Additional Haplogroups of Toxoplasma gondii out of Africa: Population Structure and Mouse-Virulence of Strains from Gabon

Aurélien Mercier,Patrick Durand,Anne-Laure Bañuls,Daniel Ajzenberg,Bettina Salle,Henri Bonnabau,Marie-Laure Dardé,Barthélémy Ngoubangoye,Sébastien Devillard,Maria Yazdanbakhsh

doi:10.1371/journal.pntd.0000876

Abstract

Background Toxoplasma gondii is found worldwide, but distribution of its genotypes as well as clinical expression of human toxoplasmosis varies across the continents. Several studies in Europe, North America and South America argued for a role of genotypes in the clinical expression of human toxoplasmosis. Genetic data concerning T. gondii isolates from Africa are scarce and not sufficient to investigate the population structure, a fundamental analysis for a better understanding of distribution, circulation, and transmission.Methodology/Principal FindingsSeropositive animals originating from urban and rural areas in Gabon were analyzed for T. gondii isolation and genotyping. Sixty-eight isolates, including one mixed infection (69 strains), were obtained by bioassay in mice. Genotyping was performed using length polymorphism of 13 microsatellite markers located on 10 different chromosomes. Results were analyzed in terms of population structure by Bayesian statistical modeling, Neighbor-joining trees reconstruction based on genetic distances, F ST and linkage disequilibrium. A moderate genetic diversity was detected. Three haplogroups and one single genotype clustered 27 genotypes. The majority of strains belonged to one haplogroup corresponding to the worldwide Type III. The remaining strains were distributed into two haplogroups (Africa 1 and 3) and one single genotype. Mouse virulence at isolation was significantly different between haplogroups. Africa 1 haplogroup was the most virulent.Conclusion Africa 1 and 3 haplogroups were proposed as being new major haplogroups of T. gondii circulating in Africa. A possible link with strains circulating in South and Central America is discussed. Analysis of population structure demonstrated a local spread within a rural area and strain circulation between the main cities of the country. This circulation, favored by human activity could lead to genetic exchanges. For the first time, key epidemiological questions were addressed for the West African T. gondii population, using the high discriminatory power of microsatellite markers, thus creating a basis for further epidemiological and clinical investigations.

Highlights

Toxoplasma gondii is a worldwide haploid protozoan parasite, and distribution of its genotypes varies across the continents (e.g. [1])
Africa 1 and 3 haplogroups were proposed as being new major haplogroups of T. gondii circulating in Africa
Analysis of population structure demonstrated a local spread within a rural area and strain circulation between the main cities of the country

Summary

Introduction

Toxoplasma gondii is a worldwide haploid protozoan parasite, and distribution of its genotypes varies across the continents (e.g. [1]). In tropical regions of South America, T. gondii strains are highly divergent from those of Europe or North America and display a high degree of genetic diversity [4,5,6,7]. Distinct isolates are found in different regions of South America [11]. Different from the three classical Types, may circulate on this continent [5] with some atypical genotypes highly pathogenic to humans [6]. Toxoplasma gondii is found worldwide, but distribution of its genotypes as well as clinical expression of human toxoplasmosis varies across the continents. Several studies in Europe, North America and South America argued for a role of genotypes in the clinical expression of human toxoplasmosis. Genetic data concerning T. gondii isolates from Africa are scarce and not sufficient to investigate the population structure, a fundamental analysis for a better understanding of distribution, circulation, and transmission

Methods

Results

Discussion

Conclusion