Aedes aegypti is a vector for a variety of arboviral infectious diseases including dengue, chikungunya, zika, and yellow fever. Dengue is the most prevalent among them; the number of dengue cases has increased thirty-fold in the past 50 years. Control of this important vector highly relies on the use of insecticides, especially pyrethroids. Development of pyrethroid resistance, however, is a major obstacle to mosquito/disease control worldwide. We studied the relationships between alleles in the target site of pyrethroid insecticides, voltage-sensitive sodium channel (Vssc), and pyrethroid resistance of Ae. aegypti. We found that a high frequency (&gt;78%) of Ae. aegypti collected from Vietnam and Cambodia had the L982W allele in the Vssc. L982W mutation is located in the highly conserved region of Vssc that is associated with sodium-ion selectivity and permeation rate. Newly established strains having the L982W allele exhibited similar or even higher levels of resistance to pyrethroids than those having V1016G, a typical knockdown resistance allele in Asia. Furthermore, concomitant mutations L982W+F1534C and S989P+V1016G+F1534C were confirmed, and strains having these multiple mutations exhibited incomparably higher levels of resistance to permethrin and deltamethrin than any other field population ever reported. Molecular modeling analysis was also conducted and we confirmed that these concomitant mutant alleles could interfere with approaching pyrethroid to Vssc. Remarkably, &gt;90% of Vssc of Ae. aegypti were occupied by these hyperresistant haplotypes in Phnom Penh city, Cambodia. Analysis of whole Vssc coding genes suggested that these strong Vssc haplotypes were generated through gene recombination events. So far, L982W has never been detected in Vssc of Ae. aegypti from any other neighboring countries including China, Lao, Myanmar, and Thailand. We strongly emphasize the importance strengthening the monitoring of these mutant alleles, especially in South East Asia to take appropriate countermeasures before they spread globally through Indochina Peninsula.

Hyper pyrethroid-resistant dengue vectors in Indochina Peninsula: threats of concomitant knockdown resistance mutations

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