Assessment of the Durability and Bio-effectiveness of Three Long-Lasting Insecticidal Nets in Three Different Communities After the 2017 Mass Net Distribution Campaign in Benin

Abstract

Long-lasting insecticidal nets (LLINs) are an essential tool in the fight against malaria. Physical integrity, durability and bio-effectiveness are key variables in the effectiveness of LLINs. The objective of this study was to identify the main factors affecting the survival of three brands of LLINs with different physical characteristics and to assess their bio-effectiveness. A cohort consisting of 1500 LLINs (500 of each) of the brands: DawaPlus®2.0 (polyester, 150 denier, 40 g/m2 fabric weight), PermaNet®2.0 and Yorkool® (polyester, 75 denier, alternating knit pattern with 85 g/m2 fabric weight) was monitored every 6 months in the communes of Ketou, Dogbo and Djougou (from October 2017 to September 2019) based on attrition and integrity measures and median survival in years. We also determined bio-efficacy using the WHO cone test. The physical presence rate was 26.4%, 21.4% and 48.6% respectively for DawaPlus®2.0, PermaNet®2.0 and Yorkool®. The main cause of loss of the three LLINs was displacement, 43.6% (in rural areas) versus 43.2% (in urban areas) with no significant difference (p ˃ 0.05). The median proportional hole index (pHI) ranged from 578 (IQR: 219-843) at 6 months to 196 (IQR: 46-524.5). After 24 months of use, 86.1% were in good condition (0≤pHI<65), 9% were damaged (65≤pHI<643) and 4.2% were too torn (643≤pHI). A significant decrease in physical survival of LLINs (all brands) was observed at 24 months (37.9%, range 34.7-41.3%) compared to 6 months (90.3%, range 88.7-91.8%) (p<0.001). The 24-hour mortality of the three LLINs met WHO requirements for efficacy. The decline in LLIN survival rates during this study highlights the need to develop and implement new strategies to manage this important vector control tool.