Resistance Profile Confirming the Presence of Three Knock-Down Mutations: <i>S</i>989<i>P</i>, <i>V</i>1016<i>G</i> and <i>F</i>1534<i>C</i> in <i>Aedes aegypti</i> in the Arrondissements of Abomey-Calavi and Ouedo in Benin

Abstract

Context: The control of arboviruses such as Dengue focuses on the control of Aedes mosquitoes through the use of insecticides. Unfortunately, the effectiveness of this chemical control is influenced by the increasing frequency of insecticide resistance. The aim of this study was to assess the sensitivity of Aedes aegypti in the Abomey-Calavi district to pyrethroids, the frequency of kdr mutations and the level of expression of detoxification enzymes. Methodology: Aedes eggs were collected using 100 ovitraps in 04 districts of the Abomey-Calavi arrondissement and 96 ovitraps in Ouèdo. Female Aedes obtained were exposed to a diagnostic dose of permethrin, deltamethrin, alpha-cypermethrin and cyfluthrin according to the WHO tube test protocol. PCR was used to detect kdr mutations (F1534C, S989P, V1016G) in the voltage-gated sodium channel gene in exposed Aedes females. Finally, 65 females from the Abomey-Calavi district who had not been in contact with an insecticide were analyzed individually to assess the expression of detoxification enzymes. Results: The traps were highly positive, with a positivity rate of 77% in Abomey-Calavi and 85% in Ouèdo. The hatching and emergence rates were 89% and 50% respectively in Abomey-Calavi, and 46% and 43% in Ouèdo. Identification of these adults yielded Aedes aegypti with a total of 1857 (99.73%), compared with 5 (less than 1% of the total) for Aedes albopictus. Sensitivity tests showed resistance to deltamethrin (86.53% in Zoundja and 88.95% in Zoca) and permethrin (45% Tokpa-Zoungo). In Ouèdo, on the other hand, the mortality rate of Aedes after exposure to permethrin, deltamethrin, alpha-cypermethrin and cyfluthrin was 100%. PCR genotyping of female Aedes DNA revealed the presence of kdr mutation alleles at very high frequencies. The Aedes mosquitoes analyzed had significantly higher median levels of oxidase and glutathione s-transferase (GST) expression than the insecticide-sensitive Rockefeller reference strain. Conclusion: The detection of deltamethrin resistance, several kdr mutations and overexpression of glutathione s-transferases and oxidases underscores the urgency of implementing alternative control strategies against Aedes mosquitoes. In addition, the implementation of a systematic monitoring of insecticide resistance in Aedes in Benin will enable a better understanding of susceptibility trends in space and time, and thus the development of better alternative control strategies to better control this vector.