Intermittent explosive disorder (IED) has been defined as “recurrent, impulsive, problematic outbursts of verbal or physical aggression that are disproportionate to the situations that trigger them.”
Toxoplasmosis is a common and generally harmless parasitic infection that is passed on through the feces of infected cats, contaminated water or undercooked meat.
It affects around 30% of all humans but is normally latent.
Research has revealed that the parasite is found in brain tissue, and it has been linked to a number of psychiatric conditions, including schizophrenia, bipolar disorder and suicidal behavior.
Researchers from the University of Chicago, led by Dr. Emil Coccaro, have been looking for more effective ways to diagnose and treat IED and impulsive aggression.
22% of subjects with IED tested positive for the parasite
In the current study, the authors evaluated 358 adult Americans for IED, personality disorder, depression and other psychiatric disorders and gave them scores for traits such as anger, aggression and impulsivity. They also screened for toxoplasmosis using blood tests.
Fast facts about toxoplasmosis
- Around 60 million Americans are thought to have toxoplasmosis
- If a woman catches it just before or during pregnancy, it can be dangerous for the baby
- For those with a weakened immune system, there are medications to treat it.
They then classified the participants into three groups: approximately one third had IED, one third were healthy controls with no psychiatric history, and one third had received a diagnosis for a psychiatric disorder but not IED.
The purpose of the last group was to enable the team to distinguish IED from other psychiatric factors.
Findings showed that 22% of those with IED tested positive for toxoplasmosis exposure, compared with 9% of the healthy control group and 16% of the psychiatric control group.
The psychiatric group and the healthy group had similar scores for aggression and impulsivity, but the group with IED scored far higher on both counts than either of the other two groups.
An association emerged between toxoplasmosis and impulsivity. However, when the team adjusted for aggression scores, this association became non-significant, indicating a strong correlation between toxoplasmosis and aggression.
The authors point out that the findings do not mean that toxoplasmosis causes IED, or that people with cats are more likely to have the condition. It simply reveals a relationship.
The cat is not to blame
Coauthor Dr. Royce Lee, associate professor of psychiatry and behavioral neuroscience at the University of Chicago, says:
“This is definitely not a sign that people should get rid of their cats. We don’t 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.”
The researchers emphasize the need for further research to confirm the findings and to find out if there is a causative relationship.
Senior study author Dr. Emil Coccaro, Ellen. C. Manning Professor and Chair of Psychiatry and Behavioral Neuroscience at the University of Chicago, says:
“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. However, we do not know if this relationship is causal, and not everyone that tests positive for toxoplasmosis will have aggression issues.”
The team is already looking further into the link between toxoplasmosis, aggression and IED, in the hope of ultimately finding new ways to diagnose or treat “rage” disorder, possibly by tackling the latent infection first.
Medical News Today has previously reported on research linking toxoplasmosis with schizophrenia.