Knockdown resistance (kdr) in dengue vectors, Aedes aegypti and Aedes albopictus: A post-flood risk assessment
Even though dengue remains a major threat in Malaysia, information on insecticide resistance of vectors, along with the underlying genetic basis of such resistance, and the impact of a natural flooding disaster remains sparse. Kelantan was one of the states of Malaysia severely affected by monsoon flooding in December 2014. We examined the resistance profile of Aedes mosquitoes in after the big flood, comparing the susceptibility of Ae. aegypti and Ae. albopictus from flooded and unflooded areas. We also sought to validate a simple molecular assay for detecting knockdown resistance (kdr) mutations in the voltage-gated sodium channel (VGSC) gene of the mosquitoes. Mosquito immatures were collected by using ovitraps in Kampung Baru, Pasir Pekan, Tumpat (flooded area), and Bandar Baru Kubang Kerian, Kubang Kerian (unflooded area) five months after the flood disaster. The samples were reared to adult mosquitoes and bio-assayed following World Health Organization (WHO) protocol against deltamethrin (0.05%) and pirimiphos-methyl (0.25%) to evaluate their susceptibility. The DNA molecular assays focused on amino acid substitution in domain II (S989, I1011, L1014, and V1016) and domain III (F1534C) in segment 6 of the VGSC gene. Aedes aegypti and Ae. albopictus from both locations were found to be susceptible to pirimiphos-methyl (mortality >98%). A high level of resistance to deltamethrin was detected in Ae. Aegypti; the unflooded area mosquitoes had significantly lower mortality (17%) than the flooded area (74%). Investigation of kdr mutation showed F1534C substitution in the VGSC gene of Ae. aegypti from the flooded and unflooded areas, with an insignificant difference in frequency of 83 and 75% (P > 0.05). This mutation was not detected in Ae. albopictus.