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Background   Several mutations in voltage gated sodium channel (Na V ) have been identified in  Aedes aegypti  populations worldwide. However, only few are related to knockdown resistance to pyrethroids, most of which with variations in the 1016 and 1534 Na V  sites. In Brazil, at least two  Na   V   alleles are known: Na V R1, with a substitution in the 1534 (1016 Val +  + 1534 Ile  kdr  ) and Na V R2, with substitutions in both 1016 and sites (1016Ile kdr  + 1534Cys  kdr  ). There is also the duplication in the  Na   V   gene, with one copy carrying the substitution Ile1011Met, although its effects on pyrethroid resistance remain to be clarified. Our goals in this study were (1) to determine the role of each  kdr  Na V  allele and the duplication on pyrethroid resistance and (2) to screen the frequency of the  kdr  alleles in 27 several natural  Ae. aegypti  populations from the metropolitan region of Rio de Janeiro.Methods   Pyrethroid resistance was evaluated by a knockdown time ( Kd T) assay, an adaptation of the WHO test tubes with paper impregnated with deltamethrin. We used laboratory-selected  Ae. aegypti  lineages: R1R1 and R2R2 (homozygous for the  kdr  Na V R1 and Na V R2 alleles, respectively), Dup (with duplication in the  Na   V   gene), Rockefeller (the susceptibility reference control), and F1 hybrids among them. Genotyping of both 1016 and 1534 Na V  sites was performed in 811  Ae. aegypti  sampled from 27 localities from Rio de Janeiro (17), Niterói (6) and Nova Iguaçu (4) cities, Rio de Janeiro State, Brazil, with a TaqMan real time PCR approach.Results   The laboratory lineages R1R1, R2R2, and R1R2 were the only ones that needed more than 60 minutes to  knock down  all the insects exposed to the pyrethroid, being the  Kd T R2R2 > R1R2 > R1R1, corroborating the recessive nature of the  kdr  mutations. Frequency of  kdr  alleles Na V R1 and Na V R2 in field-caught mosquitoes varied from 0 to 52% and 43 to 86%, respectively, evidencing high levels of “resistant genotypes” (R1R1, R1R2, and R2R2), which together summed 60 to 100% in  Ae. aegypti  populations from Rio de Janeiro.Conclusions   The Na V R1 and Na V R2  kdr  alleles confer resistance to the pyrethroid deltamethrin in homozygotes and R1R2 heterozygotes, being the R2R2 most resistant genotype. The allele containing duplication in the Na V  gene, with a mutation in the 1011 site, did not confer resistance under the tested conditions. The frequencies of the “resistant genotypes” are elevated in  Ae. aegypti  natural populations from Rio de Janeiro.

biomed research international

Levels of Resistance to Pyrethroid among DistinctkdrAlleles inAedes aegyptiLaboratory Lines and Frequency ofkdrAlleles in 27 Natural Populations from Rio de Janeiro, Brazil