Abstract
BackgroundThe dramatic success of insecticide treated nets (ITNs) and long-lasting insecticidal nets (LLINs) in African countries has been countered by the rapid development of pyrethroid resistance in vector mosquitoes over the past decade. One advantage of the use of pyrethroids in ITNs is their excito-repellency. Use of the excito-repellency of pyrethroids might be biorational, since such repellency will not induce or delay the development of any physiological resistance. However, little is known about the relationship between the mode of insecticide resistance and excito-repellency in pyrethroid-resistant mosquitoes.MethodsDifferences in the reactions of 3 major malaria vectors in western Kenya to pyrethroids were compared in laboratory tests. Adult susceptibility tests were performed using World Health Organization (WHO) test tube kits for F1 progenies of field-collected An. gambiae s.s., An. arabiensis, and An. funestus s.s., and laboratory colonies of An. gambiae s.s. and An. arabiensis. The contact repellency to pyrethroids or permethrin-impregnated LLINs (Olyset® Nets) was evaluated with a simple choice test modified by WHO test tubes and with the test modified by the WHO cone bioassay test.ResultsField-collected An. gambiae s.s., An. arabiensis, and An. funestus s.s. showed high resistance to both permethrin and deltamethrin. The allelic frequency of the point mutation in the voltage-gated sodium channel (L1014S) in An. gambiae s.s. was 99.3–100%, while no point mutations were detected in the other 2 species. The frequency of takeoffs from the pyrethroid-treated surface and the flying times without contacting the surface increased significantly in pyrethroid-susceptible An. gambiae s.s. and An. arabiensis colonies and wild An. arabiensis and An. funestus s.s. colonies, while there was no significant increase in the frequency of takeoffs or flying time in the An. gambiae s.s. wild colony.ConclusionA different repellent reaction was observed in the field-collected An. gambiae s.s. than in An. arabiensis and An. funestus s.s. It might be that resistant mosquitoes governed by knockdown resistance (kdr) loose repellency to pyrethroids, whereas those lacking kdr maintain high repellency irrespective of their possessing metabolic resistance factors to pyrethroids. Further genetic evaluation is required for the demonstration of the above hypothesis.
Highlights
The dramatic success of insecticide treated nets (ITNs) and long-lasting insecticidal nets (LLINs) in African countries has been countered by the rapid development of pyrethroid resistance in vector mosquitoes over the past decade
Since the World Health Organization (WHO) adopted the use of long-lasting insecticidal nets (LLINs) as a principal strategy for effective malaria control in the Roll Back Malaria Partnership [2], pyrethroids have been the only class of insecticides used for LLINs [1,3]
The Mbita and Suba districts have been identified as high vector transmission areas in Kenya, and more than 50% of the population is exposed to malaria at a rate of ≥40% PfPR2–0 (Plasmodium falciparum parasite rate corrected to a standard age range of 2 to
Summary
The dramatic success of insecticide treated nets (ITNs) and long-lasting insecticidal nets (LLINs) in African countries has been countered by the rapid development of pyrethroid resistance in vector mosquitoes over the past decade. A dramatic success of insecticide treated nets (ITNs) and LLINs was recorded in African countries It has been countered by the rapid development of pyrethroid resistance in vector mosquitoes over the past decade [5]. L1014F mutations are widespread in western African countries, L1014S mutations are distributed in eastern Africa, and L1014F/ L1014S hybrids in An. gambiae s.s. are reported in the central region Such kdr mutations do not seem to be common in An. arabiensis Patton [8,9,10], but the metabolic resistance seems to be most common in this species [10,11]. The co-occurrence of these 2 resistance factors (metabolic and kdr) in a single mosquito population would lead to further threats to malaria control, since both factors might reinforce the resistance of each other
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