Toxoplasmosis linked to human anger

Cuddling a cat can be good for the soul, but caring for a cat could lead to the opposite effect. Indeed, a parasite found in the feces of infected cats can trigger explosive emotions in humans a new study suggests.

Researchers at the University of Chicago found that toxoplasmosis is associated with intermittent explosive disorder and increased aggression in humans.

The study was published in the Journal of Clinical Psychiatry on March 23.

The researchers examined possible connections to toxoplasmosis, transmitted through the feces of infected cats, undercooked meat, or contaminated water. Typically latent and harmless for healthy adults, toxoplasmosis is known to reside in brain tissue, and has been linked to several psychiatric diseases, including schizophrenia, bipolar disorder, and suicidal behavior.

The research team recruited 358 adult subjects from the United States who were evaluated for Intermittent Explosive Disorder (IED), personality disorder, depression, and other psychiatric disorders. Study participants were also scored on traits including anger, aggression, and impulsivity. Participants fell into one of three groups.

Roughly one third of the participants had IED. One third were healthy controls with no psychiatric history. The remaining third were individuals diagnosed with some psychiatric disorder, but not IED. This last group served as a control to distinguish IED from possible confounding psychiatric factors.

“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 senior study author Emil Coccaro, MD, Ellen. C. Manning Professor and Chair of Psychiatry and Behavioral Neuroscience at the University of Chicago.

“However, we do not know if this relationship is causal, and not everyone that tests positive for toxoplasmosis will have aggression issues,” Coccaro said.

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