Transmission of Leishmania donovani in the Hills of Eastern Nepal, an Outbreak Investigation in Okhaldhunga and Bhojpur Districts

Abstract

BackgroundIn the Indian subcontinent, Visceral leishmaniasis is endemic in a geographical area coinciding with the Lower Gangetic Plain, at low altitude. VL occurring in residents of hill districts is therefore often considered the result of Leishmania donovani infection during travel. Early 2014 we conducted an outbreak investigation in Okhaldhunga and Bhojpur districts in the Nepal hills where increasing number of VL cases have been reported.Methodology/Principal FindingsA house-to-house survey in six villages documented retrospectively 35 cases of Visceral Leishmaniasis (VL). Anti-Leishmania antibodies were found in 22/23 past-VL cases, in 40/416 (9.6%) persons without VL and in 12/155 (7.7%) domestic animals. An age- and sex- matched case-control study showed that exposure to known VL-endemic regions was no risk factor for VL, but having a VL case in the neighbourhood was. SSU-rDNA PCR for Leishmania sp. was positive in 24 (5%) of the human, in 18 (12%) of the animal samples and in 16 (14%) bloodfed female Phlebotomus argentipes sand flies. L. donovani was confirmed in two asymptomatic individuals and in one sand fly through hsp70-based sequencing.Conclusions/SignificanceThis is epidemiological and entomological evidence for ongoing local transmission of L. donovani in villages at an altitude above 600 meters in Nepal, in districts considered hitherto non-endemic for VL. The VL Elimination Initiative in Nepal should therefore consider extending its surveillance and control activities in order to assure VL elimination, and the risk map for VL should be redesigned.

Longitudinal Study of Transmission in Households with Visceral Leishmaniasis, Asymptomatic Infections and PKDL in Highly Endemic Villages in Bihar, India

“…Although these observations provide insight into VL transmission in highly endemic villages, further studies are needed to understand how the parasite reservoir is maintained in areas where there are very few VL cases, such as in the hilly regions of Nepal and Bhutan [25, 26], and why VL cases tend to cluster and occur in shifting and tightly localized areas. With respect to control measures, the results from this study argue that every effort should be made to identify and treat acute VL cases as soon as possible, since this appears to be the major source of transmission.…”

Elimination of visceral leishmaniasis on the Indian subcontinent

“…In Nepal 11 districts out of 75 are affected, all situated in the north eastern Terai region (7, 8). Recently however clusters of VL cases have also been reported from some of the hilly districts previously considered non-endemic, with evidence of local transmission (45). …”

Single locus genotyping to track Leishmania donovani in the Indian subcontinent: Application in Nepal

“…Based on these data we could show that particularly ISC001 has a different geographic distribution as compared to the other genotypes, and is present predominantly in hilly areas. This could be related to a local epidemic, which is corroborated by a recent outbreak investigation showing that transmission does take place at higher altitudes [20]. ISC001 is genetically very different from parasites belonging to the main population endemic in the Terai lowland, and shows different phenotypic features, hence its epidemiological follow-up is highly relevant.…”