Abstract
BackgroundIt is increasingly recognized that climate change can alter the geographical distribution of vector-borne diseases (VBDs) with shifts of disease vectors to higher altitudes and latitudes. In particular, an increasing risk of malaria and dengue fever epidemics in tropical highlands and temperate regions has been predicted in different climate change scenarios. The aim of this paper is to expand the current knowledge on the seasonal occurrence and altitudinal distribution of malaria and other disease vectors in eastern Nepal.MethodsAdult mosquitoes resting indoors and outdoors were collected using CDC light trap and aspirators with the support of flash light. Mosquito larvae were collected using locally constructed dippers. We assessed the local residents’ perceptions of the distribution and occurrence of mosquitoes using key informant interview techniques. Generalized linear models were fitted to assess the effect of season, resting site and topography on the abundance of malaria vectors.ResultsThe known malaria vectors in Nepal, Anopheles fluviatilis, Anopheles annularis and Anopheles maculatus complex members were recorded from 70 to 1,820 m above sea level (asl). The vectors of chikungunya and dengue virus, Aedes aegypti and Aedes albopictus, the vector of lymphatic filariasis, Culex quinquefasciatus, and that of Japanese encephalitis, Culex tritaeniorhynchus, were found from 70 to 2,000 m asl in eastern Nepal. Larvae of Anopheles, Culex and Aedes species were recorded up to 2,310 m asl. Only season had a significant effect on the abundance of An. fluviatilis, season and resting site on the abundance of An. maculatus complex members, and season, resting site and topography on the abundance of An. annularis. The perceptions of people on mosquito occurrence are consistent with entomological findings.ConclusionsThis study provides the first vertical distribution records of vector mosquitoes in eastern Nepal and suggests that the vectors of malaria and other diseases have already established populations in the highlands due to climatic and other environmental changes. As VBD control programmes have not been focused on the highlands of Nepal, these findings call for actions to start monitoring, surveillance and research on VBDs in these previously disease-free, densely populated and economically important regions.
Highlights
It is increasingly recognized that climate change can alter the geographical distribution of vector-borne diseases (VBDs) with shifts of disease vectors to higher altitudes and latitudes
Mosquito species composition A total of 2,538 adult mosquitoes belonging to the four genera Aedes (10%), Anopheles (55%), Armigeres (6%) and Culex (29%) were collected in both seasons (Table 1)
The principal vector of lymphatic filariasis, C. quinquefasciatus, and the Japanese encephalitis virus vector Culex tritaeniorhynchus accounted for 12% and 31% of the total collected Culex mosquitoes (n = 742)
Summary
It is increasingly recognized that climate change can alter the geographical distribution of vector-borne diseases (VBDs) with shifts of disease vectors to higher altitudes and latitudes. 44 species of Anopheles mosquitoes have been identified in Nepal based on morphological characteristics but only seven have been reported as malaria vectors of primary importance [2,3]. These include: Anopheles minimus, Anopheles fluviatilis, Anopheles annularis, Anopheles maculatus, Anopheles dravidicus, Anopheles pseudowillmori, and Anopheles willmori [3]. It has been reported that deforestation and effective control using DDT practically eliminated An. minimus in Nepal during the 1960s [4], and An. fluviatilis is the primary malaria vector in Nepal, An. annularis the secondary malaria vector and the An. maculatus complex members are seasonal malaria vectors in the mountain region of Nepal [2,3,4,5,6]. Other Anopheles species from the group of 44 have been incriminated elsewhere in Asia [9,10,11] and may play a role in malaria transmission under changing environments and climate in Nepal [12]
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