Long-Term Insecticidal Activity and Physical Integrity of Olyset Nets in Tafea Province, Vanuatu

Abstract

The long-term efficacy of long-lasting insecticidal nets (LLINs) depends on both the physical condition of the net and the residual activity of the insecticide. This study focused on monitoring these parameters in Olyset nets (Sumitomo Chemical Co., Osaka, Japan) (n = 101) that had been used for 1-3 yr in Tafea Province, Vanuatu. Net usage and frequency of washing was ascertained by questionnaire; the nets were assessed with regards to cleanliness and damage owing to holes. Insecticide efficacy was determined with cone bioassays using Anophelesfarauti Laveran. Net usage was high and 86.1% (87 of 101) of villages stated that they used the net every night. Washing of nets was low (11.9%, 12 of 101), and most nets (79.2%, 80 of 101) were considered dirty. Most nets were damaged (73.4% had holes), and 22.8% (23 of 101) had large holes (>200 cm2). The 24-h mortality of An. farauti exposed to nets aged 1-2 yr was 79.4%, while the mortality for nets 3 yr of age was significantly lower at 73.7%. There was no difference in the insecticidal activity of clean compared with dirty nets (mean 24-h mortality: Clean = 76.7%, Dirty = 77.1%). Although the majority of nets had holes, the physical condition of 8.9-22.8% of nets was altered so severely to potentially affect efficacy. Although the 3-yr-old nets would still be providing significant levels of insecticidal and personal protection, consideration should be given to replacing nets >3 yr old.

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

“…At 12 months, average percent mortality was 11%, 14% and 23% for Netprotect®, Yorkool® and Royalsentry®, respectively. However, other studies in another country showed that at 12 months, the average percent of mortality could be relatively high depending on net type [ 21 , 24 , 25 ]. A significant difference of percent mortality between two localities after six months may be explained by user behavior.…”

Comparing the new Ifakara Ambient Chamber Test with WHO cone and tunnel tests for bioefficacy and non-inferiority testing of insecticide-treated nets

“…National malaria control programmes (NMCPs) must ensure that all people living in malaria transmission areas are protected through the provision, nightly use and timely replacement of high quality long-lasting insecticidal nets (ITNs) and where appropriate, the additional application of indoor residual spraying (IRS) [1]. While it is assumed that all ITNs that have World Health Organization (WHO) prequalification listing last for 3 years, several ITN products are available that may vary in price as well as performance under local conditions [1–7]. Because ITNs are the primary means of malaria control, their durability, measured through physical integrity and bioefficacy against anopheline mosquitoes, needs to be accurately assessed in order to inform NMCPs of the most cost effective products and the correct interval for net replenishment campaigns [8].…”

Culminating anti-malaria efforts at long lasting insecticidal net?

“…Moreover, in Vanuatu, although the nets were claimed to last for five years, the efficacy declined after three years of use under programmatic conditions. The insecticidal efficacy obtained for three-year-old nets was 80%, which indicated an increased risk of getting infective mosquito bites and also increased anopheline exposure to sub-lethal dosages of insecticide [36].…”