Intérêt et limite de la détermination de l'avidité des immunoglobulines G dans le diagnostic de toxoplasmose maternelle

Abstract

The IgG avidity is measured by a modified ELISA test (kit Platelia® Toxo IgG, Sanofi Diagnostics Pasteur) by comparing for each serum at limit dilution, the optical densities obtained with and without washing by a solution of 6M urea. The discriminatory value of IgG avidity to distinguish the acute from the chronic toxoplasmosis is confirmed by the study of three control groups: 14 sera from patients with chronic toxoplasmosis, 21 sera from IgM seropositive patients who show a seroconversion at least seven months old, 11 sera from patients with acute toxoplasmosis. The usefulness of the IgG avidity to date a toxoplasmic seroconversion of the pregnant women is confirmed by the study of 39 sera of 21 patients who raise the problem of the datation of the infection compared to the age of the pregnancy. An avidity index > 0,5 allowed to exclude a toxoplasmosis developing for less than five months. Conversely, an avidity index < 0,5 is not always correlated with a toxoplasmosis developing for less than five months.