Mecanismos de resistencia y perfil de expresion de genes involucrados en la resistencia a la deltametrina en poblaciones de Aedes aegypti (L.) (Diptera: Culicidae) en México

La exposición prolongada a insecticidas, presiona y selecciona poblaciones de mosquitos altamente resistentes. En este estudio se determinaron los parámetros de susceptibilidad a deltametrina CK50 y CL50 en seis poblaciones de Aedes aegypti a través de cinco generaciones de selección, así mismo, se determinó la heredabilidad de la resitencia a deltametrina (h2) con el conjunto de parámetros obtenidos (CK50 y CL50). La frecuencia de las mutaciones kdr V410L, V1016I y F1534C y los niveles de actividad de tres familias de enzimas (esterasas [α y β], oxidasas de función mixta y glutatión S-transferasas) relacionadas con la desintoxicación a insecticidas fueron determinados en cada generación. Finalmente comparamos los niveles de expresión de genes que confieren resistencia. Nuestros resultados señalan un incremnento en los valores de CK50 y CL50 despues de la selección con deltametrina (FS5 vs FS0). De acuerdo con los factores de resistencia (FR), obtuvimos incrementos de 1.5 a 5.6 veces para CL50 y 1.3-3.8 veces para CK50. Los individuos triple homocigoto resistentes (tri-locus, LL / II / CC) estuvieron presentes en la generación parental y aumentaron en frecuencia después de la selección con deltamertina. La frecuencia de L410 aumentó de 1.18 a 2.63, I1016 se entre 1.19 y 2.79 veces, y C1534 se fijó en todas las cepas después de la selección con deltametrina. La actividad enzimática varió significativamente durante las generaciones de selección. Sin embargo, α y β esterasas permanecieron alteradas en algunas poblaciones y solamente dos mostraron un incremento en los niveles medios de actividad de GST después de la selección con deltametrina. Los genes diferencialmente expresados fueron agrupados en 12 categorías. Los genes de cutícula (CUT) fueron los más sobreexpresados después de la selección con deltametrina. Los elevados parámetros de susceptibilidad y su asociación con altas frecuencias de mutaciones kdr (V410L, V1016I y F1534C), así como, la sobreexpresión de genes de cutícula (CUT) sugieren un papel importante en la resistencia a la deltametrina. Con base a estos resultados, destacamos la necesidad de implementar estrategias que involucren el monitoreo de frecuencias kdr y profundizar en el análisis de la morfología y composición cuticular en Aedes aegypti y asociación de estos genes en la resistencia cuticular a piretroides. Abstract Prolonged exposure to insecticides, press and select populations of mosquitoes highly resistant. In this study the parameters of susceptibility to deltamethrin KC50 and LC50 were determined in six natural populations of Aedes aegypti through five generations of selection, the set of parameters obtained (KC50 and LC50) was subjected to heritability analysis of resistance (h2). Likewise, the frequency of the kdr mutations V410L, V1016I, F1534C and the activity levels of three enzyme families (esterases [α and β], mixed function oxidases and glutathione S-transferases) related to insecticide detoxification were determined in each generation. Finally, we compare the expression levels of genes that confer resistance. Our results indicate an increase in the values of KC50 and LC50 after selection with deltamethrin (FS5 vs FS0). According to the resistance factors (FR), we obtained increments of 1.5 to 5.6 times for LC50 and 1.3-3.8 times for KC50. Triple homozygous resistant individuals (trilocus, LL/II / CC) were present in the parental generation and increased in frequency after selection with deltamertin. The frequency of L410 increased from 1.18 to 2.63 for V1016 an increase was observed between 1.19 and 2.79 times, and C1534 was fixed in all strains after deltamethrin selection. Enzymatic activity varied significantly during the generations of selection. However, only α and β esterases remained altered in some of the populations and only two populations showed an increase in the average levels of GST activity after selection with deltamethrin. Differentially expressed genes were grouped into 12 categories. The cuticle genes (CUT) were the most overexpressed after selection with deltamethrin. The high susceptibility parameters and their association with high frequencies of kdr mutations (V410L, V1016I and F1534C), as well as cuticle gene overexpression (CUT) suggest an important role in resistance to deltamethrin. Based on these results, we highlight the need to implement strategies that involve monitoring of kdr frequencies and deepen the analysis of the morphology and cuticular composition in Aedes aegypti and association of these genes in pyrethroid cuticular resistance

House screening with insecticide-treated netting provides sustained reductions in domestic populations of Aedes aegypti in Merida, Mexico.

There is a need for effective methods to control Aedes aegypti and prevent the transmission of dengue, chikungunya, yellow fever and Zika viruses. Insecticide treated screening (ITS) is a promising approach, particularly as it targets adult mosquitoes to reduce human-mosquito contact. A cluster-randomised controlled trial evaluated the entomological efficacy of ITS based intervention, which consisted of the installation of pyrethroid-impregnated long-lasting insecticide-treated netting material fixed as framed screens on external doors and windows. A total of 10 treatment and 10 control clusters (100 houses/cluster) were distributed throughout the city of Merida, Mexico. Cross-sectional entomological surveys quantified indoor adult mosquito infestation at baseline (pre-intervention) and throughout four post-intervention (PI) surveys spaced at 6-month intervals corresponding to dry/rainy seasons over two years (2012-2014). A total of 844 households from intervention clusters (86% coverage) were protected with ITS at the start of the trial. Significant reductions in the indoor presence and abundance of Ae. aegypti adults (OR = 0.48 and IRR = 0.45, P<0.05 respectively) and the indoor presence and abundance of Ae. aegypti female mosquitoes (OR = 0.47 and IRR = 0.44, P<0.05 respectively) were detected in intervention clusters compared to controls. This high level of protective effect was sustained for up to 24 months PI. Insecticidal activity of the ITS material declined with time, with ~70% mortality being demonstrated in susceptible mosquito cohorts up to 24 months after installation. The strong and sustained entomological impact observed in this study demonstrates the potential of house screening as a feasible, alternative approach to a sustained long-term impact on household infestations of Ae. aegypti. Larger trials quantifying the effectiveness of ITS on epidemiological endpoints are warranted and therefore recommended

Mosquito Excito-Repellency: Effects on Behavior and the Development of Insecticide Resistance

Mosquito’s resistance to avoiding insecticide-treated surfaces (“excito-repellency”) has two effects: irritation from direct contact with a treated area and repellency as an avoidance response to contact with treated surfaces. Nowadays, this behavior appears to reduce the success of mosquito control programs, particularly those based on insecticide-driven strategies. Different systems have been designed to assess the excito-repellency, evaluating numerous insecticides’ irritants, deterrents, and toxic properties at different concentrations. The information provides valuable insights regarding the patterns of mosquito behavior based on their physiological conditions, such as the age of the mosquitoes and the duration of the tests. However, the physiological processes resulting from chemical stimulus contact “chemoreception”) are still poorly explored and understood. This review provides an overview of insecticide effects on mosquito behavior and describes the mechanisms involved in chemical stimuli uptake, translation, and recognition

Community Engagement and Social Assessment for <em>Wolbachia</em>-Based Suppression of Natural Populations of <em>Aedes aegypti</em>: The Mexican Experience

The Wolbachia-based approach is under evaluation as a control strategy against Aedes aegypti in Mexico. From 2017 to 2019, we performed a pilot study to evaluate an open-field mass-release of wAlbB-infected Ae. aegypti male mosquitoes, as part of an integrated vector management (IVM) plan led by the Ministry of Health in Mexico to suppress natural populations of Ae. aegypti in southern Mexico. Community engagement and social evaluation were part of the key activities conducted. Overall, results showed the positive benefits of this Wolbachia-based method in the reduction of Aedes mosquitoes (90%). Mosquito’s nuisance at bedtime and the increasing circulation of mosquitoes during the releasing days were reported as the negative perceptions of this method. Importantly, participants understood the difference between wild mosquitoes and those released as part of the project, as well as the importance of the IVM. A significant number of the population accepted and supported the project, and feedback was given to improve future mosquito-releasing activities. The social license was a key factor in the success of the intervention and should be part of innovative paradigms for mosquito-vector control strategies involving community engagement. We outline the Mexican experience of community engagement and social assessment in implementing a Wolbachia-based strategy

Detección de Aedes (Stegomyia) albopictus (Skuse) en ovitrampas en Mérida, México

Introduction: The vector-borne diseases program in México has an established network of ovitraps for entomological surveillance of Aedes spp. In response to reports of Aedes albopictus in the periphery of Mérida, the state capital of Yucatán, the Ministry of Health increased the specificity of this surveillance.Objective: To describe the presence and distribution of Ae. albopictus in Mérida and its relative abundance compared to Aedes aegypti in ovitraps of the vector control program.Materials and methods: During October, 2019, 91 ovitraps were randomly selected from 31 neighborhoods of Mérida. Mosquitoes were reared at the insectary of the Collaborative Unit for Entomological Bioassays of the Autonomous University of Yucatán from eggs collected in the field. Relative abundance was determined for adult individuals of each identified species and neighborhood.Results: 32 % of the neighborhoods were positive for Ae. albopictus and 100 % for Ae. aegypti. A total of 28 adults of Ae. albopictus (10 females and 18 males) were obtained from ovitraps. No correlation was observed between the abundance of Ae. aegypti and Ae. albopictus for both adults and females (p&gt;0.05) at the neighborhood level.Conclusions: The results confirm that Ae. albopictus coexisted with Ae. aegypti in Mérida at the time of the study. The low relative abundance suggests that Ae. albopictus was in the initial phase of invasion.Introducción. El programa de enfermedades transmitidas por vectores en México tiene una red establecida de ovitrampas para la vigilancia entomológica de Aedes spp. Los servicios de salud del estado de Yucatán, en respuesta a reportes de Aedes albopictus en la periferia de Mérida, capital del estado, incrementaron la especificidad de dicha vigilancia.Objetivo. Describir la presencia y distribución de Ae. albopictus en Mérida y su abundancia relativa comparada con Aedes aegypti, en ovitrampas del programa de control de vectores.Materiales y métodos. Durante octubre de 2019, se seleccionaron al azar 91 ovitrampas en 31 barrios de Mérida. Los mosquitos adultos se obtuvieron del insectario de la Unidad Colaborativa para Bioensayos Entomológicos de la Universidad Autónoma de Yucatán a partir de huevos recolectados en campo. Se determinó la abundancia relativa de individuos adultos de cada especie identificada y por barrios evaluados.Resultados. En el 32 % de los barrios muestreados, se detectó Ae. albopictus y, en todos ellos, Ae. aegypti. Se recolectaron 28 adultos de Ae. albopictus (10 hembras y 18 machos) en las ovitrampas. No se observó correlación entre la abundancia de adultos ni de hembras Ae. aegypti y Ae. albopictus por barrio (p&gt;0,05).Conclusiones. Los resultados confirmaron que Ae. albopictus estaba coexistiendo con Ae. aegypti en Mérida en el momento del estudio. La baja abundancia relativa sugiere que Ae. albopictus se encontraba en la fase inicial de invasión

Impact of ITS on indoor <i>Aedes aegypti</i> adults.

<p>Comparison between treated (solid line) and untreated (broken line) clusters on the percentage of infested houses with <i>Ae</i>. <i>aegypti</i> (left) and their average abundance (right) in Merida, Yucatan, Mexico. The vertical dotted line represents the start of the intervention. The symbol ϴ denotes dates when the index was significantly different between ITS and control arms (with α = 0.05). Error bars show the standard error of the mean.</p

House screening with insecticide-treated netting provides sustained reductions in domestic populations of <i>Aedes aegypti</i> in Merida, Mexico

<div><p>Background</p><p>There is a need for effective methods to control <i>Aedes aegypti</i> and prevent the transmission of dengue, chikungunya, yellow fever and Zika viruses. Insecticide treated screening (ITS) is a promising approach, particularly as it targets adult mosquitoes to reduce human-mosquito contact.</p><p>Methodology/Principal findings</p><p>A cluster-randomised controlled trial evaluated the entomological efficacy of ITS based intervention, which consisted of the installation of pyrethroid-impregnated long-lasting insecticide-treated netting material fixed as framed screens on external doors and windows. A total of 10 treatment and 10 control clusters (100 houses/cluster) were distributed throughout the city of Merida, Mexico. Cross-sectional entomological surveys quantified indoor adult mosquito infestation at baseline (pre-intervention) and throughout four post-intervention (PI) surveys spaced at 6-month intervals corresponding to dry/rainy seasons over two years (2012–2014). A total of 844 households from intervention clusters (86% coverage) were protected with ITS at the start of the trial. Significant reductions in the indoor presence and abundance of <i>Ae</i>. <i>aegypti</i> adults (OR = 0.48 and IRR = 0.45, P<0.05 respectively) and the indoor presence and abundance of <i>Ae</i>. <i>aegypti</i> female mosquitoes (OR = 0.47 and IRR = 0.44, P<0.05 respectively) were detected in intervention clusters compared to controls. This high level of protective effect was sustained for up to 24 months PI. Insecticidal activity of the ITS material declined with time, with <i>~</i>70% mortality being demonstrated in susceptible mosquito cohorts up to 24 months after installation.</p><p>Conclusions/Significance</p><p>The strong and sustained entomological impact observed in this study demonstrates the potential of house screening as a feasible, alternative approach to a sustained long-term impact on household infestations of <i>Ae</i>. <i>aegypti</i>. Larger trials quantifying the effectiveness of ITS on epidemiological endpoints are warranted and therefore recommended.</p></div

Survival in cone bioassays.

<p>Mean of percentage (±SEM) of susceptible <i>Ae</i>. <i>aegypti</i> survival after exposure to ITS with different deployed times and levels of soiling.</p

Cone bioassays performed at 6, 12, 18 and 24 months post ITS installation.

<p>Results of WHO cone bioassays after 3 min. exposure: knockdown at 60 minutes (KD60) and 24 h mortality and their standard errors of mean (SE) are shown for New Orleans susceptible <i>Ae</i>. <i>aegypti</i> strain.</p

Location of treatment and control clusters within the city of Merida.

<p>The clusters with and without ITS are shown in blue and red, respectively. Source: INEGI, 2010 (<a href="http://www.beta.inegi.org.mx/app/biblioteca/ficha.html?upc=702825292805" target="_blank">http://www.beta.inegi.org.mx/app/biblioteca/ficha.html?upc=702825292805</a>).</p