First detection of voltage-gated sodium channel mutations in collected from Bangladesh.

Background & Objectives: Phlebotomus argentipes is the main vector of visceral leishmaniasis in Bangladesh and is controlled using deltamethrin, a synthetic pyrethroid, through indoor residual spraying (IRS). A mutation at L1014 (leucine at codon 1014) of the voltage-gated sodium channel (VGSC), known as a knockdown resistance (kdr) gene, is thought to be an important pyrethroid resistance mechanism. This study detected mutations at codon 1014, and at codons 1011, 1016, and 1020, which are kdr sites in other insects. The kdr relationship with deltamethrin resistance in P. argentipes from an IRS-targeted site in Bangladesh was also evaluated.

Methods: Sand flies were collected from Magurjora village, Mymensingh district, Bangladesh in November 2012. A WHO cone bioassay test using deltamethrin was conducted and specimens were grouped as 'live' or 'dead'. After morphological identification, genomic DNA was used to genotype a partial VGSC gene from P. argentipes. The kdr/ pyrethroid resistance relationship was evaluated using Fisher's exact test.

Results: Targeted codons were genotyped from 8 'live' and 63 'dead' P. argentipes. All 'live' specimens had mutant alleles (L1014F and L1014S) at codon 1014. The mutant allele rate was 94% for 'live' specimens and 55% for 'dead' specimens. The mutant allele survival odds were higher for the wild-type L1014L allele, and L1014F odds were lower for L1014S. There were no mutations at codons 1011, 1016, and 1020.

Interpretation & Conclusion: The L1014 mutations suggested that pyrethroid resistance had appeared in Bangladesh. Further research on kdr mutations in P. argentipes is important for the appropriate IRS.