The parasite Toxoplasma gondii (T. gondii), long thought to be harmless, instead has been found to cause changes in the human brain so harmful that for some, they include attempts at suicide, a research team reports.

In a study published in this month’s issue of The Journal of Clinical Psychiatry, a team of researchers from the U.S., Sweden, and Egypt linked T. gondii to inflammation over time causes changes to the brain—namely the production of harmful metabolites that can damage brain cells.

Researchers discovered a seven-fold increase in nonfatal suicidal self-directed violence in people testing positive for T. gondii IgG antibodies compared with people who tested negative. The result is five times the increase associated with the parasite in previous studies that did not specifically focus on self-directed violence.

Worse, reported the researchers, the correlation with attempted suicide was specific to T. gondii antibodies as opposed to antibodies to other neurotropic organisms, such as CMV or HSV-1.

“In the long term, T. gondii antibodies might become a candidate marker to improve our ability to estimate risk of nonfatal suicidal self-directed violence and to individualize interventions in suicide prevention,” the research team concluded.

The team also suggested avenues for future study that could help save lives: “Future replication of T. gondii-related nonfatal suicidal self-directed violence in prospective studies could potentially have public health impact. Additionally, studying the outcome of fatal self-directed violence in a large cohort, as well as uncovering mechanisms involved in the association, may have future therapeutic and preventive impact.”

For example, researchers added, individuals otherwise deemed at risk of suicide could someday be screened for T. gondii antibodies, while the parasite’s marker could aid in development of a vaccine or other therapies.

T. gondii is found in cells that reproduce in its primary host, any member of the cat family. The parasite 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.

“I think it’s very positive that we are finding biological changes in suicidal patients. It means we can develop new treatments to prevent suicides, and patients can feel hope that maybe we can help them,” Lena Brundin, M.D., Ph.D., of Michigan State University, who co-led the research team with Teodor Postolache, M.D., of the University of Maryland, said in a statement.

[Read the full study here:]

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