Insecticide resistance profile of Anopheles gambiae from a phase II field station in Cové, southern Benin: implications for the evaluation of novel vector control products

Abstract

BackgroundNovel indoor residual spraying (IRS) and long-lasting insecticidal net (LLIN) products aimed at improving the control of pyrethroid-resistant malaria vectors have to be evaluated in Phase II semi-field experimental studies against highly pyrethroid-resistant mosquitoes. To better understand their performance it is necessary to fully characterize the species composition, resistance status and resistance mechanisms of the vector populations in the experimental hut sites.MethodsBioassays were performed to assess phenotypic insecticide resistance in the malaria vector population at a newly constructed experimental hut site in Cové, a rice growing area in southern Benin, being used for WHOPES Phase II evaluation of newly developed LLIN and IRS products. The efficacy of standard WHOPES-approved pyrethroid LLIN and IRS products was also assessed in the experimental huts. Diagnostic genotyping techniques and microarray studies were performed to investigate the genetic basis of pyrethroid resistance in the Cové Anopheles gambiae population.ResultsThe vector population at the Cové experimental hut site consisted of a mixture of Anopheles coluzzii and An. gambiae s.s. with the latter occurring at lower frequencies (23 %) and only in samples collected in the dry season. There was a high prevalence of resistance to pyrethroids and DDT (>90 % bioassay survival) with pyrethroid resistance intensity reaching 200-fold compared to the laboratory susceptible An. gambiae Kisumu strain. Standard WHOPES-approved pyrethroid IRS and LLIN products were ineffective in the experimental huts against this vector population (8–29 % mortality). The L1014F allele frequency was 89 %. CYP6P3, a cytochrome P450 validated as an efficient metabolizer of pyrethroids, was over-expressed.ConclusionCharacterizing pyrethroid resistance at Phase II field sites is crucial to the accurate interpretation of the performance of novel vector control products. The strong levels of pyrethroid resistance at the Cové experimental hut station make it a suitable site for Phase II experimental hut evaluations of novel vector control products, which aim for improved efficacy against pyrethroid-resistant malaria vectors to WHOPES standards. The resistance genes identified can be used as markers for further studies investigating the resistance management potential of novel mixture LLIN and IRS products tested at the site.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0981-z) contains supplementary material, which is available to authorized users.

A Chlorfenapyr Mixture Net Interceptor® G2 Shows High Efficacy and Wash Durability against Resistant Mosquitoes in West Africa

“…This low mortality response is typical of other pyrethroid-only LN evaluated in Benin and is because the main vector species An . coluzzii has developed high-level resistance to alpha-cypermethrin (207 fold) through a combination of L1014F kdr and CYP6P3 P450 mechanisms [8, 9]. Such was the strength of the resistance that a 10-fold difference in the surface content of alpha-cypermethrin between the unwashed and 20-times washed Interceptor ® LN made little or no difference to the poor efficacy of the net or to the high proportion of mosquitoes surviving (82% and 89% over 20 washes).…”

“…While Interceptor G2 would continue to provide personal protection to individual users in pyrethroid resistant areas it is recommended that deployment is done to universal coverage so entire villages can benefit from the community protection which arises from the mass killing of mosquito populations when an effective LN is taken to scale and which a standard pyrethroid-only LN would no longer provide. Beyond Benin, deployment of the mixture LN should extend and restore effectiveness in the many places being compromised by resistance mediated by kdr in combination with metabolic mechanisms [3–5, 9, 25]. …”

“…The vector species are Anopheles coluzzii (formerly An gambiae M form) and An . gambiae s.s. (S form) [9]. The frequency of the 1014F kdr allele is 89% and the P450 CYP6P3 associated with metabolic resistance is also present.…”

“…Of the 42 African countries deploying LN, pyrethroid resistance was reported in 29 countries in 2010–2015. While a negative epidemiological impact of pyrethroid resistance on malaria control has yet to be confirmed [1, 4], an increasing number of reports show that pyrethroid resistance is capable of reducing the effectiveness of LNs used against host seeking mosquitoes [5–7], and leading brands are giving less personal protection and reduced vector mortality rates compared to areas of pyrethroid susceptibility [8, 9]. …”

A bibliometric analysis of literature on malaria vector resistance: (1996 – 2015)

“…Most important challenges are the emergence of resistance to the new generation antimalarial drug resistance, artemisinins and the emergence of resistance among malaria vectors to common insecticides [12][13][14][15][16][17][18][19]. Insecticide resistance in malaria vectors is becoming a global concern because of reports on insecticide resistance from many countries in Africa [20][21][22][23][24]. Of particular concern is vector resistance to pyrethroids since they are the only class of insecticides approved for use in ITNs.…”