A parasite lurking in cat litter boxes can cause a rare disorder that is characterized by random and extreme outbursts of rage, a new study is reporting.
For this study, the researchers wanted to determine why some people are more likely than others to have intermittent explosive disorder (IED). People with IED might react aggressively, impulsively or violently in situations that might not warrant such a reaction.
The researchers recruited 358 adult participants who were being evaluated for psychiatric disorders such as IED and depression. The participants were graded on specific traits, such as aggression, impulsivity and anger. Overall, about one-third of the people had IED.
The researchers found that people from the IED group were two times more likely to have a positive test for the parasite, toxoplasma gondii, which is most commonly found in the feces of infected cats, than people who did not have IED or any other psychiatric conditions. The percentages of people with positive blood tests were 22 percent in the IED group, 9 percent in the healthy control group and 16 percent in the group of people with psychiatric disorders that did not include IED.
In terms of aggression and impulsivity levels, people with IED had the highest scores whereas the scores in the other two groups were pretty similar. Overall, the researchers found that people who were infected by toxoplasma gondii were also more likely to have higher scores for anger and aggression.
"Our work suggests that latent infection with the toxoplasma gondii parasite may change brain chemistry in a fashion that increases the risk of aggressive behavior," said Ellen C. Manning Professor and Chair of Psychiatry and Behavioral Neuroscience at the University of Chicago Emil Coccaro. "However, we do not know if this relationship is causal, and not everyone that tests positive for toxoplasmosis will have aggression issues."
"Correlation is not causation, and this is definitely not a sign that people should get rid of their cats," added Royce Lee, an associate professor of psychiatry and behavioral neuroscience at the University of Chicago and a co-author of the study, which was published in the Journal of Clinical Psychiatry. "We don't yet understand the mechanisms involved - it could be an increased inflammatory response, direct brain modulation by the parasite or even reverse causation where aggressive individuals tend to have more cats or eat more undercooked meat. Our study signals the need for more research and more evidence in humans."
Even though the researchers did not find that the parasite can cause IED, the findings are still important - especially since the parasite is very common. About 30 percent of all humans have the parasite.
