Small-scale field evaluation of push-pull system against early- and outdoor-biting malaria mosquitoes in an area of high pyrethroid resistance in Tanzania

Abstract

Background: Despite high coverage of indoor interventions like insecticide-treated nets, mosquito-borne infections persist, partly because of outdoor-biting, early-biting and insecticide-resistant vectors. Push-pull systems, where mosquitoes are repelled from humans and attracted to nearby lethal targets, may constitute effective complementary interventions. Methods: A partially randomized cross-over design was used to test efficacy of push-pull in four experimental huts and four local houses, in an area with high pyrethroid resistance in Tanzania. The push-pull system consisted of 1.1% or 2.2% w/v transfluthrin repellent dispensers and an outdoor lure-and-kill device (odour-baited mosquito landing box). Matching controls were set up without push-pull. Adult male volunteers collected mosquitoes attempting to bite them outdoors, but collections were also done indoors using exit traps in experimental huts and by volunteers in the local houses. The collections were done hourly (1830hrs-0730hrs) and mosquito catches compared between push-pull and controls. An. gambiae s.l. and An. funestus s.l. were assessed by PCR to identify sibling species, and ELISA to detect Plasmodium falciparum and blood meal sources. Results: Push-pull in experimental huts reduced outdoor-biting for An. arabiensis and Mansonia species by 30% and 41.5% respectively. However, the reductions were marginal and insignificant for An. funestus (12.2%; p>0.05) and Culex (5%; p>0.05). Highest protection against all species occurred before 2200hrs. There was no significant difference in number of mosquitoes inside exit traps in huts with or without push-pull. In local households, push-pull significantly reduced indoor and outdoor-biting of An. arabiensis by 48% and 25% respectively, but had no effect on other species. Conclusion: This push-pull system offered modest protection against outdoor-biting An. arabiensis, without increasing indoor mosquito densities. Additional experimentation is required to assess how transfluthrin-based products affect mosquito blood-feeding and mortality in push-pull contexts. This approach, if optimised, could potentially complement existing malaria interventions even in areas with high pyrethroid resistance.

Evaluation of a push–pull system consisting of transfluthrin-treated eave ribbons and odour-baited traps for control of indoor- and outdoor-biting malaria vectors

“…They however also concluded that mosquito biting protection was mainly offered by the push-subunits, which is similar to the findings of this current study [38]. Additionally, during a recent small-scale field evaluations of push–pull, it was determined that presence of the system at the peri-domestic areas undermined the effects of the odor-baited mosquito landing box (MLB) [14]. However, testing both push-and-pull subunits in this current study did not affect the indoor mosquito biting protection, as this was mainly offered by the push-subunits alone.…”

Eave ribbons treated with the spatial repellent, transfluthrin, can effectively protect against indoor-biting and outdoor-biting malaria mosquitoes

“…The levels of protective efficacy demonstrated by the treated eave ribbons in this study, could potentially be further improved by adding odour-baited traps or lure and kill technologies so as to achieve high levels of communal level protection beyond the household and personal protection currently observed. Indeed, this has already been demonstrated in small-scale in push–pull approaches [ 43 , 44 ]. A study by Menger et al demonstrated that such push–pull effects may however be greater at community level than in the peri-domestic areas [ 43 ], most likely because of the traps, when placed near houses lure the mosquitoes to the area, potentially increasing risk in the peridomestic space, and but the trapped mosquitoes are killed, thereby reducing overall risk at community level overtime.…”

“…This too is in line with a previous study, which involved using the transfluthrin actively dispensed at the peri-domestic areas in a push–pull approach whereby the approach did not significantly reduce An. funestus biting and it increased possibility of mosquito diversion effect [ 44 ]. The unresponsiveness of An.…”

Semi-field evaluation of freestanding transfluthrin passive emanators and the BG sentinel trap as a “push-pull control strategy” against Aedes aegypti mosquitoes

“…The likely reason for this is the poor response of mosquitoes to the BGS in the presence of humans. Numerous previous studies on push-pull technologies have demonstrated the higher efficacy of the push than the pull [14,[27][28][29]. While the push-pull system may need further development, the success of the FTPE was encouraging and indicated their potential for the control of arboviral diseases.…”