A common parasite that can lurk in the cat litter box may cause undetected brain changes in women that make them more prone to suicide, according to an international study.
Scientists have long known that pregnant women infected with the toxoplasma gondii parasite -- spread through cat feces, undercooked meat or unwashed vegetables -- could risk still birth or brain damage if transmitted to an unborn infant.
But a new study of more than 45,000 women in Denmark shows changes in their own brains after being infected by the common parasite.
The study, authored by University of Maryland School of Medicine psychiatrist and suicide neuroimmunology expert Dr. Teodor T. Postolache, was published online today in the Archives of General Psychiatry.
The study found that women infected with T. gondii were one and a half times more likely to attempt suicide than those who were not infected. As the level of antibodies in the blood rose, so did the suicide risk. The relative risk was even higher for violent suicide attempts.
"We can't say with certainty that T. gondii caused the women to try to kill themselves, but we did find a predictive association between the infection and suicide attempts later in life that warrants additional studies," said Postolache, who is director of the university's Mood and Anxiety Program and is a senior consultant on suicide prevention.
"There is still a lot we don't know," he told ABCNews.com. "We need a larger cohort and need a better understanding of the vulnerabilities that certain people have to the parasite."
Suicide is a global public health problem. An estimated 10 million attempt suicide and 1 million are successful, according to Postlache's work.
More than 60 million men, women, and children in the United States carry the toxoplasma parasite, according to the Centers for Disease Control and Prevention, but very few have symptoms.
Toxoplasmosis is considered one of the "neglected parasitic infections," a group of five parasitic diseases that have been targeted by CDC for public health action.
About one-third of the world is exposed to T. gondii, and most never experience symptoms and therefore don't know they have been infected. When humans ingest the parasite, the organism spreads from the intestine to the muscles and the brain.
Previous research on rodents shows that the parasite can reside in multiple brain structures, including the amygdala and the prefrontal cortex, which are responsible for emotional and behavioral regulation.