Detection and identification of old world Leishmania by high resolution melt analysis

Abstract

Background: Three major forms of human disease, cutaneous leishmaniasis, visceral leishmaniasis and mucocutaneous leishmaniasis, are caused by several leishmanial species whose geographic distribution frequently overlaps. These Leishmania species have diverse reservoir hosts, sand fly vectors and transmission patterns. In the Old World, the main parasite species responsible for leishmaniasis are Leishmania infantum, L. donovani, L. tropica, L. aethiopica and L. major. Accurate, rapid and sensitive diagnostic and identification procedures are crucial for the detection of infection and characterization of the causative leishmanial species, in order to provide accurate treatment, precise prognosis and appropriate public health control measures.

Methods/principal findings: High resolution melt analysis of a real time PCR product from the Internal Transcribed Spacer-1 rRNA region was used to identify and quantify Old World Leishmania in 300 samples from human patients, reservoir hosts and sand flies. Different characteristic high resolution melt analysis patterns were exhibited by L. major, L. tropica, L. aethiopica, and L. infantum. Genotyping by high resolution melt analysis was verified by DNA sequencing or restriction fragment length polymorphism. This new assay was able to detect as little as 2-4 ITS1 gene copies in a 5 microl DNA sample, i.e., less than a single parasite per reaction.

Conclusions/significance: This new technique is useful for rapid diagnosis of leishmaniasis and simultaneous identification and quantification of the infecting Leishmania species. It can be used for diagnostic purposes directly from clinical samples, as well as epidemiological studies, reservoir host investigations and vector surveys.

Figure 1. High resolution melting curves.

High resolution melting (HRM) curves of the 265–288 bp ITS1-PCR amplicon of Old World Leishmania species. Normalized fluorescence is plotted against degrees C° (deg.). The curves include parasites from different hosts and geographic origins including 7 strains of L. major, 5 of L. aethiopica, 7 of L. tropica, 13 of L. infantum and 2 of L. donovani.

Figure 2. High resolution melting curves of Old World Leishmania species compared with non-leishmanial trypanosomatids.

High resolution melting (HRM) curves for the ITS1-PCR amplicon from Old World Leishmania species [L. major (MHOM/TM/1973/5ASKH), L. infantum (MHOM/TN/1980/IPT1), L. donovani (MHOM/IN/1980/DD8), L. tropica (ISER/IL/2002/LRC-L909) and L. aethiopica (MHOM/ET/1972/L102)] and the non-leishmanial trypanosomatids Trypanosoma brucei, T. cruzi, T. equinum and Crithidia fasciculata. Normalized fluorescence is plotted against degrees C° (deg.).

Figure 3. High resolution melting curves of Leishmania tropica strains belonging to two microsatellite clusters in different regions of Israel.

Main part of the figure shows HRM plots of Leishmania species found in Israel (L. major, L. infantum and L. tropica). Insert is a magnification of the HRM region allowing differentiation between L. tropica strains belonging to microsatellite cluster IV (North Sea of Galilee) and microsatellite cluster I (central and southern Israel).