People prone to angry outbursts are more than twice as likely to be infected with a common parasite called Toxoplasma gondii, which is often spread through cat feces. So report researchers in the Journal of Clinical Psychiatry, who looked for circulating antibodies to the parasite in 358 adults with intermittent explosive disorder (IED), non-IED psychiatric disorders (psychiatric controls), or no evidence of any psychiatric diagnosis (healthy controls). They found the parasite in just 9% of those without IED but 22% of those with it. Toxoplasmosis has been linked to schizophrenia, bipolar disorder, impulsiveness, and suicidal behavior, reports the Telegraph, but even so this finding surprised researchers.
"We don't yet understand the mechanisms involved," coauthor Dr. Royce Lee of the University of Chicago tells Live Science. "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." Indeed, the study establishes an association but not causation, and while the parasite can cause severe neurological problems and death in infants infected through pregnant mothers, it tends to cause far fewer problems in most of the 20% of Americans who've been infected by it. Researchers may next look for the parasite in the brains (instead of just bodies) of those with IED, or try treating IED patients for the infection to see if symptoms disappear. (Check out the broader range of issues the parasite is linked to in humans.)