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

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>The chemical control of the mosquito<jats:italic>Aedes aegypti</jats:italic>, 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<jats:sub>V</jats:sub>), commonly known as<jats:italic>kdr</jats:italic>mutations, confer the mosquito with knockdown resistance. Our aim was to evaluate the allelic composition of natural populations of Brazilian<jats:italic>Ae. aegypti</jats:italic>at both<jats:italic>kdr</jats:italic>sites.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>The AaNa<jats:sub>V</jats:sub>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.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>The 350 bp sequence spanning the IIIS6 region of the<jats:italic>AaNa</jats:italic><jats:sub><jats:italic>V</jats:italic></jats:sub>gene revealed the occurrence of the<jats:italic>kdr</jats:italic>mutation Phe1534Cys in Brazil. Concerning the individual genotyping, beyond the susceptible wild-type (Na<jats:sub>V</jats:sub><jats:sup>S</jats:sup>), two<jats:italic>kdr</jats:italic>alleles were identified: substitutions restricted to the 1534 position (Na<jats:sub>V</jats:sub><jats:sup>R1</jats:sup>) or simultaneous substitutions in both 1016 and 1534 sites (Na<jats:sub>V</jats:sub><jats:sup>R2</jats:sup>). A clear regional distribution pattern of these alleles was observed. The Na<jats:sub>V</jats:sub><jats:sup>R1</jats:sup><jats:italic>kdr</jats:italic>allele occurred in all localities, while Na<jats:sub>V</jats:sub><jats:sup>R2</jats:sup>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<jats:italic>kdr</jats:italic>mutations, mainly the double mutant allele Na<jats:sub>V</jats:sub><jats:sup>R2</jats:sup>. Recent samples also indicate that Na<jats:sub>V</jats:sub><jats:sup>R2</jats:sup>is spreading towards the Northern region.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>We have found that in addition to the previously reported Val1016Ile<jats:italic>kdr</jats:italic>mutation, the Phe1534Cys mutation also occurs in Brazil. Allelic composition at both sites was important to elucidate the actual distribution of<jats:italic>kdr</jats:italic>mutations throughout the country. Studies to determine gene flow and the fitness costs of these<jats:italic>kdr</jats:italic>alleles are underway and will be important to better understand the dynamics of<jats:italic>Ae. aegypti</jats:italic>pyrethroid resistance.</jats:p></jats:sec>