July 2, 2012 -- Women infected with a parasite found in dirty kitty litter, undercooked meat, and unwashed vegetables may be at higher risk for self-injury and suicide, a new study shows.
In the study, published today in the journal Archives of General Psychiatry, researchers report that women infected with the parasite Toxoplasma gondii were more likely to attempt suicide than women who were not infected.
In the U.S., T. gondii infection is most commonly caused by eating undercooked meat. Infection can also be transmitted from handling infected cat feces, eating unwashed produce, and handling contaminated soil.
The study follows earlier work by the researchers suggesting that T. gondii infection increases the risk for schizophrenia.
Cat Parasite and Suicide
Their latest study, in which nearly 46,000 Danish women who'd had children were followed for more than a decade, found a higher risk of suicide attempts among women infected with T. gondii.
Only 78 women had a violent suicide attempt, which researchers say makes infected women 81% more likely to have a violent suicide attempt than non-infected women; and they were 53% more likely to receive treatment for self-directed violence. Still, the actual risk is very small.
Study co-author Teodor T. Postolache, MD, makes it clear that the study does not prove that T. gondii infection is directly linked to suicide or suicidal actions.
He adds that larger studies will be needed to further explore a possible link.
Postolache is an associate professor of psychiatry and director of the Mood and Anxiety Program at the University of Maryland School of Medicine in Baltimore.
"There is a good possibility that there is some causal link here, but we can't say that with certainty from the research so far," he tells WebMD.
T. gondii Infection Common
About one-third of the world's population is infected with T. gondii, but in most cases people never know it because the infection typically does not cause serious illness.
Newly infected pregnant women can transmit the parasite to their fetuses, which can lead to brain damage, blindness, or severe mental retardation. And people with compromised immune systems are also at risk.
That is why pregnant women and people with weakened immune systems are often advised not to change cat litter boxes.
In the newly reported study, the women were followed for up to 14 years after their T. gondii infection status was determined.
Just 18 women actually committed suicide during the follow-up, which was too small a number to assess the possible impact of T. gondii infection on death from suicide.
And having a personal or family history of mental illness did not appear to significantly alter the findings.
More Study Needed, Researchers Say
The women included in the analysis were enrolled in a larger study examining newborn screening for T. gondii. Because the study did not include men or women without children, it is not clear if the findings can be extrapolated to these groups.
In a prepared statement, J. John Mann, MD, of Columbia University Medical Center, noted that there is mounting evidence that immune factors, such as infection with T. gondii, can impact certain aspects of behavior.
Mann is among the nation's leading suicide researchers.
He added that a better understanding of how latent infections like T. gondii may trigger self-harm responses in people who are already depressed could lead to "new ways of thinking of risk, prevention, and risk reduction for suicide."