If you get hot under the collar behind the wheel, it could be down to a brain parasite.

According to new research, adults who have intermittent explosive disorder (IED) - a psychiatric condition in which violent outbursts of anger and cursing erupt in response to apparently trivial irritations - are more likely to have been infected with toxoplasma gondii.

“The kind of triggers are usually social provocations,” said Dr Royce Lee, an author of the study from the University of Chicago. “In the workplace it could be some kind of interpersonal frustration, on the road it could be getting cut up.”

A common parasite, toxoplasma gondii reproduces within cats and is spread in their faeces. It can enter humans through the food chain in raw or undercooked meat, contaminated water or unwashed vegetables that have come into contact with the parasite.

It is thought that up to a third of the British population have been infected with toxoplasma gondii - a parasite that lurks in the tissues of the brain. While generally considered to be harmless, toxoplasmosis in pregnant women has been linked miscarriages, stillbirths and congenital defects in babies, and can cause serious problems in those with weakened immune systems.

While infection with the parasite in humans is often symptomless, its effects have attracted much attention - studies in humans have suggested that infection could be linked to schizophrenia and even increase the likelihood of road traffic accidents, while research in rats has found that infection with the parasite can remove their fear of cats.

Now scientists believe that the parasite could also linked to sudden outbursts of anger.

Writing in the Journal of Clinical Psychiatry, a team of US-based researchers revealed that they recruited 358 adults to explore whether their levels of impulsiveness and aggression were linked to infection with the parasite.

The participants were assessed for a range of traits including aggression and anxiety, and sorted into three groups: around a third had no signs of any psychiatric problems, a third were diagnosed with IED and the remainder were found to have a psychiatric or personality disorder other than IED, such as anxiety or depression.

The scientists then examined blood taken from the participants and screened it for evidence of past infection.

The results indicated that those who tested positive for a past exposure to toxoplasma gondii scored appreciably higher on scales of aggression than those who tested negative. What’s more, the scientists found that participants diagnosed with IED were more than twice as likely to have been exposed to the parasite than those with no evidence of a psychiatric disorder: nearly 22% of those diagnosed with IED were tested positive for signs of toxoplasma gondii, compared to 16.7% of those with other psychiatric disorders, and just 9% of healthy individuals. A similar trend was reflected in the participants’ levels of aggression.

“This paper is consistent with a number of publications that have appeared over the last 10 or 15 years showing a link between various mental and psychiatric conditions in humans and toxoplasma infection,” said Dr Richard Holliman, honorary consultant in medical microbiology at St George’s University Hospitals NHS Foundation Trust.

But he points out that the research only points to an association between IED and infection.

“That begs the question does the toxoplasma cause the behavioural pattern or does the behavioural pattern cause an individual to be more likely to catch toxoplasma infection,” he said. “It is a chicken and egg type argument. In humans we don’t have any strong data one way or the other.”

While the authors acknowledge that they have yet to show whether infection with toxoplasma gondii triggers the aggressive outbursts, they suggest a number of ways by which such an infection could affect the brain, including triggering activation of the immune system.

But Lee cautions against any knee-jerk reaction to the study. “We think it is too early for these kinds of results to affect any kind of human [action] - so people shouldn’t get rid of their cats,” he added.

“Toxoplasma positivity is very prevalent ... so in most cases it’s probably innocuous,” said Dr Glenn McConkey from the University of Leeds. “But in something where one has some psychological issues it might be compounding those issues.”