Mixture for Controlling Insecticide-Resistant Malaria Vectors

Abstract

The spread of resistance to pyrethroids in the major Afrotropical malaria vectors Anopheles gambiae s.s. necessitates the development of new strategies to control resistant mosquito populations. To test the effi cacy of nets treated with repellent and insecticide against susceptible and insecticideresistant An. gambiae mosquito populations, we impregnated mosquito bed nets with an insect repellent mixed with a low dose of organophosphorous insecticide and tested them in a rice-growing area near Bobo-Dioulasso, Burkina Faso. During the fi rst 2 weeks posttreatment, the mixture was as effective as deltamethrin alone and was more effective at killing An. gambiae that carried knockdown resistance (kdr) or insensitive acetylcholinesterase resistance (Ace1 R ) genes. The mixture seemed to not kill more susceptible genotypes for the kdr or Ace1 R alleles. Mixing repellents and organophosphates on bed nets could be used to control insecticideresistant malaria vectors if residual activity of the mixture is extended and safety is verifi ed. P yrethroids are the only class of insecticides that are recommended by the World Health Organization (WHO) and the Centers for Disease Control and Prevention for net impregnation to control malaria transmission (1,2). Unfortunately, malaria vector resistance to pyrethroids is becoming widespread across Africa. Pyrethroid resistance mechanisms can be divided into 2 groups: metabolic (alterations in the expression levels of activities of detoxifi cation enzymes) and target site (nonsilent point mutations within structural receptor genes, e.g., knockdown resistance [kdr] mutations) (3). Whether the spread of resistance genes will pose a serious threat to vector control programs that are based uniquely on pyrethroid use is uncertain. Some studies have shown that kdr resistance does not decrease the level of protection conferred by insecticide-treated nets (ITNs) (4) and that ITNs do not induce kdr selection (5). Conversely, more recent studies have reported a fi tness advantage for kdr-resistant phenotypes (6) and decreased effi cacy of ITNs in an area of pyrethroid resistance in Benin (7). The need for alternative insecticidal molecules is becoming increasingly clear; however, fewer novel active ingredients are available and the timeframe needed to satisfy the regulatory requirements of public health formulations is exceedingly long (8). Thus, the only option for managing insecticide resistance in malaria vectors is optimal use of existing compounds. Two such tactics have already been explored: 1) the alternating use of different classes of insecticides by rotation of active ingredients and mosaic treatments (9,10), and 2) the use of insecticide mixtures (10,11).We tested the ability of existing ingredients, a mixture of insect repellents and nonpyrethroid insecticides, to achieve vector death and excito-repellency (irritancy when mosquito contacts net and repellent activity in air) (12). The rationale behind this concept is that nonpyrethroid compounds can mimic the original features of...

Indoor Use of Plastic Sheeting Impregnated with Carbamate Combined with Long-Lasting Insecticidal Mosquito Nets for the Control of Pyrethroid-Resistant Malaria Vectors

“…35 The use of synergists (e.g ., piperonyl butoxide [PBO]) to improve the efficacy of LLIN 29,36 should be further explored. Integrated approaches for malaria vector control, either by mixing two unrelated insecticides (including synergists) on the same substrates 15,25 or combining spatially different interventions within dwellings (LLIN + IRS-like treatments), also represent key options for the management of insecticide resistance in malaria-endemic areas. This later strategy is currently being investigated in south Benin through a randomized controlled trial to assess the impact of LLIN alone and in combination with CTPS on malaria incidence and transmission as well as the management of insecticide resistance of malaria vectors.…”

“…The experimental hut trial was carried out at the Vallée du Kou (VK7), a huge rice field area located near BoboDioulasso, Burkina Faso, 15 between October and December 2008. Both molecular M and S forms of An.…”

“…Both untreated and PermaNet 2.0 were deliberately holed (six holes, 4 × 4 cm each) to simulate torn nets. 15 The carbamate used for the treatment of the plastic sheeting (CTPS) and walls (IRS) was bendiocarb wetable powder (WP) concentrate 80W (Ficam) at a single dose of 400 mg active ingredients (ai) /m 2 . Ficam and the resin were provided by Bayer (Leverkusen, Germany).…”

Synergy between Repellents and Organophosphates on Bed Nets: Efficacy and Behavioural Response of Natural Free-Flying An. gambiae Mosquitoes

“…A companion study showed that these two mixtures are more efficient than conventional pyrethroid-treated nets against susceptible and resistant An. gambiae populations and did not induce any additional selective pressure on the resistance genes, Ace1 R and Kdr [15]. Criticisms on this new strategy of resistant malaria vector control focused on the short residual effect of the repellents [29].…”

Insecticide and Repellent Mixture Pour-On Protects Cattle against Animal Trypanosomosis

“…This is the case for Vectoclor that contained three times less cypermethrin than Cypertraz (i.e 5g/l against 15g/l). Insecticides and repellent mixtures have also been successfully used in public health against mosquitoes that present increasing levels of insecticide resistance, and this combination proved highly effective [43, 44]. This is also the case for the Vectoclor combination that has been shown to be effective against the invasive and multi resistant ticks Rhipicephalus (Boophilus) microplus [15, 45].…”