Molecular epidemiology and evolutionary genetics of Leishmania parasites

In order to illustrate the relevance of the concepts and methods of evoluti onary genetics in the understanding of the epidemiology of pathogenic agent s, we develop in this paper the case of the Leishmania, a genus of parasiti c protozoa. An extensive study of various natural populations of Leishmania in different countries (Old and New World) was carried out by using Multil ocus Enzyme Electrophoresis (MLEE) and Random Amplified Polymorphic DNA fin gerprinting (RAPD) as genetic markers. The data have been interpreted in ev olutionary genetic terms. The main benefit of this approach has been to bet ter define the concept of species in the genus Leishmania, on rigorous phyl ogenetic bases. As a matter of fact, a sound taxonomical background is a pr erequisite for any epidemiological approach. Since the biological concept o f species is difficult or impossible to apply for most pathogenic microorga nisms, we recommend relying on criteria of both phylognetic discreteness an d of epidemiological/medical relevance to describe new species of Leishmani a. Through this approach, fbr example, we have shown that the species statu s of L. (V.) peruviana can be supported. On the contrary; we have been unab le to clearly distinguish L. (V.) panamensis from L. (V.) guyanensis with g enetic tools. Additionally, we have shown that the epidemiological inferenc es based on a limited set of genetic markers can be misleading. As a matter of fact, we have demonstrated that a collection of L. (L.) infantum stocks identified, as zymodeme 'MON 1' by other authors present additional geneti c heterogeneity and do not correspond to a. distinct 'Discrete Typing Unit' DTU, and are actually polyphyletic. Lastly, in the samples that were conve niently designed, we have confirmed that Leishmania parasites have a basica lly clonal population structure. As the clonal model specifies it, occasion al bouts of genetic exchange remain nevertheless possible. Telling comparis ons are drawn with the evolutionary genetics of other pathogens Typanosoma cruzi and Trypanosoma congolense. (C) 1999 Australian Society for Parasitol ogy Inc. Published by Elsevier Science Ltd. All rights reserved.