Abstract
BackgroundThe expansion of dengue vectors from lowland plains to the upland hilly regions of Nepal suggests the likelihood of increased risk of dengue. Our objective was to assess the effects of meteorological variables on vector indices and populations of dengue vectors in two different ecological regions of Nepal. An entomological survey was conducted in Kathmandu and Lalitpur (upland) and Chitwan (lowland) of Nepal in three different seasons from July 2015 to May 2016. The effect of meteorological variables on vector indices (house index, container index and Breteau index) and Aedes spp. population abundance was analyzed. A gamma regression was used to fit the models for vector indices and a negative binomial regression was used to model Aedes spp. population abundance.ResultsMonsoon season showed higher values for vector indices and vector populations compared to post-monsoon and pre-monsoon. Overall, the factor temperature-rainfall effect had a more significant influence on vector indices compared to relative humidity. The regression models showed that relative humidity has a greater impact in Chitwan than in Kathmandu. Variation was observed in the effect of predictor variables on Aedes aegypti and Ae. albopictus abundance.ConclusionsTemperature and rainfall contribute to the vector indices in the upland hilly region while relative humidity contributes in the lowland plains. Since vector prevalence is not only linked to meteorological factors, other factors such as water storage practices, waste disposal, sanitary conditions and vector control strategy should also be considered. We recommend strengthening and scaling up dengue vector surveillance and control programmes for monsoon season in both upland and lowland regions in Nepal.
Highlights
The expansion of dengue vectors from lowland plains to the upland hilly regions of Nepal suggests the likelihood of increased risk of dengue
breeding preferences ratio (BPR) value of metal drum container was highest in Chitwan. These results show that metal and glass containers are suitable breeding habitats for Aedes spp. and these containers should be monitored with equal priority during vector surveillance
The prevalence of Aedes larvae in monsoon and the more significant effect of monsoon season on HI_1, CI_1, BI_1 and Ae. aegypti abundance revealed in this study suggest that the existing practice of vector control during the time of outbreaks may not be sufficient for the effective management of vectors
Summary
The expansion of dengue vectors from lowland plains to the upland hilly regions of Nepal suggests the likelihood of increased risk of dengue. Our objective was to assess the effects of meteorological variables on vector indices and populations of dengue vectors in two different ecological regions of Nepal. The effect of meteorological variables on vector indices (house index, container index and Breteau index) and Aedes spp. population abundance was analyzed. Dengue was first reported in Nepal in 2004 from Chitwan District, while the first outbreak occurred in 2006 with confirmed cases from nine districts of the lowland region, known as Terai in Nepal [5, 6]. The major outbreak occurred in 2010 with 917 cases including five deaths that affected 12 districts of central and western Nepal [7]. The periodic outbreaks together with the expansion of dengue affected districts suggest a perpetual threat of dengue in the country
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