Biochemical basis of permethrin resistance in Anopheles arabiensis from Lower Moshi, north-eastern Tanzania.

Johnson Matowo,Jovin A Kitau,Mark Rowland,Filemoni Tenu,Manisha A Kulkarni,Franklin W Mosha,Richard M Oxborough

doi:10.1186/1475-2875-9-193

Abstract

BackgroundDevelopment of resistance to different classes of insecticides is a potential threat to malaria control. With the increasing coverage of long-lasting insecticide-treated nets in Tanzania, the continued monitoring of resistance in vector populations is crucial. It may facilitate the development of novel strategies to prevent or minimize the spread of resistance. In this study, metabolic-based mechanisms conferring permethrin (pyrethroid) resistance were investigated in Anopheles arabiensis of Lower Moshi, Kilimanjaro region of north-eastern Tanzania.MethodsWHO susceptibility test kits were used to detect resistance to permethrin in An. arabiensis. The levels and mechanisms of permethrin resistance were determined using CDC bottle bioassays and microplate (biochemical) assays. In bottle bioassays, piperonyl butoxide (PBO) and s,s,s-tributyl phosphorotrithioate (DEF) were used as synergists to inhibit mixed function oxidases and non-specific esterases respectively. Biochemical assays were carried out in individual mosquitoes to detect any increase in the activity of enzymes typically involved in insecticide metabolism (mixed function oxidases, α- and β-esterases).ResultsAnopheles arabiensis from the study area was found to be partially resistant to permethrin, giving only 87% mortality in WHO test kits. Resistance ratios at KT50 and KT95 were 4.0 and 4.3 respectively. The permethrin resistance was partially synergized by DEF and by PBO when these were mixed with permethrin in bottle bioassays and was fully synergized when DEF and PBO were used together. The levels of oxidase and β-esterase activity were significantly higher in An. arabiensis from Lower Moshi than in the laboratory susceptible strain. There was no difference in α-esterase activity between the two strains.ConclusionElevated levels of mixed function oxidases and β-esterases play a role in detoxification of permethrin in the resistant An. arabiensis population of Lower Moshi.

Highlights

Development of resistance to different classes of insecticides is a potential threat to malaria control
Anopheline mosquitoes in many parts of Africa have become resistant to pyrethroids, partly in response to agricultural application or run off of insecticides into mosquito breeding sites [2,4,5,6], but increasingly in response to selection pressure resulting from the scaling up of longlasting insecticide-treated nets and indoor residual
The aim of this study was to investigate the biochemical mechanisms of permethrin resistance in field populations of An. arabiensis from Lower Moshi in Kilimanjaro region of north-eastern Tanzania

Summary

Introduction

Development of resistance to different classes of insecticides is a potential threat to malaria control. With the increasing coverage of long-lasting insecticide-treated nets in Tanzania, the continued monitoring of resistance in vector populations is crucial. It may facilitate the development of novel strategies to prevent or minimize the spread of resistance. There are two broad mechanisms by which insect pests develop resistance to insecticides They may produce increased quantities of enzymes, which either metabolize the insecticide or sequestrate the molecules so they cannot function. The second mechanism involves mutation of the insecticide target-site This effectively blocks the action of the insecticide. Both types of mechanism have been studied in various species of insects [12,13,14,15,16]

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