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Aedes (Stegomyia) aegypti (Diptera, Culicidae) da ilha da Madeira: origem geográfica e resistência aos insecticidas
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Aedes (Stegomyia) aegypti (Linnaeus, 1762) é o principal vector da febre amarela e da dengue assim como um agente de incomodidade. Esta espécie invasora está actualmente presente na ilha da Madeira (Portugal). Foi detectada pela primeira vez em Outubro de 2005, mas a origem geográfica da população de mosquitos é desconhecida. Apesar das medidas de controlo vectorial implementadas na região, Ae. aegypti continua a expandir-se. Isto pode ser devido à presença de resistência aos insecticidas aplicados no controlo vectorial desta espécie. Assim, os objectivos deste estudo foram: (i) avaliar o nível de sensibilidade da população de Ae. aegypti aos insecticidas; (ii) caracterizar possíveis mecanismos de resistência envolvidos e; (iii) estabelecer a sua origem geográfica através do uso de marcadores de ADN mitocondrial (COI e ND4).
De acordo com os resultados dos bioensaios da OMS, Ae. aegypti da ilha da Madeira apresenta alta susceptibilidade ao malatião, com taxas de mortalidade das fêmeas expostas de 99.0%. No entanto, a população mostrou um alto nível de resistência ao DDT e permetrina, com valores de mortalidade de 29.4% e 33.3%, respectivamente. Observou-se também uma marcada resistência à deltametrina, com uma taxa de mortalidade de 65.2%. Os ensaios de garrafa do CDC com alfa-cipermetrina e ciflutrina mostraram uma alta susceptibilidade de Ae. aegypti a estes insecticidas, com taxas de mortalidade de 100%.
A sequenciação do gene do canal de sódio de Ae. aegypti, local alvo dos piretróides e DDT, revelou a presença de apenas uma mutação associada à resistência, V1016I (mutação kdr). A baixa frequência alélica (6%) desta mutação sugere que outros mecanismos podem estar presentes na resistência a estes insecticidas.
Ambos os genes COI e ND4 apresentaram níveis baixos de variabilidade genética consistente com a recente introdução de Ae. aegypti na ilha. Observou-se dois haplótipos mitocondriais. A rede de haplótipos de ambos os genes sugere dois cenários para o estabelecimento de Ae. aegypti na região: i) ocorreram pelo menos duas introduções independentes correspondendo a cada haplótipo; ii) o estabelecimento de ambos os haplótipos ocorreu simultaneamente, no mesmo evento de colonização. Baseado na distribuição geográfica dos haplótipos e da mutação kdr observada na ilha, assim como a população humana migrante da Madeira, o Brasil e a Venezuela são os locais mais prováveis de origem da população de Ae. aegypti local.
A frequência dos alelos kdr e análise filogeográfica suportam a hipótese de que a resistência a insecticidas detectada na população da ilha da Madeira já existia na população de Ae. aegypti que colonizou a região.
Aedes (Stegomyia) aegypti (Linnaeus, 1762) is the primary vector of urban yellow fever and dengue viruses as well as a nuisance agent. This invasive species is currently present in Madeira Island (Portugal). It was first detected in October 2005 but the geographic origin of this mosquito population is unknown. Despite the vector control measures implemented in the region, Ae. aegypti, seems to be spreading. This may be due to the presence of resistance to insecticides. The aims of this study were: (i) to measure the susceptibility level of Ae. aegypti population to insecticides; (ii) to characterize possible resistance mechanisms involved and; (iii) to establish the geographical origin of Ae. aegypti present in Madeira Island through the use of mitochondrial DNA markers (COI and ND4).. According to WHO bioassay results, Ae. aegypti from Madeira island presents high susceptibility to malathion, with mortality rates of exposed females of 99.0%. However, the population showed a high resistance level to DDT and permethrin, with mortality values of 29.4% and 33.3%, respectively. There was also a marked resistance to deltamethrin, with a mortality rate of 65.2%. The CDC bottle assays with alpha-cypermethrin and cyfluthrin showed a high susceptibility of Ae. aegypti to these insecticides, with mortality rates of 100%. Sequencing of the DDT/pyrethoid insecticide target site at the voltage-gated sodium channel gene of Ae. aegypti identified the presence of only one resistance-associated mutation, V1016I (kdr-mutation). This mutation showed a reduced allele frequency (6%), which suggests the presence of other insecticide resistance mechanisms rather than kdr. Both COI and ND4 presented low levels of nucleotidic variability, consistent with a recent introduction of Ae. aegypti in the island. Two mitochondrial haplotypes were found. The haplotype network of the COI and ND4 genes suggest two scenarios for the establishment of Ae. aegypti in the region: i) two independent introductions corresponding to each haplotype; ii) the establishment of both haplotypes simultaneously at the same colonization event. Based on the geographic distribution of the haplotypes and the kdr-mutation detected in the island, and the origin of the migrant human population of Madeira, Brazil and Venezuela are the most likely source-places of the local Ae. aegypti. The frequency of the kdr alleles and the phylogeographic analysis support the assumption that the resistance to insecticides detected in the population of Madeira Island already exist in the individuals that colonized the region.
Aedes (Stegomyia) aegypti (Linnaeus, 1762) is the primary vector of urban yellow fever and dengue viruses as well as a nuisance agent. This invasive species is currently present in Madeira Island (Portugal). It was first detected in October 2005 but the geographic origin of this mosquito population is unknown. Despite the vector control measures implemented in the region, Ae. aegypti, seems to be spreading. This may be due to the presence of resistance to insecticides. The aims of this study were: (i) to measure the susceptibility level of Ae. aegypti population to insecticides; (ii) to characterize possible resistance mechanisms involved and; (iii) to establish the geographical origin of Ae. aegypti present in Madeira Island through the use of mitochondrial DNA markers (COI and ND4).. According to WHO bioassay results, Ae. aegypti from Madeira island presents high susceptibility to malathion, with mortality rates of exposed females of 99.0%. However, the population showed a high resistance level to DDT and permethrin, with mortality values of 29.4% and 33.3%, respectively. There was also a marked resistance to deltamethrin, with a mortality rate of 65.2%. The CDC bottle assays with alpha-cypermethrin and cyfluthrin showed a high susceptibility of Ae. aegypti to these insecticides, with mortality rates of 100%. Sequencing of the DDT/pyrethoid insecticide target site at the voltage-gated sodium channel gene of Ae. aegypti identified the presence of only one resistance-associated mutation, V1016I (kdr-mutation). This mutation showed a reduced allele frequency (6%), which suggests the presence of other insecticide resistance mechanisms rather than kdr. Both COI and ND4 presented low levels of nucleotidic variability, consistent with a recent introduction of Ae. aegypti in the island. Two mitochondrial haplotypes were found. The haplotype network of the COI and ND4 genes suggest two scenarios for the establishment of Ae. aegypti in the region: i) two independent introductions corresponding to each haplotype; ii) the establishment of both haplotypes simultaneously at the same colonization event. Based on the geographic distribution of the haplotypes and the kdr-mutation detected in the island, and the origin of the migrant human population of Madeira, Brazil and Venezuela are the most likely source-places of the local Ae. aegypti. The frequency of the kdr alleles and the phylogeographic analysis support the assumption that the resistance to insecticides detected in the population of Madeira Island already exist in the individuals that colonized the region.
Descrição
Palavras-chave
Aedes aegypti Resistência a insecticidas Marcadores mitocondriais Origem geográfica Parasitologia médica Vectores Marcadores mitocondriais Madeira
Contexto Educativo
Citação
Editora
Instituto de Higiene e Medicina Tropical