Leishmania (Leishmania) infantum zymodeme MON-1 is responsible for the majority of visceral leishmaniasis cases around the Mediterranean basin, albeit that it causes also cutaneous forms. The MON classification is based on starch gel multilocus enzyme electrophoresis (MLEE) typing. The aim of this work was to explore further the genetic diversity and phylogenetic status of this zymodeme by alternative typing techniques. Fourteen L. (L.) infantum/L. (L.) chagasi stocks identified as MON-1 by MLEE in reference laboratories, 3 L. infantum stocks attributed to other zymodemes (MON-24, MON-29, MON-33) and reference standard stocks belonging to other species (L. (L.) major, L. (L.) tropica and L. (L.) donovani) were characterized by 2 different markers: MLEE on cellulose acetate plates and Random Amplified Polymorphic DNA (RAPD). We have obtained 10 different genotypes with RAPD and 6 different genotypes with MLEE on cellulose acetate plates for the 14 L. infantum/L. chagasi MON-1 stocks studied. MLEE and RAPD data gave quite congruent phylogenetic results: L. infantum zymodeme MON-1 was shown to be polyphyletic and genetically heterogeneous. This work confirms the necessity of using different markers to build up a robust phylogeny. Finally the epidemiological and clinical implications of these results are discussed.

A set of 434 Trypanosoma cruzi stocks from a wide ecogeographical range was analysed by Multilocus Enzyme Electrophoresis for 22 genetic loci. Strong linkage disequilibrium, not associated with geographical distance, and 2 main genetic clusters each considerably heterogeneous, was observed. These results support the hypotheses previously proposed that T. cruzi natural populations are composed of highly diversified genetic clones distributed into 2 main phylogenetic lineages: lineage 1, the most ubiquitous in the endemic area, was more frequently observed in sylvatic cycles, whereas lineage 2, predominant in humans and domestic cycles, in the southern part of the area surveyed, was further partitioned into 5 lesser genetic subdivisions. T. cruzi appears therefore subdivided into at least 6 ‘discrete typing units’ or DTUs (Tibayrenc, 1998a–c). We have identified various specific isoenzyme markers (‘tags’; Tibayrenc, op. cit.) suitable for the routine identification of these DTUs for epidemiological tracking purposes. We discuss the correspondence with previous classifications and with the recent recommendations of the 90th anniversary of the discovery of Chagas disease symposium, as well as the impact of T. cruzi genetic variability on this parasite's biomedical diversity.