Background: Kala-azar is a serious health problem in India. The situationhas worsened further due to the occurrence of cases unresponsive to antimonials. About 30-50% patientsdo not respond to the prevailing regimen of antimonials. The etiological agent for Indian kala-azar haslong been known to be Leishmania donovani. Recently, in a somewhat startling report, it was claimed thatL. Tropica causes nearly 25% of current kala-azar cases in India. It was also suggested that this mightbe in some way related to the unresponsiveness to pentavalent antimonials in the field. Material/Methods:Two independent molecular characterization techniques, multilocus enzyme electrophoresis (MLEE) and RAPD-PCR,were employed to analyze 15 clinical isolates from confirmed Indian kala-azar patients collected fromthe eastern part of the country over a period of nearly 20 years. The collection included six Sb(5+)-unresponsiveand one PKDL case. Results: Our observations strongly suggest that all the clinical isolates, includingthe antimony (Sb(5+))-unresponsive and PKDL ones, we studied were identical to the WHO reference strain(DD8) for Leishmania donovani by both the above methods and no strain variation might have occurred intwo major epidemic and inter-epidemic periods. We also observed that none of the Sb(5+)-unresponsivestains we analyzed was related to L. Tropica. Conclusions: We conclude that L. Donovani may be the causalagent for Indian kala-azar and that L. Tropica is most likely not an etiological agent for Indian Kala-azarcases that are unresponsive to antimonials.

Keywords: Bone Marrow - parasitology, DNA Primers, Drug Resistance, Electrophoresis, Cellulose Acetate, India, Isoenzymes - genetics, Leishmania donovani - enzymology, Leishmania donovani - genetics, Leishmania donovani - isolation & purification, Leishmania tropica - enzymology, Leishmania tropica - genetics, Leishmania tropica - isolation & purification, Leishmaniasis, Visceral - diagnosis, Leishmaniasis, Visceral - genetics, Leishmaniasis, Visceral - parasitology, Random Amplified Polymorphic DNA Technique, Spleen - parasitology, Bone Marrow - parasitology, DNA Primers, Drug Resistance, Electrophoresis, Cellulose Acetate, India, Isoenzymes - genetics, Leishmania donovani - isolation & purification, Leishmania tropica - isolation & purification, Leishmaniasis, Visceral - parasitology, Random Amplified Polymorphic DNA Technique, Spleen - parasitology