Durability monitoring of long-lasting insecticidal (mosquito) nets (LLINs) in Madagascar: physical integrity and insecticidal activity

Abstract

BackgroundLong-lasting insecticidal mosquito nets (LLINs) are highly effective for malaria prevention. However, it is also clear that durability monitoring is essential to predict when, post-distribution, a net population, no longer meets minimum WHO standards and needs to be replaced. Following a national distribution campaign in 2013, we tracked two durability indicators, physical integrity and bio-efficacy at six and 12 months post-distribution. While the loss of net integrity during this period was in line with expectations for a one-year net life, bio-efficacy results suggested that nets were losing insecticidal effect faster than expected. The rate of bio-efficacy loss varied significantly between different net brands.MethodsWe tested 600 randomly selected LLINs, 200 from each of three net brands. Each brand came from different eco-epidemiological zones reflecting the original distribution scheme. Fabric integrity (size and number of holes) was quantified using the proportional hole index (pHI). A subsample of the nets, 134 new nets, 150 at six months and 124 at 12 months, were then tested for bio-efficacy using the World Health Organization (WHO) recommended method.ResultsThree net types, Netprotect®, Royalsentry® and Yorkool®, were followed. After six months, 54%, 39% and 45%, respectively, showed visible loss of integrity. The median pHI by type was estimated to be one, zero and one respectively. The percentage of damaged nets increased after 12 months such that 83.5%, 74% and 68.5%, had holes. The median pHI for each brand of nets was 47.5, 47 and 23. No significant difference in the estimated pHI at either six or 12 months was observed. There was a statistically significant difference in the proportion of hole size category between the three brands (χ 2 = 15.761, df = 4, P = 0.003). In cone bio-assays, mortality of new Yorkool® nets was surprisingly low (48.6%), mortality was 90.2% and 91.3% for Netprotect® and Royalsentry® (F (2, 131) = 81.59, P < 0.0001), respectively. At 12 month use, all tested nets were below the WHO threshold for replacement.ConclusionThese findings suggest that there is a need for better net quality control before distribution. More frequent replacement of LLINs is probably not an option programmatically. Regardless of prior approval, LLIN durability monitoring for quality assessment as well as net loss following distribution is necessary to improve malaria control efforts.Electronic supplementary materialThe online version of this article (10.1186/s13071-017-2419-7) contains supplementary material, which is available to authorized users.

Physical integrity of three Long-Lasting Insecticidal Net products 30 months after a mass-distribution campaign in Benin

“…The categorization of these pHI according to the WHO standards [20] as being in "good condition", "damaged but usable" or "to replace" showed us that after 30 months of use, 29.5 % of the LLINs (all brands) were in good condition. This result was higher than those observed in Madagascar in 2012 [21] where the proportion of LLINs to be replaced after 30 months was 16.9%. Dura polyethylene LLINs have had the highest proportion of LLINs in "to be replace" category (34.1%) after 30 months of follow-up in our study.…”

Spatio-temporal mapping of Madagascar’s Malaria Indicator Survey results to assess Plasmodium falciparum endemicity trends between 2011 and 2016

“…This temporal heterogeneity may be partly attributable to reductions in NMCP activities caused by Global Fund disbursement delays in 2014 [ 40 ]. In addition, recent evidence of the variable quality and durability of the insecticide-treated bed-net brands distributed across the country means that over their 3-year lifespans (mass distribution campaigns in Madagascar are triennial), protection from nets will be inconsistent [ 42 ]. MIS campaigns in Madagascar have all been timed to take place in the transmission season following mass bed-net distribution campaigns, which may, therefore, capture snapshots of prevalence at its lowest.…”

Monitoring the durability of the Long-Lasting Insecticidal Nets MAGNet and Royal Sentry in three ecological zones of Mozambique

“…However, the majority of LLINs were still minimally effective at 36 months, even as chemical content ranged from 32-81% of target dose. This compares favourably to Madagascar, where mosquito mortality for Royal Sentry fell from 90% at baseline to 23% at 12 months, but with signi cant variation between sites [21]. Phase 2 trials in India indicated that MAGNet retained 100% mortality in cone bioassays after 25 washes [22], and in Burkina Faso washing MAGNet 20 times resulted in a 40% reduction in protection against pyrethroid-resistant Anopheles gambiae sensu lato blood feeding [23].…”