Impact of insecticide-treated nets on wild pyrethroid resistant Anopheles epiroticus population from southern Vietnam tested in experimental huts

An experimental station, based on the model of West Africa and adapted to the behaviour of the target species, was built in southern Vietnam. The study design was adapted from the WHO phase 2 guidelines. The study arms included a conventionally treated polyester net (CTN) with deltamethrin washed just before exhaustion, the WHO recommended long-lasting insecticidal net (LLIN) PermaNet 2.0？ unwashed and 20 times washed and PermaNet 3.0？, designed for the control of pyrethroid resistant vectors, unwashed and 20 times washed.The nets still provided personal protection against the resistant An. epiroticus population. The personal protection ranged from 67% for deltamethrin CTN to 85% for unwashed PermaNet 3.0. Insecticide resistance in the An. epiroticus mosquitoes did not seem to alter the deterrent effect of pyrethroids. A significant higher mortality was still observed among the treatment arms despite the fact that the An. epiroticus population is resistant against the tested insecticides.This study shows that CTN and LLINs still protect individuals against a pyrethroid resistant malaria vector from the Mekong region, where insecticide resistance is caused by a metabolic mechanism. In the light of a possible elimination of malaria from the Mekong region these insights in operational consequences of the insecticide resistance on control tools is of upmost importance.Insecticide resistance has been demonstrated in many African and Asian malaria vectors [1,2]. The impact of the observed resistance on the applied control tools will depend on the mechanism(s) conferring resistance, the biology of the vector and the control method applied. Evidence exists that resistance reduces the efficacy of indoor residual spraying (IRS). In South Africa, for example, increased levels of mixed function oxidases in Anopheles funestus was associated with malaria control failure [3]. On the island Bioko, Equatorial Guinea, IRS with pyrethroids failed to reduce the pyrethroid resistant Ano