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

摘要

Infection with Toxoplasma gondii poses unique diagnostic problems likelong-term persistence of specific IgM-antibodies, which makes itdifficult to use the presence of Toxoplasma-specific IgM-antibodies aloneas a sign of acute infection. The importance of determining the time ofinfection in pregnant women is also a unique diagnostic challenge inToxoplasma diagnostics. The first paper in this thesis compares theperformance of different enzyme immuno assays, immunofluorescence assays,immunosorbent agglutination assays and IgG-avidity assays. The studyshowed that a combination of an IgM assay followed by an IgG-avidity testwas the best combination to estimate the time interval in which infectionhad taken place. Diagnosis of infection in newborns without Toxoplasma-specificIgM- or IgA antibodies is difficult and a two-dimensional immunoblotassay to distinguish between maternal and child IgG-antibodies withdifferent specificities was developed having higher sensitivity thanprevious assays. A new IgG-avidity assay based on recombinant antigenswas developed, which effectively abolished the problem of long-term lowIgG-avidity seen in samples analysed by assays using whole cell, lysedantigen. Enzyme immuno assays with whole cell, lysed antigen poseproblems with poor discrimination between IgG negative and low-positivesamples and recombinant antigens should provide assays with lessbackground, however, the sensitivity may be reduced. Two studies show howcombinations of recombinant antigens perform in assays of Toxoplasma-specificIgG- and IgM-antibodies. The assays do not yet have the same sensitivityas whole cell, lysed antigen based assays, but the concept is promisingand should be further explored. T. gondii infection is a problem inimmunodeficient hosts as the parasite remains alive in the chronicallyinfected. Current strategies for diagnosing these infections rely onregular testing for Toxoplasma-specific DNA by PCR in blood and otherfluids including bronchioalveolar lavage (BAL). We show that a new, realtime PCR based assay can be used to detect Toxoplasma in BAL fluids fromHIV patients.