マリでの魅力的なターゲットを絞ったシュガーベイト試験

The current dominant malaria vector control tools remain critically important and have saved many lives. Yet, they are not well-suited for malaria vectors that avoid contact with indoor insecticides by predominantly biting outdoors, by frequently biting animals, and by resting outdoors or remaining within houses only briefly when they do enter. These behaviors allow residual populations of vector mosquitoes to survive, expand, and to increasingly contribute to malaria transmission, despite high coverage. These vectors can sustain endemic transmission even if they rarely bite humans. An. arabiensis is a particularly important source of persistent residual transmission despite Long Lasting Insecticide-treated Net (LLIN) scale-up; this mosquito prefers to feed on animals, and, often bites and rests outside, and has limited indoor exposure. There is need for new vector control tools to target residual outdoor transmission.

In addition to the biological need for female Anopheles species to take a blood meal to obtain protein necessary for egg production, all Anopheles must feed regularly and frequently on liquid and carbohydrates (sugars) to survive. Common sources of liquid and sugar meals include plant tissue and floral nectar. Mosquitoes are guided to sugar sources by chemical attractants. The Attractive Target Sugar Baits (ATSBs) is designed specifically to attract the mosquito with a source of liquid and sugar and include an ingestion toxicant to then kill the mosquito. Using sugar sources to attract mosquitoes to an ingestion toxicant is a relatively simple and inexpensive, strategy that has been shown to be highly efficacious for mosquito control in a limited number of trials. Limited data suggest efficacy, even in sugar-rich environments, due to the high frequency of sugar feeding.

Early studies examined the effect of spraying ingestion toxicants on attractive flowers to use their scent as bait. While these flowers effectively attract the target mosquitoes, the impact on non-target insects, especially pollinators, can be devastating. Furthermore, this approach is not suitable where there is a lack of flowering vegetation. Subsequent studies evaluated locally available plants and fruits as attractants. While such attractants can be sprayed onto non-flowering green vegetation, further studies evaluated products (bait stations) that could be used across a wide variety of settings including indoors and in areas without suitable vegetation.

Westham Compagny recently developed a bait station that contains a plant-based mosquito attractant, sugar as a feeding stimulant, and an active ingredient (the neonicotinoid, dinotefuran) to kill the foraging vectors. The bait station has a protective membrane that covers and protects the bait from rain and dust, but that allows mosquitoes to feed through it. The Westham ATSB can remain effective in the field for at least six months and has a shelf life of greater than three years with no specific requirements for storage. This Attractive Target Sugar Bait (ATSB) is now being produced at an industrial scale, uses simple and widely available ingredients, and is environmentally friendly. The bait station was designed to have the lowest practicable material content with a high proportion of the mass being fully biodegradable. The protective membrane allows mosquitoes to feed, but it serves as a barrier to pollinators. Field studies to-date have also shown that the ATSB has a minimal impact on non-target organisms. This includes evidence specifically for the toxicant that will be used, dinotefuran. Initial environmental assessment and subsequent field trials in Mali have demonstrated that when deployed within the ATSB, the toxicant does not pose safety risks to non-target organisms, including pollinators and humans.

ATSBs may be a particularly important vector control tool in the context of insecticide resistance. Insecticide resistance for the six insecticide classes currently used in LLINs and IRS threatens malaria prevention efforts. Resistance to pyrethroids (used in LLINs and IRS) is commonly reported. If pyrethroids lose most of their efficacy, more than 55% of the benefits of vector control could be lost. ATSBs can help mitigate insecticide resistance to these contact insecticides because they can use ingestion toxicants from very different chemical classes. There are many existing ingestion toxicants that may be used in a bait station, which could facilitate resistance prevention strategies, such as rotation or combination approaches.