TOXODIAG: New Diagnostic Approach for Congenital Toxoplasmosis

Toxoplasmosis is a cosmopolitan parasitosis that affects one third of the world's population. This infection, caused by Toxoplasma gondii, is mostly asymptomatic except in immunocompromised individuals and infants infected in utero. Congenital toxoplasmosis (CT) results from the transplacental passage of the parasite, which occurs in 30% of cases of primary infection during pregnancy. The clinical consequences are all the more serious when fetal contamination is early (death in utero, premature delivery or term childbirth with perivisceral involvement) and result in mainly neuro-ocular attacks in case of later contamination. Pregnant women or women of childbearing age therefore constitute a group at risk and are exposed differently according to their geographical situation and food consumption. Neonatal biological diagnosis of toxoplasmosis is essential in the case of (i) suggestive clinical signs in the newborn with no information on the serological status of the mother, (ii) seroconversion diagnosed during pregnancy, (iii) not or poorly followed pregnancy, and (iiii) for enhanced effectiveness of treatments administered as soon as possible to the newborn. This diagnosis is based mainly on parasite research in the neonatal amniotic fluid or placenta by PCR and / or inoculation in mice, as well as on serological tests. Immunoglobulins (Ig) A and IgM do not cross the placental barrier and represent good markers of congenital infection in the newborn. Nevertheless, they are not specific to an acute infection and are no longer detectable at birth in cases of infections contracted by the mother before the 3rd trimester of pregnancy. The detection of IgG synthesized by the child has a diagnostic value only after 6 months of life, once the materno-transmitted IgG have been eliminated, and the techniques comparing the IgG response profiles of the mother and the child to a plurality of toxoplasmic antigens remain difficult to interpret (western blot, ELIFA). It is nevertheless a combination of these different tests that makes up the decision tree for a neonatal biological diagnosis of CT. The characterization of specific IgG neo-synthesized by the newborn would be of great help for an early diagnosis of congenital infection by T. gondii. The present project consists in determining the presence in the neonate of B lymphocytes (LyB) sensitized in utero to produce specific IgG in case of CT. This approach can be envisaged because of the maturity acquired by the fetal LyB from the end of the first trimester of pregnancy, demonstrated by their ability to produce high affinity Ig in the case of maternal infection or neonatal immunization.

This research is diagnostic, multicentric, prospective, non-randomized, comparative and controlled. It will be performed in 3 parallel groups of pregnant women performing prenatal follow-up and giving birth in the maternity wards of 3 hospitals of the AP-HP which ensure mother/child follow-up and biological sampling, with great gynecology and obstetrics expertise. Sixty patients will be selected and included according to the following distribution:

• Positive control group (women with positive toxoplasma serology): 15 patients;
• Negative control group (women with negative toxoplasma serology): 15 patients;
• Group of women diagnosed with toxoplasmic seroconversion during pregnancy: 30 patients.

Non-recruiting centers will be HUPC and HUPNVS biology laboratories for the realization of serological tests and expertise in biological diagnosis and IRD UMR 216 for coordination, laboratory experiments and expertise in immunology.