Long-lasting insecticidal nets retain bio-efficacy after 5 years of storage: implications for malaria control programmes

Musa, Jeremiah J; Moore, Sarah J; Moore, Jason; Mbuba, Emmanuel; Mbeyela, Edgar; Kobe, Dickson; Swai, Johnson K; Odufuwa, Olukayode G; (2020) Long-lasting insecticidal nets retain bio-efficacy after 5 years of storage: implications for malaria control programmes. Malaria Journal, 19 (1). DOI: https://doi.org/10.1186/s12936-020-03183-y

Abstract

<jats:title>Abstract</jats:title><jats:sec> <jats:title>Background</jats:title> <jats:p>Long-lasting insecticidal nets (LLINs) are the most sustainable and effective malaria control tool currently available. Global targets are for 80% of the population living in malaria endemic areas to have access to (own) and use a LLIN. However, current access to LLINs in endemic areas is 56% due to system inefficiencies and budget limitations. Thus, cost-effective approaches to maximize access to effective LLINs in endemic areas are required. This study evaluated whether LLINs that had been stored for 5 years under manufacturer’s recommended conditions may be optimally effective against <jats:italic>Anopheles</jats:italic> mosquitoes, to inform malaria control programmes and governments on the periods over which LLINs may be stored between distributions, in an effort to maximize use of available LLINs.</jats:p> </jats:sec><jats:sec> <jats:title>Methods</jats:title> <jats:p>Standard World Health Organization (WHO) bioassays (cone and tunnel test) were used to evaluate the bio-efficacy and wash resistance of Olyset<jats:sup>®</jats:sup> and DawaPlus<jats:sup>®</jats:sup> 2.0 (rebranded Tsara<jats:sup>®</jats:sup> Soft) LLINs after 5 years of storage at 25 °C to 33.4 °C and 40% to 100% relative humidity. In addition, a small scale Ifakara Ambient Chamber test (I-ACT) was conducted to compare the bio-efficacy of one long stored LLINs to one new LLIN of the same brand, washed or unwashed. LLINs were evaluated using laboratory reared fully susceptible <jats:italic>Anopheles gambiae</jats:italic> sensu stricto (s.s.) (Ifakara strain) and pyrethroid resistant <jats:italic>Anopheles arabiensis</jats:italic> (Kingani strain).</jats:p> </jats:sec><jats:sec> <jats:title>Results</jats:title> <jats:p>After 5 years of storage, both unwashed and washed, Olyset<jats:sup>®</jats:sup> and DawaPlus<jats:sup>®</jats:sup> 2.0 (Tsara<jats:sup>®</jats:sup> Soft) LLINs passed WHO bio-efficacy criteria on knockdown (KD60) ≥ 95%, 24-h mortality ≥ 80% and ≥ 90% blood-feeding inhibition in WHO assays against susceptible <jats:italic>An. gambiae</jats:italic> s.s. DawaPlus<jats:sup>®</jats:sup> 2.0 LLINs also passed combined WHO bioassay criteria against resistant <jats:italic>An. arabiensis.</jats:italic> Confirmatory I-ACT tests using whole nets demonstrated that long-stored LLINs showed higher efficacy than new LLINs on both feeding inhibition and mortality endpoints against resistant strains.</jats:p> </jats:sec><jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Even after long-term storage of around 5 years, both Olyset<jats:sup>®</jats:sup> and DawaPlus<jats:sup>®</jats:sup> 2.0 LLINs remain efficacious against susceptible <jats:italic>Anopheles</jats:italic> mosquitoes at optimal storage range of 25 °C to 33.4 °C for temperature and 40% to 100% relative humidity measured by standard WHO methods. DawaPlus<jats:sup>®</jats:sup> 2.0 (Tsara<jats:sup>®</jats:sup> Soft) remained efficacious against resistant strain.</jats:p> </jats:sec>