More Evidence Links Common Parasite to Suicidal Behavior

Deborah Brauser

August 21, 2012

August 21, 2012 — Individuals infected with the Toxoplasma gondii parasite are at significant risk for later suicide attempts, new research suggests.

A cohort study of 84 adults from Sweden showed that those who had been infected with T gondii were 7 times more likely to participate in nonfatal, self-directed violence compared with their counterparts who had not been infected.

"The most surprising thing was how high the increased risk was," co–senior author Lena Brundin, MD, PhD, associate professor of experimental psychiatry in the Department of Translational Science and Molecular Medicine at Michigan State University College of Human Medicine in Grand Rapids, told Medscape Medical News.

Dr. Lena Brundin

She noted that the results confirm other recent research in finding an association between T gondii and suicidality in various populations.

"It appears that this parasite can cause inflammation over time, which produces harmful metabolites that can damage brain cells," said Dr. Brundin in a release.

However, she stressed that not everyone infected will go on to attempt suicide. "For some reason, some people may be more susceptible to developing symptoms than others."

"Still, it's a great opportunity to develop new treatments tailored at specific biological mechanisms," she said. "The take-home message is that this is a positive finding, that we're finding new potential biological causes for suicidality."

The study is scheduled to be published in the August issue of the Journal of Clinical Psychiatry.

According to the investigators, approximately 10% to 20% of people in the United States currently have T gondii antibodies.

Mounting Evidence

Two months ago, Medscape Medical News reported findings from a study published in the Archives of General Psychiatry that showed that expectant mothers who were infected with T gondii at time of delivery were 53% more likely to self-injure than their uninfected counterparts.

In a study published in 2011 in the American Journal of Psychiatry, the same researchers found a link between T gondii and development of schizophrenia in women who had recently given birth.

At this year's American Psychiatric Association (APA) Annual Meeting, investigators presented results from a study that included 950 individuals, 63% of whom were men, who had schizophrenia. A significant association was found between T gondii infection and suicidality in the participants who were younger than 39 years, but not in those who were older.

For this study, Dr. Brundin and colleagues compared T gondii antibody titers in plasma samples collected in Lund, Sweden, from 54 adults who had previously attempted suicide (57.4% women; mean age, 38.4 years) and from 30 healthy control participants (63.3% women; mean age, 39.8 years).

The most common psychiatric disorders found in those who had attempted suicide included personality disorder not otherwise specified (n = 25), bipolar II disorder (n = 10), and major depressive disorder (n = 7). Exclusion criteria for the healthy control participants included prior suicide attempts or prior psychiatric treatment.

The self-rated Suicide Assessment Scale (SUAS-S) and the Montgomery-Åsberg Depression Rating Scale (MADRS) were administered to all participants.

Participants with an immunoglobulin G level of 22 or more IU/mL were considered to be seropositive for T gondii infection. The plasma samples were also tested for cytomegalovirus and herpes simplex virus type 1.

Important Predictor

Results showed that the adjusted odds ratio (OR) associating seropositivity for T gondii to nonfatal, self-directed violence was 7.12 (95% confidence interval [CI], 1.66 - 30.6; P = .008). The adjusted OR for serointensity was 2.01 (95% CI, 1.09 - 3.71; P = .03).

"Nonfatal suicidal self-directed violence [is] the most important predictor of fatal suicidal self-directed violence," write the investigators.

In addition, all participants who tested positive for T gondii antibodies had a mean SUAS-S score that was 13 units higher than the mean score for participants who had not been infected (P = .026).

However, this relationship was only significant for the entire group and not for the nonfatal suicide attempters only. T gondii serointensity was not significantly associated with the SUAS-S.

There were also no significant associations found between depression symptoms/MADRS scores and either T gondii seropositivity or serointensity, nor were any associations found between self-directed violence and cytomegalovirus or the herpes virus.

"The consistency of T gondii's association with nonfatal suicidal self-directed violence across studies, regardless of the patient sample and...diagnostic category, is noteworthy, as it lends further credence to the hypothesis that the link is independent of mental illness specificity or severity," write the researchers.

Dr. Brundin noted that there are currently no clinical recommendations for treating T gondii infections.

"So at this stage, I think we should look at this as very positive, in that we are finding biological changes in suicidal patients," she said.

"It means we can perhaps develop new treatments to prevent suicides, and patients can feel hope that maybe we can help them."

The study was supported by several grants and organizations. A full list of funding organizations can be found in the original article. The study authors have disclosed no relevant financial relationships.

J Clin Psychiatry. 2012;73:1069-1076. Abstract


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