If you are prone to fits of impulsive rage, your cat may be responsible. Clawing the couch or knocking glasses off tables may do the trick, but a more likely mechanism is that it, or a long dead predecessor, infected you with toxoplasmosis.

Toxoplasma gondii, the parasite already linked to multiple mental health issues, has been connected to another. People infected by the parasite are twice as likely to experience unreasonable rage attacks (such as road rage) as those without, University of Chicago researchers have claimed.

From a cat’s perspective T. gondii is more symbiont than parasite. Cats spread it to rodents, whose behaviour changes to make them easier to catch. Our feline housemates/owners don’t really care if we get infected as well.

An estimated third of humans have picked up the parasite from cells deposited in cat faeces, although this is declining, in the U.S. at least, with improving hygiene. Aside from pregnant women or people with weakened immune systems, effects are usually subtle.

Epidemiological studies have provided evidence for personality changes and even increases in suicide. Last year cat ownership in childhood, a prime risk factor for infection, was linked to higher rates of schizophrenia, although the study did not demonstrate a causal connection. Moreover, being around cats is only one of the ways people catch toxoplasmosis. Eating undercooked meat and drinking untreated water containing the parasite are also known risk factors.

^{Yes cats, you should feel sorry for inflicting this on us, after all we do for you. smit/Shutterstock}

In the Journal of Clinical Psychiatry, Dr. Emil Coccaro has reported on 358 adults assessed for intermittent explosive disorder (IED) and T. gondii antibodies in the blood, as part of a wider study of aggression. Results found 110 had IED, and 138 other psychiatric disorders.

Only 9 percent of the study’s controls were infected, but this rose to 22 percent for those with IED, a statistically significant difference. However, no association was found between infection status and inward-directed aggression. Sixteen percent of the group were diagnosed with other conditions, but the sample size was too small to test differences between the multiple psychiatric disorders covered.

“We do not know if this relationship is causal, and not everyone that tests positive for toxoplasmosis will have aggression issues," Coccarro stressed in a statement. Indeed, the fact that so many of the control group carried the parasite indicates how common it is for those who are infected not to suffer.

"We don't yet 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,” added co-author Dr. Royce Lee “Our study signals the need for more research and more evidence in humans." The team hope to discover whether treatment of toxoplasmosis affects IED symptoms, defined as problematic outbursts of aggression disproportionate to the circumstances.

“Correlation is not causation, and this is definitely not a sign that people should get rid of their cats,” Lee said. Unless that is, it’s the cat’s misbehaviour, not its parasites, causing your rage.