Seasonal and geographic variation in insecticide resistance in Aedes aegypti in southern Ecuador

Abstract

Insecticide resistance (IR) can undermine efforts to control vectors of public health importance. Aedes aegypti is the main vector of resurging diseases in the Americas such as yellow fever and dengue, and recently emerging chikungunya and Zika fever, which have caused unprecedented epidemics in the region. Vector control remains the primary intervention to prevent outbreaks of Aedes-transmitted diseases. In many high-risk regions, like southern Ecuador, we have limited information on IR. In this study, Ae. aegypti IR was measured across four cities in southern Ecuador using phenotypic assays and genetic screening for alleles associated with pyrethroid IR. Bottle bioassays showed significant inter-seasonal variation in resistance to deltamethrin, a pyrethroid commonly used by the Ministry of Health, and alpha-cypermethrin, as well as between-city differences in deltamethrin resistance. There was also a significant difference in phenotypic response to the organophosphate, Malathion, between two cities during the second sampling season. Frequencies of the resistant V1016I genotype ranged from 0.13 to 0.68. Frequencies of the resistant F1534C genotype ranged from 0.63 to 1.0, with sampled populations in Machala and Huaquillas at fixation for the resistant genotype in all sampled seasons. In Machala and Portovelo, there were statistically significant inter-seasonal variation in genotype frequencies for V1016I. Resistance levels were highest in Machala, a city with hyperendemic dengue transmission and historically intense insecticide use. Despite evidence that resistance alleles conferred phenotypic resistance to pyrethroids, there was not a precise correspondence between these indicators. For the F1534C gene, 17.6% of homozygous mutant mosquitoes and 70.8% of heterozygotes were susceptible, while for the V1016I gene, 45.6% homozygous mutants and 55.6% of heterozygotes were susceptible. This study shows spatiotemporal variability in IR in Ae. aegypti populations in southern coastal Ecuador, and provides an initial examination of IR in this region, helping to guide vector control efforts for Ae. aegypti. Author SummaryMosquito control is the primary method of managing the spread of many diseases transmitted by the yellow fever mosquito (Aedes aegypti). Throughout much of Latin America the transmission of diseases like dengue fever and Zika fever pose a serious risk to public health. The rise of insecticide resistance (IR) is a major threat to established vector control programs, which may fail if commonly used insecticides are rendered ineffective. Public health authorities in southern coastal Ecuador, a high-risk region for diseases vectored by Ae. aegypti, previously had limited information on the status of IR in local populations of mosquitoes. Here, we present the first assessment of IR in adult Ae. aegypti to insecticides (deltamethrin, Malathion, and alphacypermethrin) routinely used in public health vector control in four cities along Ecuador's southern coast. Observed patterns of IR differed between cities and ...

Co-occurrence of kdr mutations V1016I and F1534C in pyrethroid-resistant Aedes aegypti (Diptera: Culicidae) populations from Costa Rica

“…aegypti populations, including a population from Guanacaste province, Costa Rica (Saavedra-Rodriguez et al 2007). Although, functional conformation experiments do not confirm the role of the V1016I mutation in pyrethroid resistance, many studies have correlated the presence of this mutation to phenotypic resistance (Deming et al 2016, Brito et al 2018, Maestre-Serrano et al 2019, Ryan et al 2019). In contrast, kdr mutation F1534C has been strongly associated with DDT and pyrethroid resistance and confirmed by functional experiments in Xenopus oocytes (Du et al 2013).…”

The need to harmonize insecticide resistance testing: methodology, intensity concentrations and molecular mechanisms evaluated inAedes aegyptipopulations in Central America and Hispaniola

“…In America, kdr mutations have been reported in Ae. aegypti populations from Ecuador, (22), United States (23, 24), Colombia (25, 26), México (27–29), Brazil (30–35), Lesser Antilles (36–40), French Guiana (37), Venezuela (29, 41), Cuba (29, 39), Panamá (42), Puerto Rico (43). This is the first report of kdr mutations for the countries included in this study, except for Haiti (87).…”