Effect of insecticide-treated bed nets on house-entry by malaria mosquitoes: The flight response recorded in a semi-field study in Kenya

Abstract

Insecticide-treated nets are currently a major tool to reduce malaria transmission. Their level of repellency affects contact of the mosquito with the net, but may also influence the mosquito's entry into the house. The response of host-seeking malaria mosquitoes approaching the eave of an experimental house was recorded within a large screen house. We compared entry- and exit rates in relation to the presence in the house of different insecticide-treated bed nets (ITNs) with an untreated net. Mosquitoes were lured towards the house by dispensing a synthetic host-odour blend from within the net in the house. Complementary WHO bioassays revealed that the treated nets caused high knock-down- and mortality responses to the Anopheles gambiae sensu stricto strain tested. The proportion of mosquitoes that came into view of the cameras and subsequently entered the house did not differ between treated nets and the untreated net. Treated nets did not affect proportions of mosquitoes that exited the house and departed from view around the eave. However, the percentage of house-leaving and re-entering mosquitoes when an insecticide- treated net was present, was lower than in the presence of an untreated net. Our results indicated that there was no spatial repellent effect from pyrethroid-treated nets that influences house-entry at eave level. It is argued that the toxic effect of treated bed nets resulted in a reduced number of mosquitoes re-entering the house, which could thereby affect malaria transmission in neighbouring, unprotected houses.

Host-seeking activity of a Tanzanian population of Anopheles arabiensis at an insecticide treated bed net

“…No volatile or pre-contact repellent effects of the LLINs had been observed in either study, suggesting that observed behaviours were responses by mosquitoes after LLIN contact. This is supported by a recent report that LLINs did not affect house entry rates [66]. A limitation of our study was that the closed test room design prevented the detection of exiting behaviour following net contact.…”

Protective effects of Olyset® Net on Plasmodium falciparum infection after three years of distribution in western Kenya

“…Mosquitoes exposed to permethrin will not seek a blood meal even under these conditions because of a loss of the ability to sense host cues. Similarly, the deterrence will be beneficial for persons who are not under an LLIN [56,57]. Further, this effect may reduce early-hour biting activity in the room or even outdoor biting activity near a house with an Olyset ® [8].…”

Dynamic modelling of personal protection control strategies for vector-borne disease limits the role of diversity amplification

“…One method for reducing mosquito contacts with humans is to disrupt the mosquito -host interaction with the use of bed nets. Because CO 2 , volatile skin chemicals, heat and moisture plumes readily pass through net meshing, bed nets interfere with neither the initial long-range search phase nor the identification and approach portion of the second short-range phase (spatial repellency effects of insecticide-treated nets are observed to be weak or non-existent) [36,37]. Bed nets do, however, interfere with the landing portion of short-range phase by physically blocking mosquitoes from reaching landing sites, thus preventing biting and the transition to the final gonotrophic phase.…”

“…Bed nets do, however, interfere with the landing portion of short-range phase by physically blocking mosquitoes from reaching landing sites, thus preventing biting and the transition to the final gonotrophic phase. Mosquito enter/ exit rates at net-occupied dwellings [37] suggest that there is a limit to the amount of time that mosquitoes will attempt to gain access to net-protected human hosts, after which they will abandon the effort and leave to find blood elsewhere.…”