxoplasma does is, it actually changes the behavior of a host so it's more likely to get into a cat.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): And how does it - does this? Well, if a toxoplasma happens to be in a mouse or a rat, what it does is, it actually alters the behavior of the rodent in quite a specific way, to make it more likely to get eaten by a cat. And it does this by actually having the animal lose its fear of cats and actually get attracted to cats. So this is a quite amazing effect of a parasite on animal behavior.</s>GUY RAZ, host: Now, when humans are infected with this parasite, you have found a correlation between toxoplasmosis and changes in human behavior. Tell us what you found.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): Basically, we found that having toxoplasma raises the risk of schizophrenia about twofold, compared to the rest of the population. Toxoplasma probably functions through a pathway called dopamine. We know that dopamine is abnormal in schizophrenia, but the reason why it's abnormal is not really completely clear.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): Another behavior which appears to be altered is the individuals with toxoplasma appear to take more risks, in terms of driving a motor vehicle and also being a pedestrian.</s>GUY RAZ, host: Obviously, a lot of people listening to this who have cats - myself included - and small children might be a little bit terrified. What does this mean for people who own cats? I mean, should they keep their kids away from them?</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): No. I have cats. I have two - one that's ours, and one that's our daughter's, that we're cat-sitting for while she's in college. And I think cats are wonderful pets, and I would encourage people adopting cats. I think there are a number of things that one can do to lower the risk of toxoplasma.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): One is, if a cat is kept indoors, it's much, much less likely to get infected because it's not going out and eating rodents that might be outside. Secondly, I think that individuals who do have a litter box should be careful in terms of changing the litter and wearing gloves.</s>GUY RAZ, host: How would you know if your cat had it?</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): A veterinarian can generally do a test for a cat, and I'm told by my own veterinarian that that's not an uncommon request for people.</s>GUY RAZ, host: So do your cats have it?</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): My cats do not have it.</s>GUY RAZ, host: So you don't have it, probably.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): No. I am toxoplasma positive. So it's largely a silent infection. There are some symptoms - a headache, people not feeling well - but these usually resolve. So most people that have toxoplasma would not really have any reason for knowing it.</s>GUY RAZ, host: That's Robert Yolken. He's professor of pediatrics and a researcher at Johns Hopkins Children's Center in Baltimore.</s>GUY RAZ, host: Dr. Yolken, thanks so much.</s>Dr. ROBERT YOLKEN (Neurovirologist, Johns Hopkins Children's Center): Thank you very much.