Efficacy of Long-lasting Insecticidal Nets With Declining Physical and Chemical Integrity on Aedes aegypti (Diptera: Culicidae)

Abstract

Fitting long-lasting insecticidal nets (LLIN) as screens on doors/windows has a significant impact on indoor-adult Aedes aegypti (L.), with entomological reductions measured in a previous study being significant for up to 2 yr post-installation, even in the presence of pyrethroid-resistant Aedes populations. To better understand the mode of LLIN protection, bioassays were performed to evaluate the effects of field deployment (0, 6, and 12 mo) and damage type (none, central, lateral, and multiple) on LLIN efficacy. Contact bioassays confirmed that LLIN residual activity (median knockdown time, in minutes, or MKDT) decreased significantly over time: 6.95 (95% confidence interval [CI]: 5.32–8.58) to 9.24 (95% CI: 8.69–9.79) MKDT at 0- and 12-mo age, respectively, using a pyrethroid-susceptible Aedes strain. Tunnel tests (exposing human forearm for 40 min as attractant) showed that deployment time affected negatively Aedes passage inhibition from 54.9% (95% CI: 43.5–66.2) at 0 mo to 35.7% (95% CI: 16.3–55.1) at 12 mo and blood-feeding inhibition from 65.2% (95% CI: 54.2–76.2) to 48.9% (95% CI: 26.4–71.3), respectively; both the passage/blood-feeding inhibition increased by a factor of 1.8–2.9 on LLINs with multiple and central damages compared with nets with lateral damage. Mosquito mortality was 74.6% (95% CI: 65.3–83.9) at 0 mo, 72.3% (95% CI: 64.1–80.5) at 6 mo, and 59% (95% CI: 46.7–71.3) at 12 mo. Despite the LLIN physical integrity could be compromised over time, we demonstrate that the remaining chemical effect after field conditions would still contribute to killing/repelling mosquitoes.

Temporal Evaluation of Insecticide Resistance in Populations of the Major Arboviral Vector Aedes Aegypti from Northern Nigeria

“…Previous studies have encouraged the use of insecticide treated materials, such as the LLINs for control of diurnally active Ae. aegypti [64,65]. In the course of our Anopheles collection in Kano, we have found on several occasions some blood fed Aedes mosquitoes resting indoors.…”

Insecticide-treated house screening protects against Zika-infected Aedes aegypti in Merida, Mexico

“…Previous studies from our research team have characterized the susceptibility/resistance levels of Ae. aegypti from Juan Pablo II (JP), with knockdown resistance (allele frequency of I1016 of 82% and C1534 of 93%) to pyrethroids [16,18]. Mosquito populations from JP are from moderately resistant to completely susceptible to alpha-cypermethrin, the active ingredient of the LLIN material used for the ITS intervention evaluated in this study.…”

“…Mosquito populations from JP are from moderately resistant to completely susceptible to alpha-cypermethrin, the active ingredient of the LLIN material used for the ITS intervention evaluated in this study. The insecticidal activity of ITS has shown to be effective (>70% mortality) as a chemical barrier, in addition to the benefits of house screening as a physical barrier [16,18], to exclude and kill mosquitoes and eventually protect against mosquito bites, which is epidemiologically relevant if most transmission occurs indoors.…”

“…The integration of HS and Long-lasting insecticidal nets (LLIN), known as insecticidetreated screening (ITS) [15], can provide simple, safe, and low-tech Aedes control. Projects supported by TDR/IDRC within the "Eco-Bio-social Research" and "Ecohealth" programmes in Mexico showed that LLIN affixed as ITS on doors and windows act as a physical/chemical barrier [16] and confer sustained protection for indoor-female Aedes aegypti [17][18][19]. Cluster randomised controlled trials in two endemic localities for Ae.…”

Effects of piperonyl butoxide synergism and cuticular thickening on the contact irritancy response of field Aedes aegypti (Diptera: Culicidae) to deltamethrin

“…Because mosquitoes typically rest indoors after a blood meal to facilitate the diuresis process, 1,2 a growing body of research supports the efficacy of IRS and the use of LLINs in reducing the population of A. aegypti (Linnaeus) mosquitoes and preventing the transmission of dengue fever. [3][4][5][6][7][8] Insecticide resistance is the main challenge in efforts to control dengue fever. Two major mechanisms of pyrethroid resistance are detoxification through the overexpression of metabolic enzymes and mutation at targeted sites of the sodium channel.…”