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

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.

Insecticide resistance and its underlying mechanisms in field populations of Aedes aegypti adults (Diptera: Culicidae) in Singapore

“…Unlike a dose/response test, it requires fewer individuals for toxicity evaluation. Knockdown time (KT 50 ), which is the time required for 50% of individuals to be knocked down was used compared to lethal concentration (LC 50 ) for resistance when resistance is recessive or present in low frequency [18]. The longer exposure period (3 h instead of 1 h) was used in all pyrethroid bioassays because preliminary tests showed that no knockdown occurred within 1 h. Mosquitoes were held for 24 h in the holding tube after exposure before mortality was recorded.…”

Malaria entomological profile in Tanzania from 1950 to 2010: a review of mosquito distribution, vectorial capacity and insecticide resistance

“…The biochemical basis of permethrin resistance in An. arabiensis from Lower Moshi, with elevated levels of mixed function oxidases and ß-esterases has been registered (Matowo, et al, 2010). A low frequency of West African kdr (L104F) was detected in Moshi (Kulkarni et al, 2006b).…”

“…Only five studies reported data on insecticide resistance for malaria vectors in Tanzania (Mnzava, 1991;Kulkarni et al, 2006bKulkarni et al, , 2007Matowo et al, 2010; WHO/GATES VBC project unpublished report). Of these, two were from countrywide surveys, while the rest were localized.…”

“…Kabula et al, unpublished) and An. arabiensis (Kulkarni et al, 2006;Matowo et al, 2010). The insecticides tested were permethrin, deltamethrin, Lambacyhalothrin and DDT.…”

Knock down efficacy of commercially available insecticides against Anopheles gambiae

“…The emergence and spread of insecticide resistance to major classes of insecticides in some areas is threatening the success of vectorborne disease control programs [13,14,15,16]. Several efficacy studies on pyrethroid insecticides used in impregnation of bed nets and curtains have been carried out.…”