Individuals diagnosed with intermittent explosive disorder and heightened aggression are more than twice as likely to have been exposed to the relatively common parasite Toxoplasma gondii than individuals with no psychiatric diagnosis, according to a study published in The Journal of Clinical Psychiatry and covered by Science Daily.
For the study, researchers from the University of Chicago recruited 358 physically healthy participants who either reported psychosocial difficulty related to psychiatric and/or personality disorders, or displayed little evidence of psychopathology. The participants were analyzed and diagnoses were made in accordance with the DMS-5 criteria — 110 subjects were not diagnosed with a disorder providing the experiment with its healthy control group, 138 were diagnosed with some psychiatric disorder but not intermittent explosive disorder and the remaining 110 participants met the criteria for a lifetime diagnosis of IED.
Blood tests indicated that 22 percent of the IED-diagnosed patients tested positive for toxoplasmosis. Approximately 16 percent of the group with alternate psychiatric disorders tested positive, while only 9 percent of the healthy control group issued positive tests for exposure to the parasite.
"It will take experimental studies to see if treating a latent toxoplasmosis infection with medication reduces aggressiveness...if we can learn more, it could provide rationale to treat IED in toxoplasmosis-positive patients by first treating the latent infection," senior study author Emil Coccaro, MD, a professor at the University of Chicago, said in Science Daily.
Exposure to Toxoplasma gondii transpires primarily through oral transmission and occurs in an estimated 30 percent of people. The parasite can often be found in contaminated cat feces.
"Correlation is not causation, and this is definitely not a sign that people should get rid of their cats," study co-author Royce Lee, MD, said in Science Daily. "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."
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