Congenital Toxoplasmosis: Value of Antenatal Screening and Current Prenatal Treatment

Introduction Mrs M., a 30 year-old lecturer in psychology is expecting her second baby. Her first baby was born while she was on sabbatical in France. During that pregnancy she was screened for Toxoplasmosis, found to be non-immune and had repeated monthly screening throughout her pregnancy. The consensus in France is to screen all pregnant women for toxoplasmosis at the first visit, and to offer repeated screening to those women who are found to be non immune because of the generally accepted idea that early maternal treatment leads to improved foetal and infant outcome in terms of mortality and severe sequelae in later life. She is concerned that she was not offered screening again during her second pregnancy. She wants to know why screening is not routine in Ireland and if there is any real benefit to be gained from it. Due to her anxieties about Toxoplasmosis she is screened and found to be non-immune at 8 weeks, but at 16 weeks has a Toxoplasma IgM of 1 in 512. She now needs to know what the implications of this result are, and what should be done. To answer Mrs M.’s questions, we will review in this article the consequences of acquiring toxoplasmosis in pregnancy, the criteria to be fulfilled by a good screening programme and the possible benefits and problems related to screening for toxoplasmosis in Ireland. To determine the best approach to the treatment of Mrs M., information about the current management of toxoplasmic infection in pregnancy was sought from a consultant in the Rotunda Hospital. Although the incidence of toxoplasmosis is thought to have increased over the last few years, it is still quite rare in Ireland and no precise protocol exists concerning the approach to adopt. RCOG guidelines were not available from their web site and the opinion of a French obstetrician was sought regarding the topic. The current recommendation in France is to start all mothers suspected of being infected during, or shortly before, the pregnancy on spiramycin to decrease the transmission to the foetus. Prenatal diagnosis is then carried out by PCR on an amniotic fluid sample and infected foetuses are treated in utero by administration of a combination of pyrimethamine and excrete oocytes in their faeces. In humans infection occurs via ingestion of contaminated undercooked food (especially meat) or transplacentally during acute infection in pregnancy, leading to congenital toxoplasmosis. In the immunocompetent host, Toxoplasma infection is usually asymptomatic but can produce a mild self-limiting illness with lymphadenopathy similar to infectious mononucleosis. Congenital infection, however, is a very serious condition with a lethal prognosis in about 10% of cases and a high proportion of disabling sequelae. Toxoplasmosis is a lifelong condition but the foetus is only at risk of congenital disease when acute infection occurs in pregnancy. Placental contamination is a prerequisite to congenital infection and occurs almost only following primary infection when there is maternal parasitaemia. The infected placenta then acts as a reservoir from which the parasite can spread to the fœtus, leading to a multisystemic disease. When the mother is chronically infected by T.gondii, the parasite is dormant in the maternal tissues and there is no parasitaemic phase. Only rarely has congenital infection been reported from a chronically infected immunocompromised mother with a reactivation of toxoplasmosis. Foetal transmission can occur l Review l Obstetrics& Gynaecology