Genetic study of Toxoplasma gondii strains isolated from humans and animals

Abstract

Toxoplasma gondii is responsible for toxoplasmosis, a zoonosis spread worldwide. This PhD thesis aimed to provide a more comprehensive overview of the genetic characteristics and virulence of T. gondii strains isolated from humans and animals in Portugal. We enrolled T. gondii strains collected from intermediary (farm, urban and sylvatic animals) and the definitive (cat) hosts, as well as from human toxoplasmosis. In general, we applied Sag2 and microsatellites classical genotyping, next-generation sequencing and inoculation in mice. As major results, we highlight: i) the majority of isolated strains were avirulent in mice bioassay, where virulent strains belonged almost exclusively to Sag2 type I; ii) type II strains were the most identified type in strains from human toxoplasmosis as well as from all animal species, followed by type I strains; iii) this is the first report that shows type II T. gondii strains isolated from cattle, boars, foxes and hares in north of Portugal and recombinant strains isolated both from infected cats and pigeons; iv) the development of a rapid multi-loci-based NGS scheme, which allowed evaluating multi loci polymorphism and genomic mosaicism simultaneously. This schema is now implemented as the surveillance tool in the National Reference Laboratory of Parasitic and Fungal Infections (URSZ-INSA) to perform molecular surveillance of T. gondii; v) with this extended typing scheme, we identified a high rate (63 %) of recombinant strains isolated from humans, which had been previously identified as type I and II, as well as new putative genetic markers of virulence. Overall, this PhD shed some light on the genetic and virulence diversity of T. gondii strains circulating in Portugal and revealed a surprising scenario of rampant genomic exchange in this parasite. These data highlight the need for further extended genomic studies to better understand the genotype/phenotype associations in this important human pathogen and thus contribute to better infection control measures.