Isolation and characterization of Toxoplasma gondii isolates from human congenital toxoplasmosis cases reveal a new virulent genotype in São Paulo, Brazil.

Toxoplasma gondii causes severe disease in congenitally infected fetuses. The severity of fetal infection is related to the gestational stage at the time of maternal infection, parasite burden, and genotypic characteristics. South America has a high incidence of congenital toxoplasmosis and has the highest genotypic diversity of the parasite. In Brazil, clinical toxoplasmosis in children is notorious, however there are very limited data regarding the strains recovered from congenital infections. In this study, T. gondii strains from two cases of severe congenital toxoplasmosis from the São Paulo metropolitan area were isolated (TgHumIMTBr2 and TgHumIMTBr3) and biologically and molecularly characterized using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and microsatellite analysis, revealing a new non-archetypal virulent genotype designated as #318. The other isolate, genotype #175, has already been described in domestic and wild animals in Brazil, but is now associated with acute toxoplasmosis in humans. These data reinforce the role of non-archetypal T. gondii genotypes in the severity of human congenital toxoplasmosis, highlighting the importance of studies focused on parasite isolation and genotyping for a better understanding of the virulence of isolates from human toxoplasmosis and contributing to the knowledge of the diversity of T. gondii in Brazil.