Durability of the deltamethrin-treated polypropylene long-lasting net LifeNet® in a pyrethroid resistance area in south western Benin: A phase III trial

Abstract

Background: Long-lasting insecticidal bed nets (LLINs) are a key measure for preventing malaria and their evaluation is coordinated by the World Health Organization Pesticide Evaluation Scheme (WHOPES). LifeNet® was granted WHOPES time-limited interim recommendation in 2011 after successful Phase I and Phase II evaluations. Here, we evaluated the durability and community acceptance of LifeNet® in a Phase III trial from June 2014 to June 2017 in Benin rural area.

Methods: A prospective longitudinal, cluster-randomized, controlled trial with households as the unit of observation was designed to assess the performance of LifeNet® over a three-year period, using a WHOPES fully recommended LLIN (PermaNet® 2.0) as a positive control. The primary outcomes were the bioassay performance using WHO cone assays and tunnel tests, the insecticide content and physical integrity.

Results: At baseline, 100% of LLINs were within the tolerance limits of their target deltamethrin concentrations. By 36 months only 17.3% of LifeNet® and 8.5% of PermaNet® LLINs still were within their target deltamethrin concentrations. Despite these low rates, 100% of both LLINs meet WHO efficacy criteria (≥ 80% mortality or ≥ 95% knockdown or tunnel test criteria of ≥ 80% mortality or ≥ 90% blood-feeding inhibition) after 36 months using WHO cone bio-assays and tunnel tests. The proportion of LLINs in good physical condition was 33% for LifeNet® and 29% for PermaNet® after 36 months. After 36 M the survivorship was 21% and 26% for LifeNet® and PermaNet® respectively. Although both LLINs were well accepted by the population, complaints of side effects were significantly higher among LifeNet® users than PermaNet® ones.

Conclusion: LifeNet® LLINs did meet WHO criteria for bio-efficacy throughout the study period and were well accepted by the population. This is an important step towards getting a full WHO recommendation for use in malaria endemic countries.

Fig 1. Insecticide content (g/kg) in LifeNet and PermaNet 2.0 at 0, 12, 24 and 36 months after distribution.

Fig 2. Bio-efficacy of LifeNet and PermaNet LLINs against An. gambiae Kisumu strain.

(A) and (B) show knockdown and mortality rates using cone bio-assays, while (C) and (D) display mortality and blood feeding rates using tunnel tests. Boxes display the median value, 25th and 75th percentiles. The whiskers show the 5th/95th percentiles and the dots indicate the outliers. Dashed lines indicate threshold of WHOPES efficacy criteria.

Fig 3. Physical condition of LifeNet and PermaNet LLINs based on the proportionate hole index (pHI).

Box plot indicating median and 95% confidence interval, dashed line = threshold of good net condition (pHI ≥64).

Fig 4. Survivorship of LifeNet and PermaNet LLINs.