Abstract
BackgroundWhen the first systematic list of mosquitoes in Nepal was reported in 1990, there was no description of Aedes aegypti (L.), while Aedes albopictus (Skuse) has been included in the Stegomyia subgroup since the 1950s. The first record of Ae. aegypti in Nepal was reported in 2009, suggesting some coincidence between the invasion of this species and the first record of dengue fever in Nepal in 2006.ResultsWe performed a field survey of the distribution and insecticide susceptibility of Ae. aegypti and Ae. albopictus in Nepal in 2017 and 2018. Mosquito larvae were collected from used tires located along the streets of Kathmandu, Bharatpur and Pokhara, and a simplified bioassay was used to assess the susceptibility of the larvae to pyrethroid insecticides using d-allethrin. The presence or absence of point mutations in the voltage-gated sodium channel was also detected by direct sequencing. V1016G was detected at a high frequency and a strong correlation was observed between the frequencies of V1016G and susceptibility indices in Ae. aegypti populations. F1534C was also detected at a relatively low frequency. In Ae. albopictus populations, susceptibilities to d-allethrin were high and no point mutations were detected. Analysis of the cytochrome c oxidase subunit 1 (cox1) gene was performed for assessing genetic diversity and the existence of two strains were identified in Ae. aegypti populations. One consisted of 9 globally-distributed haplotypes while the other was derived from an African haplotype.ConclusionsThe high pyrethroid resistance, high V1016G frequency, and relatively low quantity of insecticides used to control dengue vectors in Nepal may have resulted in only weak selection pressure favoring insecticide resistance and could support the hypothesis that this species has recently been introduced from neighboring Asian countries where pyrethroid resistance is relatively widespread.
Highlights
When the first systematic list of mosquitoes in Nepal was reported in 1990, there was no description of Aedes aegypti (L.), while Aedes albopictus (Skuse) has been included in the Stegomyia subgroup since the 1950s
Pyrethroid susceptibility and point mutations in the voltage‐gated sodium channel in Ae. aegypti and Ae. albopictus Figure 1 shows the species distribution patterns of both Ae. aegypti and Ae. albopictus larvae collected from used tires in three cities in Nepal
High pyrethroid resistance presumably caused by the high V1016G frequency in Ae. aegypti in Nepal was, to the best of our knowledge, found for the first time in the present study
Summary
When the first systematic list of mosquitoes in Nepal was reported in 1990, there was no description of Aedes aegypti (L.), while Aedes albopictus (Skuse) has been included in the Stegomyia subgroup since the 1950s. The highest number of dengue cases (7151) was reported in Bagmati Province including the capital city (Kathmandu) in which 1583 cases have been confirmed. This could influence the national campaign of “Visit Nepal Year 2020” which targeted two million foreign tourists [9]. Fogging of insecticides (deltamethrin) has been carried out in urban area for controlling vector mosquitoes (Ae. aegypti and Ae. albopictus) (GR, unpublished data)
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