Diagnosis of infection with Toxoplasma gondii in pregnant women, neonates and immunocompromised patients

Infection with Toxoplasma gondii poses unique diagnostic problems like long-term persistence of specific IgM-antibodies, which makes it difficult to use the presence of Toxoplasma-specific IgM-antibodies alone as a sign of acute infection. The importance of determining the time of infection in pregnant women is also a unique diagnostic challenge in Toxoplasma diagnostics.

The first paper in this thesis compares the performance of different enzyme immuno assays, immunofluorescence assays, immunosorbent agglutination assays and IgG-avidity assays. The study showed that a combination of an IgM assay followed by an IgG-avidity test was the best combination to estimate the time interval in which infection had taken place. Diagnosis of infection in newborns without Toxoplasma-specific IgM- or IgA antibodies is difficult and a two-dimensional immunoblot assay to distinguish between maternal and child IgG-antibodies with different specificities was developed having higher sensitivity than previous assays.

A new IgG-avidity assay based on recombinant antigens was developed, which effectively abolished the problem of long-term low IgG-avidity seen in samples analysed by assays using whole cell, lysed antigen. Enzyme immuno assays with whole cell, lysed antigen pose problems with poor discrimination between IgG negative and low-positive samples and recombinant antigens should provide assays with less background, however, the sensitivity may be reduced.

Two studies show how combinations of recombinant antigens perform in assays of Toxoplasma-specific IgG- and IgM-antibodies. The assays do not yet have the same sensitivity as whole cell, lysed antigen based assays, but the concept is promising and should be further explored. T. gondii infection is a problem in immunodeficient hosts as the parasite remains alive in the chronically infected.

Current strategies for diagnosing these infections rely on regular testing for Toxoplasma-specific DNA by PCR in blood and other fluids including bronchioalveolar lavage (BAL). We show that a new, real time PCR based assay can be used to detect Toxoplasma in BAL fluids from HIV patients.

List of scientific papers

I. Roberts A, Hedman K, Luyasu V, Zufferey J, Bessieres MH, Blatz RM, Candolfi E, Decoster A, Enders G, Gross U, Guy E, Hayde M, Ho-Yen D, Johnson J, Lecolier B, Naessens A, Pelloux H, Thulliez P, Petersen E (2001). Multicenter evaluation of strategies for serodiagnosis of primary infection with Toxoplasma gondii. Eur J Clin Microbiol Infect Dis. 20(7): 467-74.
https://pubmed.ncbi.nlm.nih.gov/11561802

II. Beghetto E, Buffolano W, Spadoni A, Del Pezzo M, Di Cristina M, Minenkova O, Petersen E, Felici F, Gargano N (2003). Use of an immunoglobulin G avidity assay based on recombinant antigens for diagnosis of primary Toxoplasma gondii infection during pregnancy. J Clin Microbiol. 41(12): 5414-8.
https://doi.org/10.1128/JCM.41.12.5414-5418.2003

III. Pietkiewicz H, Hiszczynska-Sawicka E, Kur J, Petersen E, Nielsen HV, Stankiewicz M, Andrzejewska I, Myjak P (2004). Usefulness of Toxoplasma gondii-specific recombinant antigens in serodiagnosis of human toxoplasmosis. J Clin Microbiol. 42(4): 1779-81.
https://doi.org/10.1128/JCM.42.4.1779-1781.2004

IV. Nielsen HV, Schmidt DR, Petersen E (2005). Diagnosis of congenital toxoplasmosis by two-dimensional immunoblot differentiation of mother and child immunoglobulin g profiles. J Clin Microbiol. 43(2): 711-5.
https://doi.org/10.1128/JCM.43.2.711-715.2005

V. Petersen E, Thalib L, Gras L, Paul M, Wallon M, Evengard B, Hayde M, Gilbert R for the European Multicentre Study on Congenital Toxoplasmosis (EMSCOT) (2005). Screening for congenital toxoplasmosis: accuracy of IgM and IgA tests after birth. [Submitted]

VI. Petersen E, Borobio MV, Guy E, Liesenfeld O, Meroni V, Naessens A, Spranzi E, Thulliez P (2005). European multicenter study of the LIAISON automated diagnostic system for determination of Toxoplasma gondii-specific immunoglobulin G (IgG) and IgM and the IgG avidity index. J Clin Microbiol. 43(4): 1570-4.
https://doi.org/10.1128/JCM.43.4.1570-1574.2005

VII. Petersen E, Edvinsson B, Benfield T, Lundgren B, Evengard B (2005). Diagnosis of pulmonary infection with toxoplasma gondii immunocompromised patients. [Manuscript]

VIII. Buffolano W, Baghetto E, Del Pezzo M, Spadoni A, Di Cristina M, Petersen E (2005). The use of recombinant antigens for the early postnatal diagnosis of congenital toxoplasmosis. [Submitted]