Contribution of the Toxoplasma ICT IgG IgM® test in determining the immune status of pregnant women against toxoplasmosis.

BACKGROUND: An immunochromatography technology (ICT) rapid diagnostic test, the Toxoplasma ICT IgG-IgM® , was recently developed. Our aim was to study its contribution to establish accurately the Toxoplasma immune status in Tunisian pregnant women using Western blot (WB) Toxo II IgG® as a reference technique. METHODS: Thirty-nine sera were selected for the study from among 2,615 which were already tested by IgG and IgM ELISA. They displayed equivocal IgG titres (4.4-9 IU/ml) in absence of IgM (19 sera) or IgM anti-Toxoplasma antibodies in absence of IgG (titre <4.4 IU/ml) (20 sera). All these sera were additionally tested by WB Toxo II IgG® . RESULTS: Immunochromatography technology Sensitivity in the detection either of low IgG titres in absence of IgM or of specific anti-Toxoplasma IgM was 100%. Only one serum with equivocal IgG titre by ELISA and negative with Toxo II IgG® test revealed positive in ICT. However, this serum showed a P30 band in WB analysis. On the other hand, three sera positive in ELISA IgM and negative in ELISA IgG revealed positive in ICT and negative in WB Toxo II IgG® , the reference test. CONCLUSION: Results confirm the high sensitivity of Toxoplasma ICT IgG-IgM® in detecting both specific anti-Toxoplasma IgG and IgM, and highlight the usefulness of this rapid test as a first or second-line Toxoplasma serological test in pregnant women.

A New IgG Immunoblot Kit for Diagnosis of Toxoplasmosis in Pregnant Women

The determination of the accurate immune status of pregnant women is crucial in order to prevent congenital toxoplasmosis. Equivocal results with conventional serological techniques are not uncommon when IgG titers are close to the cut-off value of the test, so that a confirmatory technique is needed. For this purpose, we developed a homemade immunoblot (IB) using soluble extract of Toxoplasma gondii tachyzoites and assessed it by testing 154 positive, 100 negative, and 123 equivocal sera obtained from pregnant women. In order to select the more valuable bands in terms of sensitivity and specificity, we used the Youden Index (YI). The highest YIs were those given by the 32, 36, 98, 21, and 33 bands. The simultaneous presence on the same blot of at least 3 bands showed a much higher YI (0.964) and was adapted as the positivity criterion. The analysis of results showed that our homemade IB correlated well with the commercial LDBIO Toxo II IgG(R) kit recently recommended as a confirmatory test (96.7% of concordance).

[Difficulty in dating primary infections by Toxoplasma gondii in pregnant women in Tunisia]. / Difficultés de la datation de la primo-infection par Toxoplasma gondii chez les parturientes en Tunisie.

In Tunisia, serological diagnosis of toxoplasmosis in pregnant women is generally ordered on the first prenatal consultation. As primary tools, IgG and IgM tests are done. Subsequent serological testing is performed to date infection in case of IgM positivity. IgG avidity measurement was done in 156 sera with IgM. The kit "Toxo Avidité" from SFRI was used. This commercial assay permits to rule out an infection acquired in the last 12 months in case of avidity index (AI) > 0.6 and to suspect a recent infection acquired in the last 3 months in case of AI < 0.3, 57.1% of pregnant women had an Al > 0.6: 17.9% an Al < 0.3 and 25% an intermediate Al. The high and middle IgG titles were frequently associated with an AI > 0.6 whereas low titles were generally associated with an AI < 0.6 (p < 0.01) and particularly an IA < 0.3. If an Al > 0.6 is an indicator against primary infection during pregnancy and an AI < 0.3 permits to order amniotic sampling for PCR, intermediate avidity dols not permit to conclude mainly because a great proportion of pregnant women do not lave their first prenatal consultation befoe the second trimester of pregnancy. In these cases search for IgA and follow-up samples can be useful. To facilitate serological interpretation, the antibody status of pregnant women should be obtained in Tunisia, before or early in pregnancy.