3 July 2012

Toxoplasmosis linked to suicide attempts

by Will Parker

Spread through contact with cat feces or eating undercooked meat, the parasite Toxoplasma gondii (T. gondii) has been linked to increased rates of attempted suicide in women. The study, in the Archives of General Psychiatry, notes that while causality has not been proven, a significant predictive association exists between the infection and suicide attempts later in life.

Around one-third of the world's population is infected with the parasite, which hides in cells in the brain and muscles, often without producing symptoms. Toxoplasmosis infection has been linked to mental illness, such as schizophrenia, and changes in behaviour.

The parasite thrives in the intestines of cats, is spread via their feces and can infect all warm-blooded animals. 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.

In the new study, researchers analyzed data from more than 45,000 women in Denmark who gave birth between 1992 - 1995 and whose babies were screened for T. gondii antibodies. 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 then scoured Danish health registries to determine if any of these women later attempted suicide. They also cross-checked records in the Danish Psychiatric Central Register to determine if the women had been diagnosed previously with mental illness.

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. Interestingly, the risk rose with increasing levels of the T. gondii antibodies and previous mental illness did not significantly alter these findings.

Study leader Teodor T. Postolache, associate professor of psychiatry and director of the Mood and Anxiety Program at the University of Maryland School of Medicine, said that one of the strengths of the study was that researchers were able to adjust for various factors, such as prior history of mental illness, not only in the subjects, but also in their parents.

But, he also notes limitations to the study, such as the inability to determine the cause of the suicidal behavior. "Is the suicide attempt a direct effect of the parasite on the function of the brain or an exaggerated immune response induced by the parasite affecting the brain? We do not know. In fact, we have not excluded reverse causality as there might be risk factors for suicidal behavior that also make people more susceptible to infection with T. gondii," Postolache explained. "If we can identify a causal relationship, we may be able to predict those at increased risk for attempting suicide and find ways to intervene and offer treatment."

Commenting on the study, Columbia University's J. John Mann, an expert on suicide, says that evidence is accumulating on immune factors being associated with suicidal behavior. "Identifying neurotropic latent infections potentially triggering or perpetuating a heightened immune response in patients at risk could lead to new ways of thinking of risk, prevention and risk reduction for suicide."

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Source: University of Maryland Medical Center