Could eating rare steak give you road rage?

Could eating rare-cooked meat give you road rage? That is the intriguing question posed by new research into the parasitic bug toxoplasma gondii which will, at some point, infect half of adults.

The bug causes toxoplasmosis in the brain and we contract it primarily from handling or eating raw and undercooked red meat, such as lamb, or through contact with cats.

In most cases, the parasite is infective for only a few weeks after you have contracted it, though the very mild flu-like symptoms of initial infection are usually so subtle that most people never notice they have had it; then the bug goes into a long-term dormant or ‘latent’ stage.

This dormant stage was considered generally harmless, but that view is now changing, thanks to mounting evidence that it can influence people’s behaviour by altering the chemistry of their brains, making some people more aggressive, reckless, impulsive and more likely to put themselves in danger.

last month, scientists at the university of Chicago reported that people who explode into bouts of extreme anger such as road rage are twice as likely to have dormant toxoplasmosis.

‘our work suggests latent infection with the toxoplasma gondii parasite may change brain chemistry in a fashion that increases the risk of aggressive behaviour,’ says Emil Coccaro, a professor of psychiatry and behavioural neuroscience, who led the study of 358 adults. He stresses that he has not established cause and effect, which is difficult to do when linking highly complex brain chemistry with behaviour.

However, uncontrollable rage is only the latest in a series of perilous psychological effects to be linked with toxoplasmosis. Numerous studies have shown an association with depression and suicide.

In 2012, a Maryland university study of more than 80 people in the Swedish city of lund found that those whose blood tested positive for exposure to toxoplasmosis were seven times more likely to have attempted suicide.

Potential links between the parasite and mental illness emerged nearly 60 years ago. In 1959, a report in The lancet by psychiatrists at St luke’s Hospital in Middlesbrough linked a 32-year- old woman’s schizophrenia with her contracting toxoplasmosis. Since then, numerous studies have found unusually high levels of toxoplasmosis among patients with schizophrenia.

last July, a study in the Journal of Affective disorders, led by the French National Institute for Health and Medical Research, suggested toxoplasmosis causes brain inflammation, which may underlie the condition.

PROFESSOR Joanne Webster, chairwoman of parasitic diseases at the university of london, is an expert in toxoplasmosis and is investigating how the parasite may cause schizophrenia.

She believes that latent toxoplasmosis can boost levels of the ‘ reward’ chemical dopamine in the brain. This chronic overstimulation is believed to cause some people to suffer such psychotic symptoms as confusion, delusions and hallucinations.

‘ It is not only altering the host’s dopamine levels, the parasite is also producing its own dopamine,’ she says. ‘There are, however, almost certainly multiple other mechanisms it is using to alter the host’s behaviour, but we are yet to discover them.

‘It is likely that, with more research, people will find toxoplasmosis is involved with more psychiatric conditions.’

once ingested, the parasite travels to the brain through the bloodstream and ‘hides’ from our immune defences.

‘It has been assumed to spend many years being asymptomatic and dormant, but I think the effects are still going on a lot more than people think, affecting the mind and perception of the host,’ says Professor Webster.

These effects may include reaction times, as the infection has been linked to an increased risk of having a traffic accident. A study of nearly 4,000 military drivers in 2009 found that those with latent infections are up to six times more likely to have been involved in a crash.

Jaroslav Flegr, a professor of biology at Charles university in Prague, who led the research, believes the risk of accidents is raised because toxoplasma can slow people’s reaction times and make them more likely to act impulsively.

But why would a parasite want to make us behave in a dangerous way? Professor Flegr and other researchers argue toxoplasma parasites change their hosts’ behaviour in ways that benefit the parasite, not us.

He says our brains provide a handy staging point where the parasite can live until it can infect an animal in which it can reproduce, because while toxoplasmosis can live in any warm-blooded animal, it can only sexually reproduce inside cats, be they big ones or domestic pets. The theory is that putting ourselves in harm’s way is more likely to kill us and give the bug a chance to escape and pass to its ideal host.

Intriguingly, as well as making us reckless and slowing our reaction times, it also makes us more drawn to cats — which in our ancestors’ day would have increased the chances of being eaten by a big cat.

STUDIES by Professor Flegr have found that students whose blood tested positive for the parasite were attracted to the smell of cat urine. Professor Webster has studied this phenomenon in rats.

‘The infection overrides rats’ strong, innate fear of domestic cats, in what we called a “fatal feline attraction”,’ she says. ‘Infected rats particularly love the smell of puma and cheetah urine.’

There are no drugs available specifically to treat people’s brains for the latent effects of toxoplasmosis. Professor Webster believes we need to develop some, as this may help to resolve some of the symptoms of infected people with conditions such as schizophrenia.

Nevertheless, she says, many behavioural changes caused by the parasite remain, even if all evidence of it has been cleared from the host’s brain.

Pet cats get most of the blame for spreading the parasite (it’s in their faeces), but Professor Webster points to another culprit: ‘Most of us don’t get toxoplasmosis from cats, but from undercooked meats.’

Pregnant women should avoid cat litter and wash their hands thoroughly after handling cats, as toxoplasmosis can cause miscarriage or birth defects.

The Food Standards Agency recommends that meat should be cooked ‘until no trace of pinkness remains and the juices run clear’. It says we should not taste meat before it is fully cooked and should wash our hands after handling raw meat.

As a vegetarian — an allotment-owning one, too — I smile smugly until she warns: ‘If cats are on the allotment and you don’t scrub your veg, you can get infected from their stools . . .’