Chicago, Mar 26: A common brain parasite that is transmitted through faeces of infected cats, undercooked meat or contaminated water may increase the risk of aggressive behaviour such as road rage in infected people, a new study has claimed.
In the study involving 358 adult subjects, researchers from the University of Chicago found that toxoplasmosis, a relatively harmless parasitic infection carried by about 30 per cent of all humans, was linked to intermittent explosive disorder (IED) and increased aggression.
"Our work suggests that latent infection with the toxoplasma gondii parasite may change brain chemistry in a fashion that increases the risk of aggressive behaviour," said senior study author Emil Coccaro, professor 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. IED is defined as recurrent, impulsive, problematic outbursts of verbal or physical aggression that are disproportionate to the situations that trigger them.
Researchers examined possible connections to toxoplasmosis, an extremely common parasitic infection. Transmitted through the faeces 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 behaviour.
The research team recruited 358 adult subjects from the US, 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.
The research team found that IED-diagnosed group was more than twice as likely to test positive for toxoplasmosis exposure (22 per cent) as measured by a blood test, compared to the healthy control group (9 per cent).
Around 16 per cent of the psychiatric control group tested positive for toxoplasmosis, but had similar aggression and impulsivity scores to the healthy control group. Across all study subjects, toxoplasmosis-positive people scored significantly higher on scores of anger and aggression. This finding suggests toxoplasmosis and aggression are most strongly correlated.
However, the researchers caution that the study results do not address whether toxoplasmosis infection may cause increased aggression or IED. The study was published in the Journal of Clinical Psychiatry.