Abstract
Insecticide resistance in malaria vectors threatens malaria prevention and control efforts. In Colombia the three primary vectors, Anopheles darlingi, An. nuneztovari s.l., and An. albimanus, have reported insecticide resistance to pyrethroids, organophosphates, carbamates, and DDT; however, the insecticide resistance monitoring is not continuous, and the data on the prevalence of resistance is scarce and geographically limited. We describe the resistance levels and intensity of previously detected resistant populations among primary malaria vectors from the most endemic malaria areas in Colombia. The study was carried out in 10 localities of five states in Colombia. Bioassays were carried out following the methodology of CDC Bottle Bioassay using the discriminating concentration and in order to quantify the intensity the specimens were exposed to 2, 5, and 10X discriminating concentrations. Five insecticides were tested: deltamethrin, lambda-cyhalothrin, alpha-cypermethrin, permethrin, and DDT. The results provide evidence of low resistance intensity and resistance highly localized to pyrethroids and DDT in key malaria vectors in Colombia. This may not pose a threat to malaria control yet but frequent monitoring is needed to follow the evolution of insecticide resistance.
Highlights
Since 2000, substantial progress has been made in fighting malaria
An. albimanus showed susceptibility to pyrethroids, for lambda-cyhalothrin the mortality was lower than 98% which is interpreted as possible resistance
The evidence of persistent insecticide resistance implies that at least annual monitoring is necessary in these localities, while the program is distributing long lasting insecticidal nets (LLINs) as the primary malaria vector control intervention
Summary
WHO estimates that between 2000 and 2015, malaria case incidence was reduced by 41% and malaria mortality rates by 62% [1, 2]. In 2016, there was an estimate of 216 million episodes of malaria and about 445,000 deaths globally, two-thirds of which were among children. Among the malaria-endemic countries in the WHO region of the Americas, Colombia contributed 15.3% of the total number of cases in 2016 and, in the last two years (2015-2016), the number of cases reported have doubled despite earlier reductions [3]. In relation to mosquito vectors, Anopheles albimanus, An. darlingi, and An. nuneztovari s.l. are widely distributed and are considered the primary vectors responsible for malaria transmission in most regions of the country [4]. In Colombia, the organochlorine insecticide DDT was intensively used for malaria control from 1947 until 1994 when its use was prohibited [5, 6]; since malaria vector control is supported mainly in the use of organophosphates
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