Study of Population Diversity of Toxoplasma gondii

Toxoplasma gondii, the causal agent of toxoplasmosis, is an important water and food borne protozoan parasite. T. gondii was previously shown to have a distinct clonal population structure composed of Type I, II and III lineages in North America and Europe. But more recent studies demonstrated high diversity in South America. In the present project we have conducted an intensive study of the population diversity of T. gondii and surveyed the extent of genetic variation among natural T. gondii isolates on a global scale in order to better understand the population dynamics and pathogenesis of this parasite. To this end, 948 T. gondii isolates have been collected from a broad range of animal hosts and different sites worldwide. Our initial multilocus PCR-RFLP genotyping analysis revealed high diversity (~140 distinct genotypes) with abundant unique genotypes in South America and a strong clonal population structure in North America, Europe, Asia and Africa. It also showed that the Type II is the most common lineage worldwide, followed by the type III strain. The Type I strain, though widely distributed, has been infrequently isolated. Several new clonal genotypes have been identified from South America. The newly identified 140 RFLP genotypes have been further analyzed by multilocus microsatellites and intron sequencing methods. The composite data set identified 11 different haplotypes, providing a framework for future study of molecular epidemiology and population genetics of T. gondii . Multilocus DNA sequencing of markers from each of the 14 chromosomes covering the entire genome has also been completed to help reveal more information about genome evolution and the origin of T. gondii . Taken together, this comprehensive epidemiological and population genetic study has revealed significant details on the diversity and extent of sexual recombination, which provides the basis for future studies to understand transmission patterns, population dynamics and origin of this successful apicomplexan parasite Toxoplasma gondii.