Discussion

Pyrethroids are regularly used as a control measure for dengue fever in Saudi Arabia. Effectiveness of control may be impacted by resistance but there is lacking information on insecticide resistance in Ae. aegypti in the Middle Eastern Region. Aedes aegypti from the two primary dengue-endemic areas of Saudi Arabia (Makkah and Jeddah) were assayed for resistance phenotypes; their target site mutations investigated using sequencing and genotyping; and metabolic resistance mechanisms investigated using microarrays technology. Both strains were resistant to multiple insecticides, with especially high deltamethrin resistance in Makkah. Three kdr mutations were detected (F1534C, V1016G, S989P), two of which were previously only identified in Asia. The V1016 and S989P mutations were in perfect linkage disequilibrium (LD) and strongly predicted deltamethrin resistance. Microarray analysis was used to identify genes differentially expressed between two susceptible strains and Saudi Arabian strains from Makkah and Jeddah. Results showed enrichment of P450s, some previously identified as pyrethroid metabolisers. However, the lead candidate gene statistically, CYP9J7 has not previously been functionally-investigated and we investigated its metabolic capacity via in vitro insecticide metabolizm assays. No depletion of permethrin and was noted. Surprisingly, CYP9J7 metabolized the organophosphate malathion. Mosquitoes from Makkah and Jeddah are highly resistant to pyrethroids. The gene expression and target site mutation data propose that the Jeddah strain relies on both metabolic and target site resistance mechanisms, with evidence suggesting the latter may be more prominent at present. Further work is needed to identify whether the organophosphate metabolism detected represents detoxification or activation, which have opposing implications for resistance management.