Common parasite linked to suicide

July 7, 2012 - 05:00

The risk of committing suicide is higher for women who have toxoplasmosis, concludes a study of Danish women.

Every year around one million people succeed in taking their own lives and ten million attempt to do so. (Photo: Colourbox)

Suicide is one of the common causes of premature deaths around the world. Every year around one million people succeed in taking their own lives and ten million attempt to do so.

Earlier research has indicated that an infection by the Toxoplasma gondii parasite can be linked to such tragic events. This suspicion has now been confirmed by the largest ever study on the subject.

Danish, Swedish, German and American researchers have collaborated on a study of 45,000 Danish mothers who were followed up for up to 14 years.

The results show the incidence of suicide attempts is 50 percent higher among women with toxoplasmosis than for women without the infection.

“We can’t say with certainty that T. gondii made the women try to take their lives, but we found a predictive association between the infection and suicide attempts later in life that justifies further studies,” says Theodor T. Postolache of the University of Maryland.

Cat parasite

The toxoplasmosis parasite has actually specialised in a life linked to felines. It can only reproduce inside the intestines of cats, where it creates spores that are released with cat faeces.

However, any warm-blooded animals that get the spores inside them can become infected. The parasite spreads to muscle tissue and the brain, and hides out inside the host body’s own cells. It can hibernate indefinitely.

But a number of studies indicate the parasite isn’t completely inactive in its hideaway. Research reveals how T. gondii makes rats and mice lose their fear of cats.

A third of the world is infected

Human beings are also easily infected by the parasite from contact with cat dung, raw or poorly cooked meat, or unwashed vegetables. Scientists believe that around a third of the world’s seven billion people are infected.

A foetus can be harmed if a woman contracts toxoplasmosis while she’s pregnant.  This is why pregnant women are often tested for it. The team of researchers has analysed data from 45,788 women who gave birth in the years from 1992 to 1995.

The comprehensive health registries in Denmark have given researchers access to information about suicide attempts, previous mental illness and other relevant factors.

The parasite isn't necessarily to blame

The results show that mothers hosting the common parasite run a greater risk of suicide. The figures also point toward a stronger link with higher levels of antibodies against T. gondii.

In addition, the study indicates that the infection can be tied to an increased risk of more violent suicide attempts, such as the use of firearms, sharp objects or jumps from high places.

Nevertheless, the researchers have no definite answers regarding how the infection links to suicides.

The risk of being infected by T. gondii hinges on behaviour; it’s associated with keeping cats as well as eating habits. So it is feasible that underlying causes can yield a higher risk for toxoplasmosis, according to Postolache.

Are the suicide attempts a direct effect of the parasite on brain function or an exaggerated immunity response induced by the parasite that impacts the brain?

“We don’t know. We actually haven’t ruled out an opposite cause-and-effect relationship, as risk factors for suicidal behaviour could also make people more vulnerable to infections by T. gondii.”

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Translated by
Glenn Ostling