Congenital toxoplasmosis is caused by transplacental fetal contamination following maternal primary infection.
Risk of transmission increases with gestational age. Severity is higher when transmission occurs before 20 WG leading to abortion, fetal loss, prematurity or severe fetal damage (particulary neurological). After this period, infection mainly affects the eye.
Since establishment of prenatal screening in Austria and France, toxoplasmosis has declined. Early maternal treatment (spiramycin or pyrimethamine-sulfonamide) has shown a lower incidence of fetal sequelae. Combination of ultrasound follow-up, fetal MRI, real time PCR on amniotic fluid allows antenatal diagnosis of severe forms of CT in which termination of pregnancy are accepted. Only 15% of infected liveborn children have clinical signs.
In countries with high incidence of CT and without national program, prenatal and/or neonatal screening are required to improve medical care and minimize sequelae (chorioretinitis, hydrocephalus ...). Low prevalence countries recommand neonatal screening or prevention rules.
In case of prenatal diagnosis, clinical examination, serological tests (detection of specific IgM/IgA confirmed at day 10, comparaison of immunologic mother- child profiles), transfontanellar ultrasonography and ocular fundus are performed at birth. In lack of prenatal screening, when children are symptomatic, maternal serology (with avidity test), PCR on placenta, neonatal lumbar punction and tomography are added. In asymptomatic children, diagnosis will be evocated when complications appear (visual impairment, psychomotor delay, seizures...).
Serological tests should be interpreted cautionnely in early or late maternal infection, maternal treatment without amniocentesis. Thus infected children have to be treated early to reduce risk of chorioretinitis.