Leishmaniases are severe diseases affecting humans and animals caused by protozoan parasites belonging to the Leishmania genus and transmitted by female sandflies' bites. These parasitoses are widespread over all continents, except Antarctica. Nowadays, leishmaniases still pose considerable public health problems. At present, it is suggested and even admitted that Leishmania species present a basically clonal population structure associated to rare sexual recombination events. However, such a statement mostly relies on population genetics studies that may be criticised. The markers used were little adapted (e.g. lack of resolution or dominant markers) and clonality was inferred from the analysis of linkage disequilibria across loci that are far from ideal in that respect. The principal objective of our work was to study the population structure and reproductive mode of Leishmania braziliensis species using microsatellite markers. This species is an important leismaniasis agent in South America. In total, 125 human isolates (56 from Peru and 69 from Bolivia) were genotyped on 12 microsatellite loci. Various population genetics tests were applied.
Results/Conclusions
The results obtained appear in contradiction with a simple clonal propagation. Indeed, strong homozygosities found at each locus, associated to strong linkage disequilibria across loci, advocated for an inbred reproductive strategy. Further analyses suggest that a significant part of the high heterozygote deficits observed in our samples is likely the consequence of a Wahlund effect, i.e. the coexistence of strongly differentiated genetic entities within each sample. This approach was also applied to other species of Leishmania to test for the generality of these findings. Then, it will be interesting to work on finer scale (samples collected the same year and in the same village), in order to circumscribe the strong structure observed (Wahlund effect). Finally, the debate on clonality/sexuality of these protozoa parasites is far from being solved and thus deserves further investigations. Such improved knowledge would indeed provide useful information for diagnostic, epidemiological inquiries and drug or vaccine elaborations.
