Genetic structure and evolution of the Leishmania genus in Africa and Eurasia: what does MLSA tell us
Résumé
Leishmaniasis appears as a complex parasitic disease from taxonomic, clinical and epidemiological points of view. The role of the genetic exchanges is a highly debated question for over 20 years and their recent experimental demonstration along with the demonstration of interspecific hybrids in natura has revived this debate. After arguing that these exchanges were exceptional and were not contributing to the evolution of these protozoa, the current idea is that interspecific exchanges could be a major driving force, allowing rapid adaptation to new reservoirs and vectors, expansion into new parasitic cycles and adaptation to new life conditions. To assess the existence of gene flows between species in the course of evolution we have applied a MLSA-based approach to more than 220 Leishmania strains from Africa and Eurasia, which are supposed to represent the most accurately the genetic diversity of this genus. A remarkable congruence of the phylogenetic signal was observed and seven genetic clusters were evidenced, showing mainly independent lineages accumulating divergences without any sign of recent interspecific recombination. From a taxonomic point of view, the strong genetic structuration of the different species does not question the current classification, except for species causing visceral forms (L. donovani, L. infantum and L. archibaldi). Although these taxa cause different clinical forms and are maintained in different cycles, they are not clearly distinct and form a continuum, in line with the concept of species complex already suggested for this group thirty years ago. These results should have practical consequences regarding the molecular identification of parasites and the subsequent therapeutic management of Leishmaniases.
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