Abstract
BackgroundPhysiological characteristics (age and blood feeding status) of malaria vectors can influence their susceptibility to the current vector control tools that target their feeding and resting behaviour. To ensure the sustainability of the current and future vector control tools an understanding of how physiological characteristics may contribute to insecticide tolerance in the field is fundamental for shaping resistance management strategies and vector control tools. The aim of this study was to determine whether blood meal and mosquito age affect pyrethroid tolerance in field-collected Anopheles gambiae from western Kenya.MethodsWild mosquito larvae were reared to adulthood alongside the pyrethroid-susceptible Kisumu strain. Adult females from the two populations were monitored for deltamethrin resistance when they were young at 2–5 days old and older 14–16 days old and whether fed or unfed for each age group. Metabolic assays were also performed to determine the level of detoxification enzymes. Mosquito specimens were further identified to species level using the polymerase chain reaction (PCR) method.ResultsAnopheles gambiae sensu stricto was the predominant species comprising 96% of specimens and 2.75% Anopheles arabiensis. Bioassay results showed reduced pyrethroid induced mortality with younger mosquitoes compared to older ones (mortality rates 83% vs. 98%), independently of their feeding status. Reduced mortality was recorded with younger females of which were fed compared to their unfed counterparts of the same age with a mortality rate of 35.5% vs. 83%. Older blood-fed females showed reduced susceptibility after exposure when compared to unfed females of the same age (mortality rates 86% vs. 98%). For the Kisumu susceptible population, mortality was straight 100% regardless of age and blood feeding status. Blood feeding status and mosquito age had an effect on enzyme levels in both populations, with blood fed individuals showing higher enzyme elevations compared to their unfed counterparts (P < 0.0001). The interaction between mosquito age and blood fed status had significant effect on mosquito mortality.ConclusionThe results showed that mosquito age and blood feeding status confers increased tolerance to insecticides as blood feeding may be playing an important role in the toxicity of deltamethrin, allowing mosquitoes to rest on insecticide-treated materials despite treatment. These may have implications for the sustained efficacy of indoor residual spraying and insecticide-treated nets based control programmes that target indoor resting female mosquitoes of various gonotrophic status.
Highlights
Physiological characteristics of malaria vectors can influence their susceptibility to the current vector control tools that target their feeding and resting behaviour
Blood-fed female mosquitoes independent of age group recorded less than 50% knockdown within the 50 min exposure unlike their unfed counterparts from the same population (Fig. 1)
Though Kisumu strain was knockdown within the 60 min exposure, induction of tolerance due to blood feeding was observed in blood-fed females that recorded less than 80% knockdown within the 40 min exposure, unlike their unfed counterparts that recorded 100% knockdown within the 40 min exposure independent of age group (Fig. 1)
Summary
Physiological characteristics (age and blood feeding status) of malaria vectors can influence their susceptibility to the current vector control tools that target their feeding and resting behaviour. To ensure the sustainability of the current and future vector control tools an understanding of how physiological characteristics may contribute to insecticide tolerance in the field is fundamental for shaping resistance management strategies and vector control tools. The aim of this study was to determine whether blood meal and mosquito age affect pyrethroid tolerance in field-collected Anopheles gambiae from western Kenya. A major challenge facing the use of insecticides for malaria vector control is the development of insecticide resistance This has been reported in almost all countries of sub-Saharan Africa and may continue to threaten the sustainability of malaria strategies [3, 4]. In Kenya, the main malaria vector, An. gambiae sensu stricto (s.s.) is already showing high levels of resistance to pyrethroid insecticides, which are the mainstay of vector control in the country [5, 6]. Two main resistance mechanisms have been identified in An. gambiae s.s. mosquitoes in Kenya: insecticide target site insensitivity achieved by point mutations that render the actual targets of an insecticide less sensitive to the active ingredient [9,10,11], and metabolic resistance involving the sequestration, metabolism, and/or detoxification of the insecticide, largely through the overproduction of specific enzymes [5, 12]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
