Wash resistance and efficacy of three long‐lasting insecticidal nets assessed from bioassays on Anopheles culicifacies and Anopheles stephensi

Abstract

Summaryobjective To test the wash resistance and efficacy of long-lasting insecticidal nets (LLINs), namely Olyset Ò Net and PermaNet Ò 2.0; and a long-lasting treatment kit, K-O Tab Ò 1-2-3, on Anopheles culicifacies and An. stephensi, major malaria vectors in India, by bioassays. Conventionally treated deltamethrin net (CTDN with K-O Tab) was used for comparison.method Mortality and median time for knockdown (MTKD) of mosquitoes were determined using contact bioassays and ball frame bioassays respectively. Hand washing and machine washing were used.results LLINs showed good bio-efficacy against An. culicifacies and An. stephensi. The mortality of mosquitoes remained >80% after up to 20 hand washes and up to 15 machine washes on all LLINs tested. No significant differences were observed in mortalities between the An. culicifacies and An. stephensi in cone bioassays (P > 0.05). MTKD increased progressively with successive washes and there was a significant difference in median time for knockdown of test mosquitoes and between hand-washed and machine-washed nets (P < 0.05).conclusion LLINs are more efficacious and last longer when washed by hand than by machine.

Comparison of the efficacy of long-lasting insecticidal nets PermaNet® 2.0 and Olyset® against Anopheles albimanus under laboratory conditions

“…These results allow us to evaluate wash resistance in this LLIN and showed that the regeneration time persisted for 15 washes without losing efficacy, although this decreased somewhat by 20 washes. This is slightly different than results from several other studies, in which the efficacy of PermaNet ® 2.0 was maintained even after 20 washes under laboratory and field conditions against some of the most important disease vectors around the world (Kroeger et al 2004, Graham et al 2005, Sreehari et al 2009, Atieli et al 2010). This could be due to differences in insecticide susceptibility or landing behaviour of the CIDIEM An.…”

“…Olyset ® nets are known to have a slow recovery bioefficacy under laboratory conditions, although a facilitation of its biological activity is expected by heating at 60ºC (Hougard et al 2000). These results prompted the manufacturer to recommend exposing the net to direct sunlight to recover its efficacy faster; this accelerated diffusion due to heat exposure was also confirmed by Gimnig et al (2005) and Sreehari et al (2009). However, the knowledge that direct sunlight is harmful to pyrethroid-based insecticides, because ultraviolet rays break down pyrethroid molecules rendering the insecticide ineffective, prompted the WHO to recommend placing Olyset ® in sealed polythene bags before leaving them for a few hours in the sun after washing (WHO 2003).…”

“…The efficacy of this net has also been shown to be very high even when undergoing different types of washing. Sreehari et al (2009) observed increased efficacy of PermaNet ® in producing > 80% mortality in Anopheles culicifacies and Anopheles stephensi mosquitoes after up to 20 hand washes and up to 10 machine washes. Atieli et al (2010) concluded that PermaNet ® 2.0 retained its efficacy longer with successive washes using three different washing methods (machine, hand and washing on rocks) compared to the three other brands of LLINs evaluated.…”

Entomological evaluation of PermaNet 2.0®and K-O Tab 1-2-3®treated nets in comparison to nets conventionally treated with deltamethrin, after repeated washing

“…Sreehari et al compared wash resistance of PN2 and KO 123 treated nets up to 20 hand and machine washes. 15 Their method of hand washing differs from the authors' method in the present study. There was no significant difference between PN2 and KO 123 treated nets with respect to %mortality and KD time after 20 washes which is confirmed by the authors' study.…”

Community Coverage with Insecticide-Treated Mosquito Nets and Observed Associations with All-Cause Child Mortality and Malaria Parasite Infections

“…Net age is an area for future work. Evidence suggests that the insecticide in LLINs maintains its efficacy up to 3 years 29,30 or 20 washes 31 ; however, holes in nets may decrease their effectiveness, 32 and future research should verify that LLINs maintain their effectiveness for preventing both malaria infection and child mortality over time.…”