Globally diverse Toxoplasma gondii isolates comprise six major clades originating from a small number of distinct ancestral lineages

Abstract

Marked phenotypic variation characterizes isolates of Toxoplasma gondii, a ubiquitous zoonotic parasite that serves as an important experimental model for studying apicomplexan parasites. Progress in identifying the heritable basis for clinically and epidemiologically significant differences requires a robust system for describing and interpreting evolutionary subdivisions in this prevalent pathogen. To develop such a system, we have examined more than 950 isolates collected from around the world and genotyped them using three independent sets of polymorphic DNA markers, sampling 30 loci distributed across all nuclear chromosomes as well as the plastid genome. Our studies reveal a biphasic pattern consisting of regions in the Northern Hemisphere where a few, highly clonal and abundant lineages predominate; elsewhere, and especially in portions of South America are characterized by a diverse assemblage of less common genotypes that show greater evidence of recombination. Clustering methods were used to organize the marked genetic diversity of 138 unique genotypes into 15 haplogroups that collectively define six major clades. Analysis of gene flow indicates that a small number of ancestral lineages gave rise to the existing diversity through a process of limited admixture. Identification of reference strains for these major groups should facilitate future studies on comparative genomics and identification of genes that control important biological phenotypes including pathogenesis and transmission.

Population, genetic, and antigenic diversity of the apicomplexanEimeria tenellaand their relevance to vaccine development

“…Comparison of haplotype occurrence and diversity provided strong evidence of the expansion of a limited number of distinct haplotypes with significant LD in Northern India and North Africa, in contrast to Southern India and Nigeria, where no LD was detected. The limited haplotype diversity detected in the Northern regions partially resembles that described for the closely related coccidian T. gondii, for which a small number of dominant clonal genotypes have been described, supplemented by higher levels of genetic diversity in regions such as South America (35). However, comparison between these two genera reveals fundamental biological differences, including an apparently obligate requirement for sexual reproduction and a massive, regularly replaced, immunologically naive pool of potential definitive hosts (chickens) for Eimeria.…”

Anthropogenics: Human Influence on Global and Genetic Homogenization of Parasite Populations

“…The global diversity of Toxoplasma gondii is still far from complete, owing to sampling that underrepresents much of Asia and Africa (Sibley et al, 2009;Su et al, 2012). Nonetheless, this parasite has been subjected to enough sampling to warrant preliminary conclusions concerning the human role in shaping that diversity (Sibley et al, 2009).…”

Risk Factors, Pathogenesis and Diagnosis of Ocular Toxoplasmosis

“…Currently, it is assumed that the population of T. gondii consists of 3 3 predominant clonal lineages, which differ at the DNA sequence level by 1% or less [25] but microsatellite analysis has shown the high diversity of that genus [26]. In Europe and the United States, type II is the most common cause of systemic Toxoplasma infection [27].…”