Subject:
Suicide

Short Description:
Parasite Infection Possible Precursor to Suicidal Behavior

Background:

A major thrust of much psychiatric research is to identify predictors of suicidality, in hopes of intervening earlier to prevent this devastating outcome. In a recent study, a Danish group made a surprising contribution to this endeavor by identifying Toxoplasma gondii infection as a possible precursor to suicidal behavior.

Toxoplasma is a parasite commonly found in the GI tract of cats, and is carried by almost one-third of adult humans. Humans become infected by exposure to cat feces, eating undercooked meat, and eating unwashed vegetables. Some have linked acute infection to psychotic symptoms, and Toxoplasma antibodies have been found to be elevated in patients with schizophrenia.

Between 1992 and 1995, more than 45,000 pregnant women living in five counties in Denmark, and their newborns, were screened for Toxoplasma IgG antibodies. Nearly 27% of the women were seropositive for IgG, reflecting past infection. Among these women, there were a total of 488 incidents of self-directed violence in the next 10 years of follow-up. These were more common in seropositive women, with a relative risk (RR) of 1.53. The risk was elevated with higher IgG levels, up to a relative risk of 1.91 in those with the highest concentration of antibodies. Also, the risk was greater in women with no past history of mental illness (RR=1.56).

More than 500 women had a prior history of self-directed violence, and 84 had recurrent acts during the study period. Here, too, seropositive women were at higher risk (RR=1.54), although this was not significant. Finally, there were 18 completed suicides in the entire study population, and seropositive women were also overrepresented in this group (n=8), with a relative risk of 2.05. Even though this risk was not significantly elevated, the very low numbers of completed suicides make it hard to draw conclusions about this group.

TCPR's Take:
These results offer an interesting—if unexpected—insight into the neurobiology of self-directed violence. While it’s still a stretch to conclude that Toxoplasma infection causes suicidality, the authors argue that elevations in inflammatory compounds such as interleukin-6 or tumor necrosis factor-a, or in downstream mediators like kynurenines (from the breakdown of tryptophan in the Toxoplasmaparasite) might influence behavior. The study’s findings are limited by the low incidence of actual suicide or self-harm, the inability to assess acuity of Toxoplasma infection, and the exclusion of men. Nevertheless, these findings open the way for further research into biological correlates or biomarkers of violence and suicidality.