Pregnant women with high levels of antibodies to a common parasite, Toxoplasma gondii, run the risk having a child who will develop schizophrenia or a schizophrenia-like disorder in adulthood, US researchers suggest.

Infection with Toxoplasma is widespread. People can pick it up quite easily, especially when cats are around because the animals frequently harbor the parasite.

A pregnant woman who contracts toxoplasmosis can pass the parasite on to her unborn baby, with serious consequences.

On the other hand, a woman who has had the infection and has become immune cannot pass the organism on to her baby during pregnancy.

If the infection is spotted, pregnant women can be treated with antiparasitic drugs to lower the risk to their babies.

“Given that toxoplasmosis is a preventable infection,” say the authors of the new study, “the findings, if replicated, may have implications for reducing the incidence of schizophrenia.”

As reported in the American Journal of Psychiatry, Dr. Alan S. Brown, from the New York State Psychiatric Institute in New York, and colleagues, evaluated the link between maternal exposure to Toxoplasma and schizophrenia risk in a large group of people born between 1959 and 1967.

They identified 63 people who developed schizophrenia and compared them with 123 similar “controls” without schizophrenia. The researchers tested stored blood samples, obtained from the mothers while they were pregnant, for Toxoplasma antibodies. Antibody levels were classified as negative, moderate, or high.

A high Toxoplasma antibody level, indicating heavy infection around the time of pregnancy, more than doubled the likelihood of schizophrenia in the adult offspring. By contrast, moderate levels seemed to have no effect on the risk.

“The findings may be explained by reactivated infection or an effect of the antibody on the developing fetus,” the researchers conclude.

“These findings add to a growing literature suggesting a relationship between in utero exposure to infectious agents that are known to disrupt fetal brain development and the risk of adult schizophrenia,” they add.

SOURCE: American Journal of Psychiatry, April 2005.