A previous brain infection from toxoplasmosis, an infection from a parasite found in cat feces, may be to blame for uncontrollable bouts of anger, such as those displayed in a road rage.
New research from the University of Chicago found that psychiatric disorder patients with such recurrent, extreme anger were over twice as likely to have been exposed to the parasite compared to their healthy counterparts.
The study involving 358 adults linked infection with the Toxoplasma gondii to altered brain chemistry leading to intense emotional outbursts — a disorder called Intermittent Explosive Disorder (IED) — and greater aggression.
"However, we do not know if this relationship is causal, and not everyone that tests positive for toxoplasmosis will have aggression issues," says senior study author and psychiatry professor Dr. Emil Coccaro, calling for more research in this area.
IED is characterized by verbal or physical aggression and believed to afflict up to 16 million Americans — more than the those diagnosed with bipolar disorder and schizophrenia combined.
Toxoplasmosis, a highly common parasitic infection, is communicated via cat feces, contaminated water, or undercooked meat. The infection, while known to be relatively harmless and carried by about 30 percent of all people, resides in brain tissue and may results in a number of psychiatric conditions such as schizophrenia and suicidal tendencies.
The team evaluated the subjects for IED, depression, personality disorder, as well as other psychiatric issues, and analyzed their scores on traits like anger and impulsivity. The findings categorized them into three: the IED group, a group diagnosed with psychiatric disorders other than IED, and the healthy controls.
The IED group emerged as over twice as likely to surface with toxoplasmosis exposure versus the healthy controls. About 16 percent of the psychiatric group were positive for toxoplasmosis, but retained similar aggression and impulsivity scores to the healthy controls — traits where the IED group scored significantly higher than the two other groups.
The authors, however, reminded that the results showed correlation instead of causation — and that people shouldn't be getting rid of their cats out of fear. The underlying mechanism remains unclear and could involve factors such as increased inflammation, they explained.
Dr. Coccaro highlighted inflammation as a leading theory, explaining that the infection triggers antibody production, which then initiates the body's natural inflammatory action to fight infections.
After ingestion, Toxoplasma can go to the brain, where it can hide inside cells and induce an inflammatory response that damages the nerve cells during the immune system's attempt to kill the parasite.
The team is investigating the matter more closely and looking at whether drug therapy for toxoplasmosis could reduce aggressive behavior.
The findings were published March 23 in the Journal of Clinical Psychiatry.
Photo: Moyan Brenn | Flickr