Researchers found women infected with the Toxoplasma gondii (T. gondii) parasite, which is spread through contact with cat faeces or eating undercooked meat or unwashed vegetables, are at increased risk of attempting suicide.
The study involved more than 45,000 women in Denmark. About a third of the world’s population is infected with the parasite, which hides in cells in the brain and muscles, often without producing symptoms.
The study’s senior author Doctor Teodor Postolache, an associate professor of psychiatry at the University of Maryland School of Medicine in the United States, said: “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.
“We plan to continue our research into this possible connection.”
Doctor Albert Reece, vice president of medical affairs at the University of Maryland, said: “T. gondii infection is a major public health problem around the world, and many people don’t realize they’re infected.
“Dr Postolache is a leading expert on suicide neuroimmunology. Suicide is a critically important mental health issue. About one million people commit suicide and another 10 million attempt suicide worldwide each year. We hope that this type of research will one day help us find ways to save many lives that now end prematurely in suicide.”
The study is the largest ever of T. gondii and attempted suicide and the first prospective study to document suicide attempts that occurred after the infection was discovered.
Dr. Postolache’s research team at the University of Maryland was the first to report a connection between T. gondii and suicidal behavior in 2009. He is collaborating with researchers in Denmark, Germany and Sweden to confirm and investigate the mechanism leading to this association.
The T. gondii parasite thrives in the intestines of cats, and it is spread through oocysts passed in their faeces. All warm-blooded animals can become infected through ingestion of these oocysts. The organism spreads to their brain and muscles, hiding from the immune system within “cysts” inside cells.
Humans can become infected by changing their infected cats’ litter boxes, eating unwashed vegetables, drinking water from a contaminated source, or more commonly, by eating undercooked or raw meat that is infested with cysts.
Not washing kitchen knives after preparing raw meat before handling another food item also can lead to infection. Pregnant women can pass the parasite directly to their unborn babies and are advised not to change cat litter boxes to avoid possible infection.
Babies don’t produce antibodies to T. gondii for three months after they are born, so the antibodies present in their blood represented infection in the mothers. The scientists scoured Danish health registries to determine if any of these women later attempted suicide, including cases of violent suicide attempts which may have involved guns, sharp instruments and jumping from high places.
The study found that women infected with T. gondii were one and a half times more likely to attempt suicide compared to those who were not infected, and the risk seemed to rise with increasing levels of the T. gondii antibodies.
Dr Postolache noted limitations to the study, such as the inability to determine the cause of the suicidal behavior.
He added: “T. gondii infection is likely not a random event and it is conceivable that the results could be alternatively explained by people with psychiatric disturbances having a higher risk of becoming T. gondii infected prior to contact with the health system.”
The findings were published online in the Archives of General Psychiatry.
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