Performance of a Western blot assay to compare mother and newborn anti-Toxoplasma antibodies for the early neonatal diagnosis of congenital toxoplasmosis.

The aim of this study was to retrospectively evaluate the performance of a Western blot assay to compare mother and newborn anti-Toxoplasma gondii antibodies for the early neonatal diagnosis of congenital toxoplasmosis. Since specific anti-Toxoplasma IgM or IgA is detected inconstantly at birth in the neonate, the diagnosis of congenital toxoplasmosis is often delayed until 6-9 months, after IgG titers have been observed persistently. In this study, 81 paired samples from 60 mother/child pairs were tested for IgG and IgM patterns. All mothers had (or were strongly suspected to have) acquired toxoplasmosis during pregnancy. Specific IgM and IgA were simultaneously detected by immunocapture tests, and IgG was titrated. A serological and clinical follow-up of infants was conducted during the first year of life until the diagnosis of congenital toxoplasmosis could be either confirmed or ruled out. Seventeen of the 60 newborns were congenitally infected. Specific IgM or IgA was detected by immunocapture at birth in 76.5% and 70.6% of cord sera from infected neonates, respectively, with an equal specificity of 77.5%. Comparative Western blot allowed the detection of neosynthesized IgG and IgM in the cord blood of 50% and 78.6% of infected infants, respectively, with a specificity of 100%. The combination of IgA and IgM immunocapture tests, the analysis of IgG and IgM Western blot patterns, and the combination of both techniques allowed the detection of 94%, 94%, and 100% of cases within the first 3 months of life, respectively. In conclusion, Western blotting seems to be a useful complementary tool for the early postnatal diagnosis of congenital toxoplasmosis.