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

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. 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. 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. 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.

尽管经杀虫剂处理蚊帐（insecticide-treated nets）等室内蚊虫防控干预措施覆盖率极高，但蚊媒传染病仍持续流行，这在一定程度上归因于媒介蚊虫的户外吸血、提前吸血行为以及杀虫剂抗性。推拉防控系统（push-pull systems）作为一类将蚊虫驱离人类宿主，并将其诱集至周边致死性诱杀靶标的防控策略，或可成为现有疟疾防控手段的有效补充方案。本研究采用半随机交叉试验设计，在坦桑尼亚一处存在高水平拟除虫菊酯抗性（pyrethroid resistance）的区域，于4间实验小屋及4栋当地居民住宅中评估该推拉系统的防控效果。该推拉系统由1.1%或2.2%质量体积比（w/v）的四氟甲醚菊酯（transfluthrin）缓释驱避装置，以及一套户外气味诱杀蚊箱（odour-baited mosquito landing box）组成。同时设置无推拉系统的匹配对照组。成年男性志愿者负责采集试图在户外叮咬他们的蚊虫；同时在实验小屋内通过出口诱捕器（exit traps）、在当地居民住宅中由志愿者采集室内蚊虫。采样时段为每小时1次，覆盖1830时至次日0730时，随后对比推拉系统组与对照组的蚊虫捕获量。采用聚合酶链反应（PCR）对冈比亚按蚊复合体（An. gambiae s.l.）和凶小按蚊复合体（An. funestus s.l.）进行姐妹种鉴定，并通过酶联免疫吸附试验（ELISA）检测样本中恶性疟原虫（Plasmodium falciparum）感染情况及蚊虫血源。实验小屋中的推拉系统可使阿拉伯按蚊（An. arabiensis）和曼蚊属（Mansonia）的户外吸血比例分别降低30%和41.5%。但该系统对凶小按蚊复合体（12.2%；P>0.05）和库蚊属（Culex）的防控效果微弱且无统计学意义。在当日2200时前，该系统对各类蚊虫的防护效果达到最佳。无论是否部署推拉系统，实验小屋出口诱捕器内的蚊虫数量均无显著差异。在当地居民住宅中，推拉系统可使阿拉伯按蚊的室内及户外吸血行为分别显著减少48%和25%，但对其他蚊种无明显防控效果。该推拉系统可对户外吸血的阿拉伯按蚊提供适度防护，且未提升室内蚊虫密度。未来需开展额外实验，以评估基于四氟甲醚菊酯的产品在推拉防控场景中对蚊虫吸血行为及死亡率的影响。若该策略得以优化，即便在拟除虫菊酯抗性高发区域，也有望成为现有疟疾防控手段的有效补充。