Scientists revisit link between cats and road rage
Study shines new light on explosive earlier findings
Pity the cats. They’re always getting blamed for something.
In the 13th century, Pope Gregory IX declared them evil and worthy of death, which led to their widespread killing. More recently, they’ve been accused of killing off birds. Now this: Cats are linked to road rage.
That’s been one common takeaway from a study, published last week in the Journal of Clinical Psychiatry, that is the latest to link the common parasitic infection toxoplasmosis to behaviour changes or psychiatric disorders in humans. This one found that people with intermittent explosive disorder — who have recurrent outbursts of extreme anger, like road rage — are more than twice as likely as healthy people with no psychiatric disorders to have been exposed to Toxoplasma gondii as the parasite is known.
T. gondii’s survival depends on cats, because it reproduces only in cat intestines and is spread via feline feces.
About one-third of people worldwide have been infected with T. gondii, though the infection rate varies widely from country to country. The figure is as high as about 75 per cent in Costa Rica; in the U. S., it’s believed to be 10 to 20 per cent. After being deposited into the world by cat poop, the parasite spreads and people can get it from that excrement, but also from undercooked meat or contaminated water.
It can cause brain damage or even death to fetuses, which is why pregnant women are advised not to clean litter boxes, and are treated with antibiotics if they test positive for toxoplasmosis. But most healthy people who are infected feel a bit flu-like or show no symptoms, even though the parasite can remain latent in brain tissue. So, for a long time, science didn’t worry much about it.
In recent decades, scientists have been probing the connections between T. gondii and psychiatric disorders and behaviour changes in humans, and they’ve found several. Studies have linked infection to schizophrenia, suicide attempts and traffic accidents. One 2015 study found that children with latent infections had poorer reading skills and reduced memory.
The cat connection sailed into public view in 2012, when the Atlantic published an article headlined “How your cat is making you crazy.” It focused on a Czech evolutionary biologist named Jaroslav Flegr who blamed T. gondii for causing untold trouble.
But in humans, the links between toxoplasmosis and psychiatric diseases or behaviour changes so far are just that — correlations.
Last month, cat owners breathed a sigh of relief with the release of another study, published in PLoSOne, that found “little evidence” of links between T. gondii and schizophrenia, depression, suicidal behaviour, criminality or effects on personality or memory.
The authors said maybe previous links have been “exaggerated.” There’s no reason to shun cats, said Royce Lee, an associate professor of psychiatry and behavioural neuroscience at the University of Chicago who was co-author of the study linking intermittent explosive disorder and toxoplasmosis. He said the study didn’t come close to determining that toxoplasmosis causes the disorder.
“We know that having pets is very good for mental health. It seems to reduce stress and help with social problems,” Lee said.
“So I wouldn’t advise people to do anything different. Because you probably would lose more than you would gain.”