Distribution and dissemination of the Val1016Ile and Phe1534Cys Kdr mutations in Aedes aegypti Brazilian natural populations

Abstract

Background

The chemical control of the mosquito Aedes aegypti, the major vector of dengue, is being seriously threatened due to the development of pyrethroid resistance. Substitutions in the 1016 and 1534 sites of the voltage gated sodium channel (AaNa _V), commonly known as kdr mutations, confer the mosquito with knockdown resistance. Our aim was to evaluate the allelic composition of natural populations of Brazilian Ae. aegypti at both kdr sites.

Methods

The AaNa _V IIIS6 region was cloned and sequenced from three Brazilian populations. Additionally, individual mosquitoes from 30 populations throughout the country were genotyped for 1016 and 1534 sites, based in allele-specific PCR. For individual genotypes both sites were considered as a single locus.

Results

The 350 bp sequence spanning the IIIS6 region of the AaNa _V gene revealed the occurrence of the kdr mutation Phe1534Cys in Brazil. Concerning the individual genotyping, beyond the susceptible wild-type (Na _V ^S), two kdr alleles were identified: substitutions restricted to the 1534 position (Na _V ^R1) or simultaneous substitutions in both 1016 and 1534 sites (Na _V ^R2). A clear regional distribution pattern of these alleles was observed. The Na _V ^R1 kdr allele occurred in all localities, while Na _V ^R2 was more frequent in the Central and Southeastern localities. Locations that were sampled multiple times in the course of a decade revealed an increase in frequency of the kdr mutations, mainly the double mutant allele Na _V ^R2. Recent samples also indicate that Na _V ^R2 is spreading towards the Northern region.

Conclusions

We have found that in addition to the previously reported Val1016Ile kdr mutation, the Phe1534Cys mutation also occurs in Brazil. Allelic composition at both sites was important to elucidate the actual distribution of kdr mutations throughout the country. Studies to determine gene flow and the fitness costs of these kdr alleles are underway and will be important to better understand the dynamics of Ae. aegypti pyrethroid resistance.