IFR 145 GEIST, EA 3174 NeuroEpidémiologie Tropicale et Comparée, Université de Limoges, Limoges, France.
PLoS Negl Trop Dis. 2010 Nov 2;4(11):e876. doi: 10.1371/journal.pntd.0000876.
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 FINDINGS: Seropositive 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.
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.
刚地弓形虫分布于世界各地，但各基因型在不同大陆的分布以及人类弓形虫病的临床表现存在差异。欧洲、北美和南美有多项研究表明，基因型在人类弓形虫病的临床表现中起一定作用。关于非洲刚地弓形虫分离株的遗传数据很少，不足以进行种群结构分析，而种群结构分析是更好地了解分布、循环和传播的基础。
方法/主要发现：对来自加蓬城乡地区的血清阳性动物进行刚地弓形虫分离和基因分型分析。通过生物测定法从小鼠中获得了 68 株分离株，其中包括 1 株混合感染（69 株）。使用位于 10 条不同染色体上的 13 个微卫星标记的长度多态性进行基因分型。根据贝叶斯统计建模、基于遗传距离的邻接树重建、F（ST）和连锁不平衡分析结果进行种群结构分析。检测到中等遗传多样性。3 个单倍群和 1 个单一基因型聚类了 27 个基因型。大多数菌株属于全世界 III 型对应的单倍群之一。其余菌株分布在 2 个单倍群（非洲 1 型和 3 型）和 1 个单一基因型中。分离时的小鼠毒力在单倍群间有显著差异。非洲 1 型单倍群的毒力最强。
提出非洲 1 型和 3 型单倍群是非洲循环的刚地弓形虫的新主要单倍群。讨论了与在中美洲和南美洲循环的菌株的可能联系。种群结构分析表明，在一个农村地区存在局部传播，在该国的主要城市之间存在菌株循环。这种由人类活动促进的循环可能导致遗传交换。首次使用微卫星标记的高鉴别力解决了西非刚地弓形虫种群的关键流行病学问题，为进一步的流行病学和临床研究奠定了基础。
