Transmission of Plasmodium falciparum malaria parasites occurs when nocturnal Anopheles mosquito vectors feed on human blood. In Africa, where malaria burden is greatest, bednets treated with pyrethroid insecticide were highly effective in preventing mosquito bites and reducing transmission, and essential to achieving unprecedented reductions in malaria until 2015 1. Since then, progress has stalled 2 and with insecticidal bednets losing efficacy against pyrethroid-resistant Anopheles vectors 3,4 , methods that restore performance are urgently needed to eliminate any risk of malaria returning to the levels seen prior to their widespread use throughout sub-Saharan Africa 5. Here we show that the primary malaria vector Anopheles gambiae is targeted and killed by small insecticidal net barriers positioned above a standard bednet, in a spatial region of high mosquito activity but zero contact with sleepers, opening the way for deploying many more insecticides on bednets than currently possible. Tested against wild pyrethroid-resistant Anopheles gambiae in Burkina Faso, pyrethroid bednets with organophosphate barriers achieved significantly higher killing rates than bednets alone. Treated barriers on untreated bednets were equally effective, without significant loss of personal protection. Mathematical modelling of transmission dynamics predicted reductions in clinical malaria incidence with barrier bednets that matched those of 'next-generation' nets recommended by WHO against resistant vectors. Mathematical
Advances in digitized video-tracking and behavioral analysis have enabled accurate recording and quantification of mosquito flight and host-seeking behaviors, enabling development of Individual (agent) Based Models at much finer spatial scales than previously possible. We used such quantified behavioral parameters to create a novel virtual testing model, capable of accurately simulating indoor flight behavior by a virtual population of host-seeking mosquitoes as it interacts with and responds to simulated stimuli from a human-occupied bed net. We describe the model, including base mosquito behavior, state transitions, environmental representation and host stimulus representation. In the absence of a bed net and human bait, flight distribution of the model population is relatively uniform in the arena. Introducing an unbaited net induces a change in distribution due to landing events on the net surface, predominantly occurring on the sides and edges of the net. Presence of simulated human baited net strongly impacted flight distribution patterns, exploratory foraging, the number and distribution of net landing sites, depending on the bait orientation. As recorded in live mosquito experiments, contact with baited nets (a measure of exposure to the lethal insecticide) occurred predominantly on the top surface of the net. Number of net contacts and height of contacts decreased with increasing attractant dispersal noise. Results generated by the model are an accurate representation of actual mosquito behavior recorded at and around a human-occupied bed net in untreated and insecticide treated nets. In addition to providing insights into host-seeking behavior of endophilic vectors, this fine-grained model is highly flexible and has significant potential for in silico screening of novel bed net designs, accelerating the deployment of new and more effective tools for protecting against malaria in sub-Saharan Africa.
Background Advances in digitized video-tracking and behavioural analysis have enabled accurate recording and quantification of mosquito flight and host-seeking behaviours, facilitating development of individual (agent) based models at much finer spatial scales than previously possible. Methods Quantified behavioural parameters were used to create a novel virtual testing model, capable of accurately simulating indoor flight behaviour by a virtual population of host-seeking mosquitoes as they interact with and respond to simulated stimuli from a human-occupied bed net. The model is described, including base mosquito behaviour, state transitions, environmental representation and host stimulus representation. Results In the absence of a bed net and human host bait, flight distribution of the model population was relatively uniform throughout the arena. Introducing an unbaited untreated bed net induced a change in distribution with an increase in landing events on the net surface, predominantly on the sides of the net. Adding the presence of a simulated human bait dramatically impacted flight distribution patterns, exploratory foraging and, the number and distribution of landing positions on the net, which were determined largely by the orientation of the human within. The model replicates experimental results with free-flying living mosquitoes at human-occupied bed nets, where contact occurs predominantly on the top surface of the net. This accuracy is important as it quantifies exposure to the lethal insecticide residues that may be unique to the net roof (or theoretically any other surface). Number of net contacts and height of contacts decreased with increasing attractant dispersal noise. Conclusions Results generated by the model are an accurate representation of actual mosquito behaviour recorded at and around a human-occupied bed net in untreated and insecticide-treated nets. This fine-grained model is highly flexible and has significant potential for in silico screening of novel bed net designs, potentially reducing time and cost and accelerating the deployment of new and more effective tools for protecting against malaria in sub-Saharan Africa.
Barrier bednets (BBnets), regular bednets with a vertical insecticidal panel to target mosquitoes above the bednet roof, where activity is highest, have the potential to improve existing Insecticidal Treated Bednets (ITNs), by reducing quantity of insecticide required per net, reducing the toxic risks to those using the net, thus increasing the range of insecticides to choose from. We evaluated performance of different BBnet variants based on the PermaNet 3 (i.e., P3 BBnets with pyrethroid and piperonyl butoxide (PBO) on the roof or barrier; pyrethroid alone on the side walls) in room-scale bioassays, simultaneously video- recorded to track mosquitoes. Experimental results showed the longitudinal P3 barrier (P3L) to be highly effective: P3+P3L were consistently though not significantly more effective than the reference P3 bednet while performance of Ut+P3L was comparable to the reference P3. Comparing contact duration at the treated sections of each variant, the Ut+P3L accumulated 1273 contacts with 1374 seconds duration, all on the barrier, greatly exceeding the 792 seconds duration, from 8049 contacts, accumulated across the entire surface of the PermaNet 3 reference bednet. The BBnets potential to augment existing bednets and enhance their performance is considered.
Many mosquito vectors rest inside human habitations, a behavioral trait that is exploited for vector control by indoor residual spraying (IRS) of interior walls with insecticide. Although IRS and its refined version targeted IRS are very effective against Aedes aegypti, they are expensive and logistically challenging to deliver in densely populated urban areas where outbreaks of dengue and other arboviruses are the greatest challenge. In experiments in Recife, Brazil, we set out to quantify the indoor resting behavior of Ae. aegypti at a level beyond that previously reported. We found that significantly more Ae. aegypti males, unfed and fed females visited the base of walls (height 0–20 cm, corresponding to 12.3% of the total wall surface) more frequently than upper wall areas, with the difference more pronounced at higher temperatures. When the lowest 20 cm of the walls was treated with an appropriate insecticide and colored black, we recorded up to 85% cumulative mortality after 24-h exposure in the experimental room. The findings are significant because feasibly, householders could treat this small and accessible target zone manually, without the need for visits by costly IRS teams or equipment, reducing insecticide use and enabling communities to actively protect their own indoor environment.
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