That 'Cat-Litter Parasite' Might Make You Madder Than You Know

By Sophie Lucido Johnson in News on Mar 25, 2016 8:58PM

Toxoplasma gondii, the "cat litter parasite" that has perhaps spawned more memes than any other, might be responsible for yet another human affliction: rage. Scientists at the University of Chicago published a study in the Journal of Clinical Psychology this week stating that their research suggests the parasite may change brain chemistry to increase the risk of aggressiveness in humans.

The parasite has been linked to all kinds of crazy cat-person behavior: There's research that says it causes people to get into more car accidents, have children who are more likely to be prone to schizophrenia, and experience wild mood swings. Toxoplasma gondii — which causes an infection called toxoplasmosis — is especially scary because it thrives inside cats and is easily transmittable; 30 to 50 percent of the world human population is estimated to have it. (Symptoms of the parasite usually go unseen, or remain dormant for years.)

The University of Chicago's study tested 358 adults for Intermittent Explosive Disorder (IED), personality disorders, depression, and other psychiatric disorders. The aim was to determine if there was a likelihood that toxoplasmic gondii might trigger IED—the disorder associated with aggression, anger, and road rage. Researches sorted participants into three groups: A third had IED, a third had some psychiatric disorder (not IED), and the remaining third served as the healthy controls. Participants were then tested for exposure to toxoplasma gondii, in order to find a possible correlation.

The results showed that participants with exposure to toxoplasma gondii were significantly more likely to have high scores on an aggressiveness scale than participants who were unexposed. Furthermore, participants with IED were more than twice as likely to have exposure to the parasite than the control group. Researchers found that while just 9 percent of the healthy individuals showed signs of toxoplasma gondii, nearly 22 percent of individuals with IED showed the same signs.

The trouble with the research is that it only indicates some association between IED and toxoplasma gondii — not any sort of proof of cause and effect. In other words, the question of whether exposure to the parasite makes a person more likely to develop IED, or if IED is more likely to cause a person to be exposed to the parasite, is still unanswered. The next step will be to conduct experiments to see if medically treating the toxoplasmosis infection will reduce aggressiveness. If so, there may be hope on the horizon for those who habitually lose their cool in public.