Experimental hut evaluation of a novel long-lasting non-pyrethroid durable wall lining for control of pyrethroid-resistant Anopheles gambiae and Anopheles funestus in Tanzania

Abstract

BackgroundA novel, insecticide-treated, durable wall lining (ITWL), which mimics indoor residual spraying (IRS), has been developed to provide prolonged vector control when fixed to the inner walls of houses. PermaNet® ITWL is a polypropylene material containing non-pyrethroids (abamectin and fenpyroximate) which migrate gradually to the surface.MethodsAn experimental hut trial was conducted in an area of pyrethroid-resistant Anopheles gambiae s.l. and Anopheles funestus s.s. to compare the efficacy of non-pyrethroid ITWL, long-lasting insecticidal nets (LLIN) (Interceptor®), pyrethroid ITWL (ZeroVector®), and non-pyrethroid ITWL + LLIN.ResultsThe non-pyrethroid ITWL produced relatively low levels of mortality, between 40–50% for An. funestus and An. gambiae, across all treatments. Against An. funestus, the non-pyrethroid ITWL when used without LLIN produced 47% mortality but this level of mortality was not significantly different to that of the LLIN alone (29%, P = 0.306) or ITWL + LLIN (35%, P = 0.385). Mortality levels for An. gambiae were similar to An. funestus with non-pyrethroid ITWL, producing 43% mortality compared with 26% for the LLIN. Exiting rates from ITWL huts were similar to the control and highest when the LLIN was present. An attempt to restrict mosquito access by covering the eave gap with ITWL (one eave open vs four open) had no effect on numbers entering. The LLIN provided personal protection when added to the ITWL with only 30% blood-fed compared with 69 and 56% (P = 0.001) for ITWL alone. Cone bioassays on ITWL with 30 min exposure after the trial produced mortality of >90% using field An. gambiae. ConclusionsDespite high mortality in bioassays, the hut trial produced only limited mortality which was attributed to pyrethroid resistance against the pyrethroid ITWL and low efficacy in the non-pyrethroid ITWL. Hut ceilings were left uncovered and may have served as a potential untreated refuge. By analogy to IRS campaigns, which also do not routinely treat ceilings, high community coverage with ITWL may still reduce malaria transmission. Restriction of eave gaps by 75% proved an inadequate barrier to mosquito entry. The findings represent the first 2 months after installation and do not necessarily predict long-term efficacy.

Experimental huts trial of the efficacy of pyrethroids/piperonyl butoxide (PBO) net treatments for controlling multi-resistant populations of Anopheles funestus s.s. in Kpomè, Southern Benin

“…A more recent study conducted by Malima et al . 69 in an area where An. funestus is resistant to pyrethroid, showed that even when non-pyrethroid insecticide-treated nets with durable wall lining (ITWL) are used, this cannot guarantee up to 50% protection against resistant An.…”

Impact of non-pyrethroid insecticide treated durable wall lining on age structure of malaria vectors in Muheza, Tanzania

“…Our findings concur with a study conducted in the experimental huts which found that, the presence of both LLINs and non-pyrethroid ITWL have led to a significant increase the proportions of An. gambiae s. l. exiting the huts [ 17 ]. This situation has implication in reduction of malaria transmission in a malaria-endemic community [ 34 ].…”

“…Similar findings have also reported from the same area that, significantly higher proportions of An. funestus exited through the exit trap due to the presence of pyrethroid LLINs compared to non-pyrethroid ITWL [ 17 ]. ITWL intervention has some positive practical implications as they are durable and cost effective compared to the IRS and also it improves houses in rural settings where most of the walls are made up of mud [ 18 ].…”

“…Currently, a novel non-pyrethroid insecticide treated durable wall liner (ITWL) which works similar to IRS has been developed. It consists of a thin sheet of cloth made from high-density polypropylene treated with a mixture of two non-pyrethroid insecticides namely; abamectin and fenpyroximate [ 17 , 18 ]. The impact of ITWL intervention on age structure of malaria vectors is not well known in Tanzania.…”

A Roadmap for the Development of Ivermectin as a Complementary Malaria Vector Control Tool

“…To prevent mosquito resistance, early research into optimal combination with other vector control approaches should be performed; in addition, attention to other potential uses of ivermectin, both for NTDs as well as malaria, that could increase the exposure and hasten the appearance of resistance, such as ivermectin-based sugar baits 87,88 or wall linings, 89 should be discussed and evaluated as part of risk management.…”