A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria

Abstract

BackgroundThe vapor phase of the volatile pyrethroid transfluthrin incapacitates mosquitoes and prevents them from feeding. Although existing emanator products for delivering volatile pyrethroids protect against outdoor mosquito bites, they are too short-lived to be practical or affordable for routine use in low-income settings. New transfluthrin emanators, comprised simply of treated hessian fabric strips, have recently proven highly protective against outdoor-biting vectors of lymphatic filariasis, arboviruses and malaria, but their full protective lifespan, minimum dose requirements, and range of protection have not previously been assessed.MethodologyThe effects of transfluthrin-treated hessian strips upon mosquito biting exposure of users and nearby non-users, as well as dependence of protection upon treatment dose, were measured outdoors in rural Tanzania using human landing catches (HLC).Principal findingsStrips treated with 10ml of transfluthrin prevented at least three quarters (p < 0.001) of outdoor bites by Anopheles arabiensis, Culex spp. and Mansonia spp. mosquitoes, and >90% protection against bites on warmer nights with higher evaporation rates, for at least one year. Strips treated with this high dose also reduced biting exposure of non-users at a distance of up to 5m from the strips for An. arabiensis (p < 0.001) and up to 2m for Mansonia spp. (p = 0.008), but provided no protection to non-users against Culex spp. No evidence of increased risk for non-users, caused by diversion of mosquitoes to unprotected individuals, was found at any distance within an 80m radius. A dose of only 1ml provided equivalent protection to the 10ml dose against An. arabiensis, Culex spp. and Mansonia spp. mosquitoes over 6 months (p < 0.001).Conclusions/SignificanceTransfluthrin-treated hessian emanators provide safe, affordable, long-term protection against several different pathogen-transmitting mosquito taxa that attack humans outdoors, where they are usually active and cannot be protected by bed nets or residual sprays with conventional, solid-phase insecticides.

Developing an expanded vector control toolbox for malaria elimination

“…41 64 65 Encouragingly, one of the most widely used of these existing vapour-phase insecticides has recently been reformulated into low-technology emanator formats that provide protection lasting several months, at costs that should be affordable even in LMICs. [66][67][68] While transfluthrin, and several similarly volatile pyrethroids, are often described as spatial repellents, 60 69 they can actually incapacitate 65 or even kill mosquitoes. 70 They are therefore described here as vapour-phase insecticides, to distinguish them from repellents and irritants in the strict sense, which may be associated with considerable limitations, disadvantages and risks.…”

Measuring, manipulating and exploiting behaviours of adult mosquitoes to optimise malaria vector control impact

“…29 30 Following scale-up of LLINs, anthropophagic A. funestus became far more scarce and A. gambiae almost disappeared but A. arabiensis persisted 31 32 by exhibiting three behaviours which protect it against LLINs, as well as render it remarkably vulnerable to complementary measures: (1) increased feeding outdoors in the early evenings when people are active and unprotected by nets, 32 where they could now be targeted with insecticidetreated clothing 20 21 or vapour-phase insecticides; [22][23][24] (2) although they avoid fatal contact with LLINs when they do enter houses, 12 13 the fact is that bed nets force mosquitoes to enter twice as many houses to obtain the blood they need. 10 This phenomenon of repeated house entry could therefore be exploited to kill them more effectively than would otherwise be possible, by applying additional insecticides inside houses by spraying them on the walls as IRS (figure 1), or by targeting them to entry points with eave tubes 19 or exit points with eave baffles 17 ; and (3) half of their blood meals are now obtained from unprotected cattle 34 that do not use nets but could be readily treated with long-lasting veterinary insecticide formulations.…”

“…28 As illustrated mechanistically in figure 2, such layering of interventions in a logical sequence can enable rational manipulation and exploitation of mosquito behaviour patterns, sometimes referred to as 'push-pull' strategies [35][36][37][38] that originate from the agriculture sector. 39 Such altered postintervention behavioural patterns create new opportunities for targeting outdoorfeeding vectors with insecticide clothing treatments, 18 19 insecticide vapour emanators [22][23][24] and/or veterinary insecticides 28 that would previously have been ineffective. These intervention options can therefore be expected to have a much greater impact on residual transmission as second-line and third-line measures to supplement LLINs in an elimination programme than they ever could on baseline transmission as the first-line measure in a control programme.…”

Evaluation of personal protection afforded by repellent-treated sandals against mosquito bites in south-eastern Tanzania

“…There are several formats through which spatial repellents are dispensed, such as mosquito coils, vaporizer mats and liquid vaporizers [24,35,36]. Recently, an alternative emanator delivery format for volatilizing transfluthrin at ambient temperatures have proven efficacious against mosquito bites [37][38][39][40][41]. Although effective, these emanator formats require that the host is confined to a protected air space, therefore, limiting mobility [38][39][40].…”

“…Recently, an alternative emanator delivery format for volatilizing transfluthrin at ambient temperatures have proven efficacious against mosquito bites [37][38][39][40][41]. Although effective, these emanator formats require that the host is confined to a protected air space, therefore, limiting mobility [38][39][40]. In order to impact outdoor biting, spatial repellents delivery formats must be optimized to protect users wherever they are outdoors [42].…”