Molecular evidence for the importation of Old World Leishmania into the Americas.

A brief review of work carried out by the laboratory on the systematics of trypanosomatids during the last three years is given. The principal line of research has been on the taxonomy of New World Leishmania and one of the topics studied has been the determination of the autochthonous origin of certain Leishmania species found in the New World. Controversy exists as to whether the etiological agent of American Visceral Leishmaniasis is indigenous. Here, we present evidence from enzyme electrophoresis and schizodeme analysis indicating that L. chagasi has a recent origin and that it is similar to L. infantum. We also describe L. major-like isolates which have been found in the New World and present evidence suggesting that some of these populations may have been imported into the Americas. Reference strains from the subgenus Viannia are examined and compared with other Old World and New World species by enzyme electrophoresis. The results are analyzed numerically and we show that the Viannia species are a group of parasites indigenous to the New World that cluster separately from other Leishmania species. The numerical analyses also indicate that the subgenus forms a monophyletic group in contrast to the subgenus Leishmania which appears to be polyphyletic.