Can cutaneous leishmaniasis provoke a resurgence of kala-azar in the Indian subcontinent?

Abstract

Background: The ongoing kala-azar elimination program in Nepal is based on the assumption of anthroponotic transmission of the protozoan parasite Leishmania donovani. This parasite species was recently also found in lesions of cutaneous leishmaniasis (CL) cases, which are increasingly reported mainly from western Nepal. The question whether or not CL causing L. donovani can also contribute to VL is a crucial one to answer if the success of the VL elimination initiative in the Indian subcontinent is to be sustained, though evidence on sub-species level genomic differences between CL and VL causing L. donovani is currently lacking. This study aims to provide a genomic comparison of L. donovani parasites currently causing CL in Nepal with previously described L. donovani isolates.

Methods: A case series study was carried out in sentinel dermatological sites in Western Nepal. Skin punch biopsies were collected from clinically suspected CL lesions. Molecular tests based on the ribosomal RNA gene array were used to detect and characterize the Leishmania parasites.

Results: Leishmania parasites detected in 26 cutaneous leishmaniasis patients were identified as L. donovani. Importantly, their analyzed DNA sequences were identical, and shared with previously documented sequences from both cutaneous and visceral disease-causing parasites in Nepal, India and Bhutan.

Conclusions: Our study suggests that CL and VL are caused by similar if not identical L. donovani parasite strains, though additional sequencing is required to corroborate this finding. If confirmed, cutaneous lesions could act as a kala-azar parasite reservoir, which would have important implications for the kala-azar elimination program.

Keywords: Leishmania donovani; Cutaneous leishmaniasis; Genomic surveillance; Kala-azar elimination initiative; Nepal; Parasite characterization; Visceral leishmaniasis.

Fig. 1

rDNA-ITS1 based dendrogram from CL samples analyzed in this study, compared to previously documented sequences of the Indian subcontinent. The dendrogram was constructed by producing a guide tree file with the ClustalW algorithm (http://www.clustal.org/) and loading that as a user tree file in MEGA 7 (https://www.megasoftware.net/). The tree was rerooted in MEGA 7 for visualization purposes only. The dendrogram is based upon resemblance of the sequences by pairwise comparison. No global alignment was constructed, and no evolutionary model was implied. Hence, the branch order does not reflect evolutionary history. Each taxon is identified using the WHO strain identification system, followed by the GenBank accession number if available. In case sequences were not retrieved from GenBank, the source of the sequence information is mentioned on the right of the figure. CL and VL samples are labeled with different symbols and colors, as shown in the top left. For samples from Nepal, the district where the patient was presumably infected is shown at the end of the taxon identification. Indications on the right of the tree depict the country of origin of the sequenced parasites. Two sequences are representative for respectively 12 and 191 strains, as indicated in brackets. In the hybrid strain LdHPCL66, 2 different rDNA-ITS1 variants were identified, shown with an asterisk following the taxon identification

Fig. 2

Overview of geographical location of collaborating dermatological sites and district of patient residence for 26 skin samples from patients with cutaneous leishmaniasis analyzed in this study; seven CL samples from [5] and [11]; and four [VL] samples from Nepal [9, 10] and Bhutan [13]