Evaluation of insecticide resistance in Aedes aegypti populations connected by roads and rivers: the case of Tocantins state in Brazil

BACKGROUND The longstanding application of insecticides for vector control without periodic monitoring of the population response to these chemicals can directly drive the selection of resistant populations of vector mosquitoes. Tocantins is the newest state of the Brazilian Federation. Despite a historically high number of dengue cases, studies and monitoring data concerning insecticide resistance in the state are lacking. OBJECTIVES To verify the resistance status of Aedes aegypti from 10 populations distributed throughout the state connected by rivers and roads. METHODS Between 50 and 150 ovitraps were installed in house gardens within each municipality. Collection points were established based on the importance of the towns and on geographic aspects. Dose response bioassays were performed in accordance with World Health Organization guidelines. Molecular assays were conducted to detect kdr mutations, which are related to pyrethroid resistance. FINDINGS Of the 3,200 ovitrap paddles analysed, 25.8% contained eggs, with a total of 55,687 eggs collected. With the exception of Caseara, all evaluated populations were considered to be resistant to temephos. The data showed different levels of resistance to deltamethrin among the samples. Caseara and Guaraí showed the lowest RR95 values. On average, the NaVR1 kdr allele was most frequent (40.3%), followed by NaVS (38.1%), and NaVR2 (21.6%). Palmas, the capital of the state, had the highest frequency of kdr alleles (87.5%). MAIN CONCLUSIONS With the exception of Palmas, the towns with the highest indexes (ovitrap positivity, number and density of eggs), as well with high levels of resistance and kdr alleles were located along the BR-153 road, indicating that the flow of people and cargo can contribute to the dispersion of the vector and potentially resistance. This study contributes substantially to knowledge regarding the insecticide resistance profile of Tocantins mosquito populations; the data generated via the study could facilitate the judicious use of insecticides by vector control programs.

Resistance to temephos and deltamethrin in Aedes aegypti from Brazil between 1985 and 2017

BACKGROUND Aedes aegypti populations in Brazil have been subjected to insecticide selection pressures with variable levels and sources since 1967. Therefore, the Brazilian Ministry of Health (MoH) coordinated the activities of an Ae. aegypti insecticide resistance monitoring network (MoReNAa) from 1999 to 2012. OBJECTIVES The objective of this study was to consolidate all information available from between 1985 and 2017 regarding the resistance status and mechanisms of Brazilian Ae. aegypti populations against the main insecticide compounds used at the national level, including the larvicide temephos (an organophosphate) and the adulticide deltamethrin (a pyrethroid). METHODS Data were gathered from two sources: a bibliographic review of studies published from 1985 to 2017, and unpublished data produced by our team within the MoReNAa between 1998 and 2012. A total of 146 municipalities were included, many of which were evaluated several times, totalling 457 evaluations for temephos and 274 for deltamethrin. Insecticide resistance data from the five Brazilian regions were examined separately using annual records of both the MoH supply of insecticides to each state and the dengue incidence in each evaluated municipality. FINDINGS Ae. aegypti resistance to temephos and deltamethrin, the main larvicide and adulticide, respectively, employed against mosquitoes in Brazil for a long time, was found to be widespread in the country, although with some regional variations. Comparisons between metabolic and target-site resistance mechanisms showed that one or another of these was the main component of pesticide resistance in each studied population. MAIN CONCLUSIONS (i) A robust dataset on the assessments of the insecticide resistance of Brazilian Ae. aegypti populations performed since 1985 was made available through our study. (ii) Our findings call into question the efficacy of chemical control as the sole methodology of vector control. (iii) It is necessary to ensure that sustainable insecticide resistance monitoring is maintained as a key component of integrated vector management. (iv) Consideration of additional parameters, beyond the supply of insecticides distributed by the MoH or the diverse local dynamics of dengue incidence, is necessary to find consistent correlations with heterogeneous vector resistance profiles.

Avaliação quantitativa do monitoramento da resistência a inseticidas em populações brasileiras de Aedes aegypti: uma análise temporal da dinâmica da resistência / Quantitative assessment of insecticide resistance monitoring in Brazilian populations of Aedes aegypti: a temporal analysis of resistance dynamics

Aedes aegypti é o vetor de uma série de arboviroses que atualmente circulam pelo Brasil, como dengue, Zika e chikungunya. Na ausência de vacinas ou de medicamentos específicos, a redução da densidade das populações de A. aegypti é a principal ferramenta de controle destes agravos. Ainda hoje, o controle químico é bastante confundido com o controle do vetor, ou seja, inseticidas continuam sendo amplamente aplicados em saúde pública. No Brasil, os organofosforados (OP) têm sido usados contra A. aegypti por anos, desde 1967, e os piretroides (PY) desde 2000. Os compostos mais amplamente utilizados em âmbito nacional têm sido o larvicida temephos (OP) e o adulticida deltametrina (PY). Em 2009, os Reguladores do Desenvolvimento de Insetos (IGR) e o OP malathion foram introduzidos para utilização, respectivamente, no controle de larvas e de adultos. O uso intenso de inseticidas pode selecionar indivíduos resistentes nas populações naturais do vetor, eliminando os espécimes suscetíveis e reduzindo a variabilidade das populações. No presente estudo, apresentamos: (1) uma revisão sistemática, baseada na bibliografia disponível até julho de 2017 e em dados inéditos de nossa equipe, do status da resistência a temephos e deltametrina de populações brasileiras de A. aegypti; estes dados foram avaliados por Região e comparados com a incidência de dengue por município e com o fornecimento de inseticidades aos estados; (2) o perfil de suscetibilidade de 12 populações do vetor frente ao IGR diflubenzuron, um inibidor de síntese de quitina, após sua introdução no país e (3) o uso de ferramentas matemáticas para procurar correlações entre resistência a inseticidas com os mecanismos avaliados e potencialmente, com a incidência de dengue

Ensaios dose-resposta detectaram altos níveis de resistência para o temephos e para deltametrina embora todas as amostras avaliadas tenham sido suscetíveis ao diflubenzuron. Diferentes padrões regionais de incidência de dengue foram identificados e sua correlação com a resistência a inseticidas foi variável. Os dados também permitiram comparar duas metodologias qualitativas de avaliação da resistência de adultos a inseticidas, 'CDC' (garrafas impregnadas) e 'WHO' (papéis impregnados), sugerindo que a primeira tende a induzir maiores taxas de mortalidade. A resistência metabólica sempre foi maior em fêmeas adultas do que em larvas; glutationa-S-transferases e esterases foram as principais classes enzimáticas alteradas. Em algumas populações do vetor, no caso de resistência a PY, foi possível identificar a opção por resistência metabólica ou, alternativamente, por alteração do sitio-alvo. Regressão de Poisson identificou relação significativa entre resistência e taxas de incidência de dengue, sugerindo impacto da intensificação do controle químico nos perfis de populações do vetor. Regressão logística detectou associação entre o sitio alvo de PY, o Nav, e resistência a deltametrina; foram ainda detectadas alterações de classes específicas de enzimas detoxificantes e resistência a deltametrina, mas não a temephos. Para compreender o perfil da contribuição das diferentes variáveis disponíveis sobre a resistência, iniciamos a decomposição de dados por análise de Componentes Principais (PCA). O histórico do status da resistência a temephos e deltametrina em populações brasileiras de A. aegypti revelou a disseminação da resistência aos principais inseticidas utilizados pelo Programa Nacional de Controle da Dengue, mostrando o caráter multifatorial da resistência no país. (AU)

The efficacy of a chitin synthesis inhibitor against field populations of organophosphate-resistant Aedes aegypti in Brazil

The mosquito Aedes aegypti is the main focus of dengue control campaigns. Because of widespread resistance against conventional chemical insecticides, chitin synthesis inhibitors (CSIs) are considered control alternatives. We evaluated the resistance status of four Brazilian Ae. aegypti populations to both the organophosphate temephos and the pyrethroid deltamethrin, which are used in Brazil to control larvae and adults, respectively. All vector populations exhibited high levels of temephos resistance and varying rates of alterations in their susceptibility to pyrethroids. The effect of the CSI novaluron on these populations was also investigated. Novaluron was effective against all populations under laboratory conditions. Field-simulated assays with partial water replacement were conducted to evaluate novaluron persistence. Bioassays were continued until an adult emergence inhibition of at least 70% was attained. We found a residual effect of eight weeks under indoor conditions and novaluron persisted for five-six weeks in assays conducted in an external area. Our data show that novaluron is effective against the Ae. aegypti populations tested, regardless of their resistance to conventional chemical insecticides.