Intravenous immunoglobulin therapy: confounding effects on serological screening for toxoplasmosis during pregnancy.

The serological diagnosis of toxoplasmic infection during pregnancy is intended to prevent congenital infection of the fetus. However, in the context of recurrent pregnancy loss intravenous immunoglobulin therapy can create a biological trap for the interpretation of serological results, with potentially serious consequences for the outcome of the pregnancy.

Lack of value of specific IgA detection in the postnatal diagnosis of congenital toxoplasmosis.

To improve the performance of the postnatal diagnosis of congenital toxoplasmosis, we assessed the detection of IgA antibodies to Toxoplasma gondii by ELISA, compared with that of IgM by ELISA, ISAGA, and IFAT and neosynthesized antibodies using Western blot. From 1993 to 1996, IgA antibodies were detected using the Toxo IgA test (SFRI, Société Française de Recherches et d'Investissements, Bordeaux, France), in 195 serum and cord blood samples from 63 infants born to mothers who seroconverted during pregnancy. Eighteen infants had proven congenital toxoplasmosis (confirmed by the presence of IgG after 12 months of life) and 45 had no congenital toxoplasmosis (negativity of IgG after 6-12 months of life). The sensitivity of IgA detection by ELISA on serum and cord blood samples was 38.9 and 54.5% respectively, which is low when compared with the sensitivity of IgM detection by ISAGA (66.7% on serum samples, 90.9% on cord blood), ELISA (61.1% on sera, 81.8% on cord blood) and Western blot (83.3% on sera, 72.7% on cord blood). IgA antibodies were never detected by ELISA earlier than IgM or neosynthesized Ig (antibodies synthesized by infants). Thus, the detection of IgA antibodies by Toxo IgA is not useful in improving the diagnosis of congenital toxoplasmosis.

Determination of anti-Toxoplasma gondii immunoglobulin G avidity: adaptation to the Vidas system (bioMérieux).

The determination of specific anti-Toxoplasma gondii IgG avidity has been proposed to improve the determination of the date of toxoplasmic seroconversion in pregnant women. In this study, we adapted this serological technique to the Vidas system (bioMérieux) using 6 M urea as the dissociating agent. We studied 356 sera, including 42 sequential sera from sero-conversions in pregnant women. Our results show that the test is easy to use, and that an avidity index higher than 0.300 allows the exclusion of a recent infection acquired less than 4 months before serum sampling.

Detection of Toxoplasma gondii in 94 placentae from infected women by polymerase chain reaction, in vivo, and in vitro cultures.

The biological diagnosis of congenital toxoplasmosis at birth is important to determine the infant's treatment. The aim of this study was to evaluate the placenta results in the congenital toxoplasmosis diagnosis and to compare them with those obtained with other samples collected at birth (cord blood and newborn blood). A total of 94 placentas, of which 33 came from fetuses suspected of or with proven congenital toxoplasmosis (CT+) and 61 from definitely or probably non-infected fetuses (CT-), was analysed by in vitro culture, mouse inoculation and polymerase chain reaction (PCR). The PCR sensitivity was higher (60.9 per cent) than that of cell culture (29.6 per cent) and mouse inoculation (51.5 per cent) but the number of PCR positive results in CT - patients was also higher (9.5 per cent). The presence of Toxoplasma gondii in the placenta tissues was the only argument at birth (IgM and neosynthesized Ig were negative) in three out of the 33 CT+ cases. The detection of IgM by ELISA and ISAGA and the detection of neosynthesized Ig by immunoblotting were more satisfactory to diagnose congenital toxoplasmosis but the placenta analysis was important to improve the sensitivity of the diagnosis at birth, especially when the prenatal diagnosis was negative or not performed.

Prenatal diagnosis of congenital toxoplasmosis: comparative value of fetal blood and amniotic fluid using serological techniques and cultures.

The prenatal diagnosis of congenital toxoplasmosis is mainly based on biological tests performed on fetal blood and amniotic fluid. We studied the performance of neonatal diagnosis procedures and the results of fetal blood and amniotic fluid analysis. Of 127 women who contracted toxoplasmosis and underwent prenatal diagnosis, the postnatal serological follow-up was long enough to definitively diagnose congenital toxoplasmosis in 19 cases and to exclude it in 27 cases. Prenatal diagnosis allowed the detection of 94.7 per cent (18/19) of the infected fetuses. The sensitivities of tests in amniotic fluid and fetal blood were equivalent, 88.2 per cent (15/17) and 87.5 per cent (14/16), respectively. In fetal blood, biological techniques were positive in 12/16 cases and in 2/16 cases, serological tests were the only positive sign. The specificities of tests in amniotic fluid and fetal blood were respectively 100 per cent (23/23) and 86.3 per cent (19/22) (three false-positive serological results). These results, added to the lower morbidity of amniocentesis compared with cordocentesis, might lead to cordocentesis being abandoned in the prenatal diagnosis of congenital toxoplasmosis.

Evaluation of the second generation IMx Toxo IgG antibody assay for detection of antibodies to Toxoplasma gondii in human sera.

For an evaluation of the Abbott IMx Toxo IgG second generation, antibodies to Toxoplasma gondii were detected by Abbott IMx Toxo IgG and IgM, Vidas Toxo IgG and Toxo IgM (bioMérieux, France) with immunofluorescence assay verified by the dye-test for IgG, and immunosorbent agglutination assay (ISAGA) for IgM as references. The study included 507 serum samples collected over one month in two laboratories, 32 samples from HIV-infected patients, and 70 serial samples from 23 women surveyed for seroconversion or persistent IgM. After exclusion of nine equivocal results from the 507 samples, the sensitivity and specificity, respectively, were 100% (156/156) and 100% (342/342) for the IMx Toxo IgG and 98.1% (153/156) and 100% (342/342) for the Vidas Toxo IgG. Of the 32 HIV-infected patient samples, 7 gave false positive results with IMx Toxo IgG. This was because the samples had been heated. In 5 of the 70 serial samples. IMx Toxo IgG gave positive results earlier than Vidas Toxo IgG and in two cases earlier than IgM antibody assays. In this study IMx Toxo IgG second generation showed an increase in sensitivity and specificity in comparison with data reported previously for the first generation.

[Congenital toxoplasmosis: contribution of postnatal biological follow-up]. / Toxoplasmose congénitale: apport du suivi biologique postnatal.

OBJECTIVES: The diagnosis of congenital toxoplasmosis includes a postnatal follow-up, often preceded by a prenatal diagnosis. The aim of our study was to assess the performances of the different techniques used and the value of the samples in the postnatal biological diagnosis. METHODS: The methods available between 1985 and 1993 consisted in the detection of: i) Toxoplasma gondii in the placenta; ii) anti-T. gondii IgM in infant's blood by enzyme-linked immuno-sorbent assay (ELISA), immuno-sorbent agglutination assay (ISAGA) and indirect immuno-fluorescence (IFI), and anti-T. gondii IgG by ELISA and IFI; and iii) neo-synthetized anti-T. gondii IgG and IgM by enzyme-linked immuno-filtration assay (ELIFA). RESULTS: Among 400 cases of seroconversion diagnosed during pregnancy, a sure diagnosis with complete follow-up could be established for 104 infants; 37 of them had proven congenital toxoplasmosis (CT+) while 75 had no congenital toxoplasmosis (CT-). Biological arguments supporting congenital toxoplasmosis had been observed as early as birth in 78.4% of CT+ cases and before two months in 94.6%. The serologic tests were positive in 88.2% of CT+ cases by ELIFA, in 73.0% by ISAGA, in 43.3% by ELISA M and in 14.0% by IFI M. ELIFA was the less specific method (91.3%). CONCLUSION: The sensitive techniques (ELIFA and ISAGA), were essential for the instant follow-up to detect toxoplasmic infection as early as birth.

A new set of primers for the detection of Toxoplasma gondii in amniotic fluid using polymerase chain reaction.

A new PCR system including a pair of primers, a probe and an internal control were designed from the B1 gene of Toxoplasma gondii. The system described allowed the detection of less than 10 tachyzoites of the RH strain of T. gondii. Among 21 amniotic fluid samples, this system diagnosed the cases of congenital toxoplasmosis which were simultaneously diagnosed using mice inoculation, in vitro culture, and serology from both amniotic fluid and fetal blood. These results show that these new primers allow for a highly sensitive detection of T. gondii DNA.

[Serodiagnosis of toxoplasmosis: a comparative multicenter study of a standard scale through various actual tests and expression of the results in international units. Groupe de travail toxoplasmose du Contrôle national de qualité en parasotologie. Syndicat des fabricants de réactifs de laboratoire. Groupe de travail standardisation des tests sérologiques du Réseau européen de lutte contre la toxoplasmose congénitale]. / Le sérodiagnostic de la toxoplasmose: etude comparative multicentrique d'une gamme étalon, par les différents tests actuels et avec expression des résultats en unités internationales. Groupe de travail toxoplasmose du Contrôle national de qualité en parasitologie, Syndicat des fabricants de réactifs de laboratoire, Groupe de travail standardisation des tests sérologiques du Réseau européen de lutte contre la toxoplasmose congénitale.

Reported are the results of a multicentre study involving 40 laboratories that was carried out in France to assess all the currently available methods used for the serodiagnosis of toxoplasmosis. For this purpose 10 batches of control sera were prepared with titres in the range 0-260 IU per ml. These sera were tested in nine laboratories using immunofluorescence methods; in three laboratories using dye tests; in forty laboratories using enzyme-linked immunosorbent assay; in four laboratories using direct agglutination and haemagglutination; in seven laboratories using the high-sensitivity IgG agglutination test; and in three laboratories using the latex agglutination test. In this way, 70 series of titrations were carried out using seven procedures and the results were compared with those obtained using the WHO reference serum in 15 cases, with the French national E6 serum in 16 other cases, and in 39 cases using 15 reference sera supplied by the reagent manufacturers. Rigorous comparison of the tests was not possible in all cases because one aim of the study was to ensure that the tests were carried out under the usual working conditions that prevailed in the participating laboratories. The results obtained indicate that the serological tests currently available for toxoplasmosis are acceptable for its serodiagnosis. Presentation of the titres in IU has advantages; however, caution is required since the definition of IU varies according to the test and reagents used. It is therefore essential that the conditions and limits for a positive reaction be carefully defined in each case, especially for commercially available kits.

Diagnosis of congenital toxoplasmosis by immunoblotting and relationship with other methods.

Immunoblot has been evaluated as a diagnostic method for congenital toxoplasmosis. Like enzyme-linked immunofiltration assay (ELIFA), immunoblot can be used to compare antibody patterns and to determine if the antibodies are transmitted by the mother or synthesized by the fetus or infant. Among the 48 infants tested, 27 had congenital toxoplasmosis and 21 were suspected but had none. Reproducibility, sensitivity, specificity, and positive predictive values in immunoblot for immunoglobulins (Igs) G+M+A and/or G+M were 90, 92.6, 89.1, and 92.4%, respectively. G+M immunoblot and G+M ELIFA have better sensitivities than the conventional IgM immunosorbent agglutination assay, IgM enzyme-linked immunosorbent assay (ELISA), IgM immunofluorescence antibody test, in vitro culture, and mouse inoculation. The novel antibodies, i.e., those synthesized by infants against Toxoplasma gondii, were of the IgG class in most cases, although a confident diagnosis could be related to the number of observed Ig classes (G+M, G+A, and G+M+A). Immunoblot has a better resolution than ELIFA. In prenatal diagnosis, immunoblot could be complementary to in vitro culture and mouse inoculation. In the other cases, early detection by immunoblot appears to give the best results when compared with the other serological methods.

[Evaluation of the Vidas system for the serological diagnosis of toxoplasmosis]. / Evaluation du système Vidas pour le diagnostic sérologique de la toxoplasmose.

The recent immuno-analysis system Vidas (bioMérieux) for the serological diagnosis of toxoplasmosis was compared to the Abbott Toxo EIA system, taking the indirect immunofluorescence assay (IFA) as reference for immunoglobulin G and the immunosorbent agglutination assay (ISAGA) for immunoglobulin M. Five hundred and ninety-four individual sera and 15 seroconversions or recent infections (39 sera) were studied. Sensitivity and specificity of the Vidas system were respectively 99.7% and 99.4% for IgG, and 100% and 97% for IgM. During primary toxoplasmia infection, the Vidas system allows very early detection of the appearance of IgM and IgG. The Vidas Toxo IgG is more sensitive than the Abbott G EIA. For IgM, the Vidas Toxo M is less specific but much more sensitive than the Abbott M EIA.