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Parasite. 2020;27:7. doi: 10.1051/parasite/2020006. Epub 2020 Feb 7.

Serological diagnosis of Toxoplasma gondii: analysis of false-positive IgG results and implications.

Author information

1
Service de Parasitologie-Mycologie, CHU de Nice, Université Côte d'Azur, 06202 Nice, France - Inserm U1065, C3M, 06204 Nice, France.
2
Service de Parasitologie-Mycologie, CHU de Toulouse, 31300 Toulouse, France - PharmaDev, IRD UMR 152, Université de Toulouse, 31062 Toulouse, France.
3
Service de Microbiologie, Hôpital La Source, CHR d'Orléans, 45100 Orléans, France.
4
Parasitologie-Mycologie, CHU de Nantes, 44093 Nantes, France - Université de Nantes, Nantes Atlantique Universités, EA1155-IICiMed, Institut de Recherche en Santé 2, 44200 Nantes, France.
5
Institut de Parasitologie et de Pathologie Tropicale, EA 7292, Fédération de Médecine Translationnelle, Université de Strasbourg, 67000 Strasbourg, France.
6
EA7510, ESCAPE, Laboratoire de Parasitologie-Mycologie, Université de Reims Champagne-Ardenne, SFR Cap Santé FED 4231, 51096 Reims, France.

Abstract

in English, French

BACKGROUND:

Primary infection by Toxoplasma gondii in pregnant women can result in serious outcomes for the foetus. A false-positive IgG result during pregnancy can lead to a misdiagnosis of past infection and to stopping preventive measures. We collected 189 sera with positive Architect® Toxo IgG assay (Abbott Laboratories) and negative IgG results with at least two other serological tests, in order to find an explanation for the suspected false-positive IgG results. We used the recomLine Toxoplasma IgG® immunoblot (Mikrogen Diagnostik) to search for specific antigenic reactivities of the sera, and the LDBio Toxo II IgG® immunoblot (LDBio Diagnostics) as a confirmatory test.

RESULTS:

The bands GRA8 and/or GRA7 were positive for 148 samples (78.3%). GRA8 was the most frequent band, appearing in 133 patterns (70.4%), whereas GRA7 was present for 49 samples (25.9%). Of the 81 samples tested with LDBio®, 23 (28.4%) turned out to be positive. Of the 58 negative LDBio® tests (71.6%) (real false-positive Architect® IgG), 23 samples (39.6%) did not show either a GRA8 or p30 band by recomLine®. Their false positivity with Architect® remains unexplained since Abbott uses these two recombinant antigens for their assay.

CONCLUSIONS:

The Architect® IgG false positivity for T. gondii seems to be due to reactivity against GRA8 for the majority of the sera and GRA7 to a lesser extent. The hypothesis of past contact with parasites genetically close to T. gondii such as Hammondia hammondi or Neospora caninum seems promising and should be assessed further.

KEYWORDS:

Architect; False-positive; IgG; Serology; Toxoplasma gondii; Toxoplasmosis

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