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Several studies reported that certain T. gondii genotypes and clonal lineages correlate with severe toxoplasmosis in mice and humans. Therefore it may be important to have information on the prevalence of different T. gondii genotypes in humans and animals.
In future, this information may help to better estimate the risk of infection for humans and animals. Information on the genotype of T. gondii an individual human or animal is infected may allow to conclude on the further development of disease and to optimise treatment. The results of studies summarized in this cumulative thesis demonstrate that a peptidemicroarray assay can be used for diagnosis of T. gondii infection and to detect T. gondii clonal type-specific antibody responses in seropositive humans and cats. With a peptide microarray and sera from experimentally-infected and naturally-infected cats it was shown for the first time that cats are able to mount a clonal type-specific IgG antibody response against T. gondii. After validation, 27 peptides were selected which were suitable for T. gondii serotyping in cats. Previous work suggested that individuals in the study area were mainly exposed to T. gondii clonal type II. However, there was no information, which clonal type of T. gondii is most prevalent in infected humans, and there was only limited data about the distribution of T. gondii types in cats in Germany. The results of this study demonstrate that positive peptide reactions presenting clonal type II were statistically significantly overrepresented in the tested human and cat population. The intensity, by which type II peptides were recognized, was also significantly higher than the intensity with which peptides of other specificities were detected. The results suggest that most T. gondii infections in humans and cats were caused by T. gondii clonal type II in Germany and confirmed previous findings reporting a pre-dominance of type II in oocysts shed by cats in Germany. Since sporulated T. gondii oocysts present one of the most important sources of infection for intermediate hosts, it was expected that there were no major differences in serotyping results between those for cats and humans.
These are the first peptide microarray-based serotyping studies on T. gondii infections in humans in Germany and the first in cats worldwide. However, further carefully validated typespecific peptides are necessary to optimize the specificity of serotyping. Further validation with a larger number of well-characterized sera may help to identify and select further polymorphic peptides with a diagnostic potential. The results summarized in the present thesis (publication 2, manuscript 3) demonstrate that propensity scale-based and ABCpred bioinformatic methods are suitable for the in-silico prediction of linear epitopes on T. gondii antigens. The propensity scale method identified nine polymorphic epitopes that could be used as part of a peptide panel for T. gondii serotyping in cats. Using ABCpred, eight novel linear epitopes were predicted, which could be included in a larger peptide array for diagnosis. A total of ten peptides with diagnostic potential (eight ABCpred-predicted and two taken from the literature) were identified in this study (publication 2). The use of these peptides in a peptide-array revealed an overall diagnostic sensitivity of 69% and a diagnostic specificity of 84%. These diagnostic parameters are acceptable, but not optimal. To achieve better diagnostic properties, it is necessary to identify further epitopes with diagnostic potential to extend the peptide panel.
In conclusion, this study demonstrates that bioinformatic programs in combination with peptide-microarray represent a powerful tool for the prediction and analysis of T. gondii linear epitopes suitable for serotyping or diagnosis. Based on peptides containing these epitopes peptide-microarray tests were developed in the present thesis and applied or serological typing of T. gondii infections in humans and cats.