Geographical distribution of Toxoplasma gondii genotypes in Asia: A link with neighboring continents.

Defining the pattern of genetic diversity of Toxoplasma gondii is important to understand its worldwide distribution. During the last decades, a large number of studies have been published on Toxoplasma genotypes circulating in Europe, in North and South America. Two continents are still largely unexplored, Africa and, to a less extent, Asia. In this last continent, an increasing number of publications reported genotypes circulating in diverse provinces of China, but very few data are available for other Asian countries. After a systematic database search, 47 papers related to T. gondii genotypes in Asia were analyzed. Genetic characterization of DNA was performed by microsatellite markers, or more usually by a multiplex PCR using 11 PCR-RFLP markers, allowing data comparison to draw a first global picture of the population structure of this parasite throughout Asia. Overall, 390 isolates or DNA extracts were completely typed by PCR-RFLP and/or microsatellite marker methods, revealing 36 different PCR-RFLP or equivalent microsatellite genotypes: 15 genotypes identified by a ToxoDB number and 21 atypical or unique genotypes. The most common genotype found in Asia is the genotype ToxoDB#9 (Chinese 1). The clonal types I, II and II variant, and III were also commonly found in Asia. The geographical distribution of these genotypes across Asia may reflect either a continuum with Europe for the western part of Asia (presence of Type II), or the circulation of strains through animal migration or human activities between Africa and the Southwestern part of Asia (Africa 1 genotype in Turkey or ToxoDB#20 both I Sri-Lanka and in Ethiopia or Egypt). Although there are some indications of a genetic population structure in Southeast Asian countries different from the rest of Asia, more studies in this tropical part of Asia will be necessary for a region which represent as well as Africa one of the missing links of the T. gondii genetic diversity.