Evaluation of PermaNet 3.0 a deltamethrin-PBO combination net against Anopheles gambiae and pyrethroid resistant Culex quinquefasciatus mosquitoes: an experimental hut trial in Tanzania

Abstract

BackgroundCombination mosquito nets incorporating two unrelated insecticides or insecticide plus synergist are designed to control insecticide resistant mosquitoes. PermaNet 3.0 is a long-lasting combination net incorporating deltamethrin on the side panels and a mixture of deltamethrin and synergist piperonyl butoxide (PBO) on the top panel. PBO is an inhibitor of mixed function oxidases implicated in pyrethroid resistance.MethodAn experimental hut trial comparing PermaNet 3.0, PermaNet 2.0 and a conventional deltamethrin-treated net was conducted in NE Tanzania using standard WHOPES procedures. The PermaNet arms included unwashed nets and nets washed 20 times. PermaNet 2.0 is a long-lasting insecticidal net incorporating deltamethrin as a single active.ResultsAgainst pyrethroid susceptible Anopheles gambiae the unwashed PermaNet 3.0 showed no difference to unwashed PermaNet 2.0 in terms of mortality (95% killed), but showed differences in blood-feeding rate (3% blood-fed with PermaNet 3.0 versus 10% with PermaNet 2.0). After 20 washes the two products showed no difference in feeding rate (10% with 3.0 and 9% with 2.0) but showed small differences in mortality (95% with 3.0 and 87% with 2.0). Against pyrethroid resistant Culex quinquefasciatus, mediated by elevated oxidase and kdr mechanisms, the unwashed PermaNet 3.0 killed 48% and PermaNet 2.0 killed 32% but after 20 washes there was no significant difference in mortality between the two products (32% killed by 3.0 and 30% by 2.0). For protecting against Culex PermaNet 3.0 showed no difference to PermaNet 2.0 when either unwashed or after 20 washes; both products were highly protective against biting. Laboratory tunnel bioassays confirmed the loss of biological activity of the PBO/deltamethrin-treated panel after washing.ConclusionBoth PermaNet products were highly effective against susceptible Anopheles gambiae. As a long-lasting net to control or protect against pyrethroid resistant mosquitoes PermaNet 3.0 showed limited improvement over PermaNet 2.0 against Culex quinquefasciatus.

Efficacy of PermaNet® 3.0 and PermaNet® 2.0 nets against laboratory-reared and wild Anopheles gambiae sensu lato populations in northern Tanzania

“…This efficacy has also been observed in Ethiopia [9] and Cote d’Ivoire [18]. A similar study conducted in Muheza, Tanzania found that the personal protection rates for PermaNet® 3.0 and PermaNet® 2.0 washed 20 times were 71 and 73%, respectively [17]. The cause of these variations in the personal protection rate between and within the two PermaNet brands done in Tanzania are still not well understood.…”

“…These findings indicate that PermaNet® 2.0 and improved PermaNet® 3.0 (with PBO) are advanced tools for protection against resistant populations of An. gambiae mosquitoes [8, 17, 37]. This efficacy has also been observed in Ethiopia [9] and Cote d’Ivoire [18].…”

“…The experimental huts used in this trial were situated in Mabogini village, Moshi Rural District, northern Tanzania. They were constructed according to an East African experimental hut design first described elsewhere [17, 21]. The study area was chosen because of its high mosquito density throughout the year and a well-known status of insecticide resistance of the malaria vectors, An.…”

“…LLINs that use two unrelated insecticides or an insecticide plus a synergist have been shown to have increased efficacy against pyrethroid-resistant malaria vectors [17]. The incorporation of the synergist, piperonyl butoxide (PBO), in LLINs is able to significantly reduce or inhibit the enzymatic detoxification of insecticides, thus increasing the toxicity against mosquitoes [18].…”

Culminating anti-malaria efforts at long lasting insecticidal net?

“…Each insecticide has a distinct spectrum of insecticidal outcomes on mosquitoes, which imply that LLINs based on different insecticides may have different effects on mosquito vectors. Previous studies have suggested that LLINs elicited very low level of deterrence against susceptible mosquito vectors and were effective because they did not allow mosquitos to feed on the user [19,[21][22][23][24].…”