Common Cat Parasite May Up Suicidality in Expectant Moms

Deborah Brauser

July 06, 2012

July 6, 2012 — Expectant mothers infected with the parasite Toxoplasma gondii (T gondii) are at risk for later self-directed violence, including suicidality, new research suggests.

A large cohort study showed that mothers infected with T gondii at time of delivery were 53% more likely to self-injure during the 11 to 14–year follow-up period than their counterparts who were not infected.

Adjusted analysis revealed that the risk remained significant even for women without a history of mental illness.

In addition, "the risk of attempting suicide seems to increase with increasing Toxoplasma gondii immunoglobulin G antibody level," Marianne Giørtz Pedersen, from the National Center for Register-Based Research at Aarhus University, Denmark, told Medscape Medical News.

"Based on the findings, it seems advisable to take natural precautions to avoid Toxoplasma gondii infection," added Pedersen.

The primary host for T gondi is cats, but other warm-blooded animals, including mice, birds, and humans, can also host the parasite.

The study was published online July 2 in the Archives of General Psychiatry.

Research Adding Up

In 2011, and as reported at the time by Medscape Medical News, Pedersen and colleagues published a study in the American Journal of Psychiatry showing an association between T gondii infection and development of schizophrenia in women who had recently given birth.

Further, at this year's American Psychiatric Association Annual Meeting, researchers from the University of Maryland School of Medicine presented a study that included 950 patients (63% men) who had schizophrenia. The results showed a link between T gondii infection and suicidality.

For the current analysis, investigators examined data from a cohort of Danish women originally recruited to participate in a study of neonatal screening for T gondii. They assessed records for 45,788 women who had given birth from 1992 to 1995; follow-up was concluded in 2006.

T gondii immunoglobulin G (IgG) levels were measured from blood samples drawn from the offspring 5 to 10 days after birth.

These IgG antibodies "were maternal in origin, because IgG passes through the placenta, and infected newborn children will not begin producing T gondii–specific IgG until approximately 3 months of age," report the researchers.

An IgG level "more than 24" qualified mothers as being seropositive for the infection at time of delivery.

The Danish Cause of Death Register, National Hospital Register, and Psychiatric Central Research Register were all examined for information on participants' possible completed suicides, in- and outpatient hospital stays, and psychiatric diagnoses.

A Clear Link

During follow-up, results showed that 448 of the women had a first episode of self-directed violence (517 others had participated in self-injury prior to delivery), 78 had a violent suicide attempt, and 18 were suicide completers.

A total of 26.8% of all participants were seropositive for T gondii at time of delivery.

Mothers who had a T gondii infection were significantly more likely to later participate in self-directed violence than those without the infection (relative risk [RR], 1.53; 95% confidence interval [CI], 1.27 - 1.85; P < .001).

The RRs for self-directed violence increased significantly for the infected women as the IgG antibody level increased:

T gondii IgG Level RR (95% CI)
25 - 45 1.08 (.70 - 1.58)
46 - 58 1.49 (1.06 - 2.04)
59 - 71 1.55 (1.10 - 2.12)
72 - 83 1.87 (1.30 - 2.61)
≥84 1.91 (1.25 - 2.79)

All RRs, P < .001.

For all women with a history of a psychiatric disorder, those who also had a T gondii infection had an RR of 1.25 compared with those without an infection. The RR was even higher, at 1.56, for women with the infection but without a psychiatric disorder.

However, the researchers note that the fact that the latter finding was higher than the previous one "should be interpreted with caution."

In other results, all women with an infection had an RR of 1.81 for violent suicide attempts and an RR of 2.05 for completed suicides compared with the noninfected women.

"A similar association was found for repetition of self-directed violence, with a relative risk of 1.54," report the investigators.

They note that the results show a clear association between T gondii infection and self-directed violence.

If confirmed in future research, and if the underlying cause can become better understood, the findings "may lead to new prognostic, prophylactic, and therapeutic approaches to suicide prevention," the researchers conclude.

The study was supported in part by the American Foundation for Suicide Prevention; the VA Capitol Health Care Network Mental Illness Research, Education, and Clinical Center; and the Stanley Medical Research Institute. The study authors have disclosed no relevant financial relationships.

Arch Gen Psychiatry. Published online July 2, 2012. Full article

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