Intermittent explosive disorder (IED) is defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, as recurrent, impulsive, problematic outbursts of verbal or physical aggression that are disproportionate to the situations that trigger them. IED is thought to affect as many as 16 million Americans, more than bipolar disorder and schizophrenia combined. . . .From here. The source for the quoted article is Emil F. Coccaro, et al., "Toxoplasma gondii Infection." The Journal of Clinical Psychiatry (2016).
Coccaro and his colleagues examined possible connections [of IED] to toxoplasmosis, an extremely common parasitic infection. Transmitted through the feces of infected cats, undercooked meat or contaminated water, toxoplasmosis is typically latent and harmless for healthy adults. However, it 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 U.S., who were evaluated for 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 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.
The research team found that IED-diagnosed group was more than twice as likely to test positive for toxoplasmosis exposure (22 percent) as measured by a blood test, compared to the healthy control group (9 percent). Around 16 percent of the psychiatric control group tested positive for toxoplasmosis, but had similar aggression and impulsivity scores to the healthy control group. IED-diagnosed subjects scored much higher on both measures than either control group.
Across all study subjects, toxoplasmosis-positive individuals scored significantly higher on scores of anger and aggression. The team noted a link between toxoplasmosis and increased impulsivity, but when adjusted for aggression scores, this link became non-significant.
Another recent post on the effect of this infection on personality is here. A previous post linking the infection to suicide is here.