A common parasite may significantly increase women’s risk of self-destructive behaviors, including suicide attempts and self harm, according to a study conducted by researchers from the University of Maryland School of Medicine in Baltimore and published in the Archives of General Psychiatry.
The parasite in question is known as Toxoplasma gondii, and infection with it is known as toxoplasmosis. The most common sources of human exposure are undercooked meat, unwashed vegetables and the feces of domestic cats. Although other animals can become infected with the parasite, only cats shed it in their feces.
T. gondii is most common in warm, humid climates, and chronic human infection rates in such regions (including Central and Southern Europe, Asia, Africa and South America) can reach 50 percent. Although toxoplasmosis is usually asymptomatic in adults, it can be dangerous to anyone with a compromised immune system.
In addition, the parasite can pass from a pregnant woman to her fetus, with potentially severe results. Between the 10th and 24th weeks of pregnancy, toxoplasmosis can lead to low birth weight, premature birth, jaundice, abnormal head size, retinal abnormality, convulsions, brain calcification or mental retardation in the infant. After the 24th week, the fetus is well-developed enough that the risks from infection drop significantly.
An estimated one out of 1,000 to 8,000 children born in the United States tests positive for toxoplasmosis.
Effects on the Brain?
The T. gondii parasite lives in the brain, which may explain why it damages the brains of developing fetuses and has also been linked to a higher risk of schizophrenia in adults. In the new study, the researchers sought to determine whether the parasite can have direct effects on human mood and behavior.
The researchers used Danish medical records to track 45,788 women who had taken part in a newborn toxoplasmosis screening study, in which their infants were screened for the parasite within 10 days of birth. More than one in four infants tested positive, thus indicating that their mothers likely suffered from chronic toxoplasmosis.
Over the following 14 years, 78 of the women attempted suicide and 488 engaged in self-harm. The researchers found that the rate of self-harm was 50 percent higher among women with toxoplasmosis, and the rate of attempted suicide was 80 percent higher.
A total of 18 women successfully committed suicide, but this number was too small for comparison. Other potential weaknesses in the analysis included the fact that not all cases of self-harm were necessarily reported to physicians, and that the correlation found between toxoplasmosis and self-destructive behavior might not be causative. For example, it is possible that some third factor, such as underlying depression, produced both the self-destructive behavior and an increased infection risk (such as from a depressed immune system or poor hygienic practices).
Nevertheless, lead researcher Teodor Postolache believes that the study supports the hypothesis that T. gondii has some effect on the brain. For example, the parasite might directly affect the production of mood-regulating neurotransmitters.
“It’s [also] possible that the immune system containing Toxoplasma gondii does it at the cost of affecting brain function,” he said.
Toxoplasmosis researcher Louis Weiss of Albert Einstein College of Medicine in New York, who was not involved in the study, suggested that the parasite might trigger inflammation, which in turn might change the chemical balance in the brain.
The risk of contracting toxoplasmosis from domestic cats is relatively small, and there is no need for pregnant women to get rid of their cats. To be safe, however, pregnant women should avoid changing litter boxes. If they must change a litter box, pregnant women should wear rubber gloves, then thoroughly wash their hands.