In vitro differential phenotypic characteristics among Type-II Toxoplasma gondii strains from congenital toxoplasmosis in humans.

In France, more than 80% of human congenital toxoplasmosis is attributable to Toxoplasma gondii strains belonging to the type-II lineage, whereas 3 main lineages have been described in Europe. Cell invasion, parasite replication, and cyst formation of type-II strains isolated from congenital infections were compared in a human cell model. The phenotype patterns of the 4 type-II strains studied differed from each other; the 2 strains responsible for asymptomatic infection formed significantly fewer cysts than the 2 strains isolated from symptomatic toxoplasmosis. The capacity to form cysts was different among the type-II strains studied and may be related to the clinical form.