As with German measles, a woman infected prior to her pregnancy has essentially no chance of giving birth to an infected child. "But if the woman first becomes infected during pregnancy, her fetus is at severe risk of becoming infected," Remington said. "And that infection can cause disastrous results in the newborn -- blindness, epilepsy, psychomotor retardation or mental retardation."
Between 1,000 and 4,000 infants born in the United States each year have congenital toxoplasma infections. Infected newborns often appear healthy at birth, but if the infection is unrecognized and thus untreated, 90 percent later suffer disabilities such as mental retardation, blindness or epilepsy.
"If I could tell pregnant women just one thing," Remington said, "it would be: Eat all your meat well cooked." A woman infected during the first trimester of pregnancy has a 15 percent chance of passing the parasite to her fetus. When the infection occurs later in pregnancy, the risk increases. Women infected during their third trimester have a 60 percent chance of transmitting the parasite to their unborn children. "If you don't screen the mother for the appearance of antibodies, she won't know because the infection is almost always asymptomatic," Remington said. "That is the tragedy."
A pioneer of toxoplasma research, Remington in the early 1970s developed the IgM test, which is the standard test for toxoplasmosis. IgM is the first antibody created when the body is infected or immunized. Initially researchers believed a positive test for IgM meant a recently acquired infection. However, the IgM antibody for toxoplasmosis is uncharacteristic in that it may persist for a year or more -- far beyond the point at which an infected mother could transmit the microbe to her fetus. Remington said some physicians continue to misinterpret the IgM test results, leading to many unwarranted abortions.