VIDAS TEST OF IgG AVIDITY FOR DETECTION OF ACUTETOXOPLASMOSIS IN THE EARLY PREGNANCY

Abstract

Toxoplasmosis is usually asymptomatic, but can have severe consequences if it
occurs in immunodeficient subject or fetuses. The diagnosis of toxoplasmosis during
pregnancy is often based on maternal serological testing for IgM and IgG anti-
Toxoplasma antibodies. Persistence of IgM for long periods, posses’ problems in
distinguishing acute from chronic infection. The evaluation of specific IgG avidity
enables more accurate dating, since avidity rises progressively during the course of
infection.
Seventy six women in the first 16 weeks of pregnancy were tested for VIDAS IgM,
IgG antibodies and VIDAS toxo-IgG avidity. Low avidity antibodies were
demonstrated in 2 (33.3%) of 6 sera positive with IgM assay and 4 (12.12%) of sera
positive with IgG assay. Low avidity was also detected in 2 (3.27%) of 61 sera
negative with IgM. The low avidity suggesting a recent infection, while high avidity
in 3 (50%) of the 6 positive IgM and 24 (72.72%) of 33 positive IgG indicating that
the infection acquired in the distant past. These findings highlight the value of
VIDAS IgG avidity when used in combination with the VIDAS IgM and IgG assays
to provide a confirmatory evidence of an acute infection with a single serum
specimen for pregnant women.