Common parasite may trigger suicide

MICHIGAN STATE (US) — People who test positive for a common parasite—previously thought to be harmless—are seven times more likely to attempt suicide, a new study shows.

About 10-20 percent of people in the United States have the parasite, Toxoplasma gondii or T. gondii, in their bodies, but in most it is thought to lie dormant, says Lena Brundin, associate professor of experimental psychiatry at Michigan State University.

A new study published in the August issue of the Journal of Clinical Psychology  shows instead that it can cause inflammation over time, which produces harmful metabolites that can damage brain cells.


“Previous research has found signs of inflammation in the brains of suicide victims and people battling depression, and there also are previous reports linking Toxoplasma gondii to suicide attempts,” Brundin says. “In our study we found that if you are positive for the parasite, you are seven times more likely to attempt suicide.”

The new research is the first to measure scores on a suicide assessment scale from people infected with the parasite, some of whom had attempted suicide.

People infected with T. gondii scored significantly higher on the scale, indicative of a more severe disease and greater risk for future suicide attempts, but Brundin stresses the majority of those infected with the parasite will not attempt suicide. “Some individuals may for some reason be more susceptible to develop symptoms,” she says.

“Suicide is major health problem,” says Brundin, noting the 36,909 deaths in 2009 in America, or one every 14 minutes. “It is estimated 90 percent of people who attempt suicide have a diagnosed psychiatric disorder. If we could identify those people infected with this parasite, it could help us predict who is at a higher risk.”

T. gondii is a parasite found in cells that reproduces in its primary host, any member of the cat family. It is transmitted to humans primarily through ingesting water and food contaminated with the eggs of the parasite, or, since the parasite can be present in other mammals as well, through consuming undercooked raw meat or food.

Brundin has been looking at the link between depression and inflammation in the brain for a decade, beginning with work she did on Parkinson’s disease. Typically, a class of antidepressants called selective serotonin re-uptake inhibitors, or SSRIs, have been the preferred treatment for depression. SSRIs are believed to increase the level of a neurotransmitter called serotonin but are effective in only about half of depressed patients.

The research indicates a reduction in the brain’s serotonin might be a symptom rather than the root cause of depression. Inflammation, possibly from an infection or a parasite, likely causes changes in the brain’s chemistry, leading to depression and, in some cases, thoughts of suicide, she said.

“I think it’s very positive that we are finding biological changes in suicidal patients,” Brundin says. “It means we can develop new treatments to prevent suicides, and patients can feel hope that maybe we can help them. It’s a great opportunity to develop new treatments tailored at specific biological mechanisms.”

Teodor Postolache of the University of Maryland was a co-senior investigator of the study, which was funded in part by the Swedish Research Council and the American Foundation for Suicide Prevention.

Source: Michigan State University