Leishmania (Sauroleishmania): A Comment on Classification

Abstract

The classification of the Leishmania-like parasites of lizards has recently become the subject of sectional interests. In the absence of any objective criteria for classifying the group, two nomenclatures have come into current usage. Workers with interests in the natural history of the lizard parasites have emphasized the features that distinguish lizard and mammalian parasites and have tended to give the lizard parasites generic rank as the Sauroleishmania[1xSee all References][1]. Molecular biologists who have used the lizard parasites as a model organism have retained the lizard parasites within the genus Leishmania[2xPreviato, J.O. et al. Glycobiology. 1997; 7: 687–695Crossref | PubMed | Scopus (17)See all References][2].A number of studies, based on rRNA sequence comparisons, have been unable to resolve the phylogenetic relationship between the lizard parasite L. tarentolae and the mammalian Leishmania species[3xMarche, S. et al. Mol. Biochem. Parasitol. 1995; 71: 15–26Crossref | PubMed | Scopus (39)See all References][3]. However, two recent papers have provided the first DNA-based evidence that establishes the genetic relationships between the major groups of Leishmania species[4xNoyes, H.A. et al. J. Eukaryot. Microbiol. 1997; 44: 511–517Crossref | PubMed | Scopus (43)See all References, 5xCroan, D.G., Morrison, D.A., and Ellis, J.T. Mol. Biochem. Parasitol. 1997; 89: 149–152Crossref | PubMed | Scopus (121)See all References]. These studies present evidence from the RNA polymerase II, the DNA polymerase alpha and the small subunit rRNA genes and kinetoplast minicircles and they show that the lizard parasites diverged from the lineage leading to the L. (Leishmania) subgenus after this group separated from the New World parasites of the L. (Viannia) subgenus. This significant body of DNA evidence is inconsistent with a generic status for the lizard parasites but is consistent with acceptance of the subgenus L. (Sauroleishmania) as originally proposed by Saf'janova in 1982 (Ref. [1xSee all References][1]). Although the Leishmania-like parasites of the lizard gut were not included in these studies, there is already evidence to suggest that the lizard gut parasites are not close relatives of the lizard blood parasites and should not be included within the L. (Sauroleishmania), whatever taxonomic rank that group may have[1xSee all References][1].The correct classification of the lizard Leishmania is important. If these parasites are placed in a separate genus, there is a risk that they will be disregarded as an academic curiosity. If, as the available evidence suggests, they are derived from mammalian parasites, then the existing studies have real relevance to our understanding of the species that are human pathogens and there is a strong case for further work. The lizard parasites provide a useful model organism for studies of the molecular biology and biochemistry of the whole genus Leishmania, because they can be maintained in the laboratory with little risk to humans. Comparative studies of the lizard and mammalian parasites may shed further light on the mechanisms of the host–parasite relationship within the whole genus. Including the lizard parasites within the genus Leishmania should also prompt studies on the impact of these parasites on the epidemiology of the mammalian disease, since there is evidence of crossreactivity between lizard and mammalian parasite antigens in humans[1xSee all References][1].We urge parasitologists to adopt the subgenus L. (Sauroleishmania) Saf'janova, 1982, Ovezmukhammedov (1991)[1xSee all References][1] as the appropriate rank for the Leishmania from the blood of lizards and we look forward to the studies prompted by the renewed use of this designation.