What if your cat Fluffy had a microscopic parasite, which you ingested one day when you absentmindedly stuck your finger in your mouth after petting her? What if that parasite migrated throughout your body and took up residence inside brain cells, and started manufacturing an enzyme that affected the amount of dopamine in your brain, causing changes in your mood, sociability, attention, and motivation?

That is the subject of an article by Kathleen McAuliffe in the March issue of The Atlantic magazine profiling a Czech scientist named Jaroslav Flegr. He contends that a single-celled protozoan called Toxoplasma Gondii may be tweaking the connections between our neurons, changing our response to frightening situations, our trust in others, and our preference for certain scents. Flegr also believes that the protozoan may be a main cause of psychiatric disorders such as schizophrenia.

Toxoplasma Gondii has been around for millions of years, as part of a life cycle that revolves around rodents and cats. A cat will eat an infected mouse, and the parasites will infect the lining of the cat’s small intestine, and undergo sexual reproduction. (how romantic!)  Then, a hardy, thick walled spore is excreted by the cat, where it can be ingested by rodents, completing the cycle. Unfortunately, it can also be ingested by humans or other animals by consuming unwashed vegetables, drinking contaminated water, or otherwise coming in contact with cat feces. It has been estimated that up to half the world’s population may be infected with Toxoplasma.

The parasite causes a disease in humans called Toxoplasmosis. Pregnant women have long been warned not to clean cat boxes, due to the danger of being infected and harming the fetus. An infection can sometimes lead to brain swelling or eye damage, or even death for those with compromised immune systems. But for most people, an infection just causes some temporary flu-like symptoms, after which T. Gondii enters a latent phase, retreating to cysts inside muscle and nerve cells. It has always been thought that the parasite was harmless in this state, but new research is calling that into question.

The really interesting thing to me is the way that T. Gondii is apparently able to change rodent behavior in order to make them more likely to be eaten by cats, which is the only way the parasite can have a booty call. Studies have shown that infected rat’s brains are rewired to turn their innate aversion to cats into an attraction, luring it into the jaws of its number one predator by tamping down its fear of felines and even making cat urine smell good to them.

The problem for humans is that, although we may not like to think of it this way, our brains are not that different, biologically speaking, from rat brains. Jaroslav Flegr believes that the T. Gondii parasites are affecting our brains in much the same way they do the rats, in a case of mistaken identity.

So, do you really love your cat? Or is that just the parasites talking?