Abstract
Royal Guard is a new insecticide-treated bed-net incorporated with a mixture of alpha-cypermethrin and pyriproxyfen (an insect growth regulator). We assessed its efficacy and wash-resistance in laboratory and experimental hut studies following WHO guidelines. Mosquitoes that survived exposure to the net were kept in separate oviposition chambers and observed for the reproductive effects of pyriproxyfen. In laboratory assays, Royal Guard induced > 80% mortality and > 90% blood-feeding inhibition of An. gambiae sl mosquitoes before and after 20 standardised washes and sterilised blood-fed mosquitoes which remained alive after exposure to the net. In an experimental hut trial against wild free-flying pyrethroid-resistant An. gambiae sl in Cové Benin, Royal Guard through the pyrethroid component induced comparable levels of mortality and blood-feeding inhibition to a standard pyrethroid-only treated net before and after 20 washes and sterilised large proportions of surviving blood-fed female mosquitoes through the pyriproxyfen component; Royal Guard induced 83% reduction in oviposition and 95% reduction in offspring before washing and 25% reduction in oviposition and 50% reduction in offspring after 20 washes. Royal Guard has the potential to improve malaria vector control and provide better community protection against clinical malaria in pyrethroid-resistant areas compared to standard pyrethroid-only LLINs.
Highlights
Vector control is a major pillar in the control and prevention of malaria
Nets treated with a combination of pyrethroids and the synergist PBO have recently received conditional endorsement from World Health Organisation (WHO) based on evidence from a cluster randomised trial in northern Tanzania demonstrating additional public health value of one type of pyrethroid-PBO net (Olyset Plus) compared to a pyrethroid-only long-lasting insecticidal nets (LLINs) product in an area with a moderate intensity of pyrethroid resistance partly conferred by monooxygenase-based resistance m echanism[8,9]
Royal Guard is a 120 dernier net made from a proprietary blend of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) treated with a mixture of alpha-cypermethrin and pyriproxyfen, both incorporated into the monofilament yarn during the extrusion process
Summary
Vector control is a major pillar in the control and prevention of malaria. It relies primarily on two core interventions; long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS)[1]. LLINs are easier to deliver and highly cost-effective, providing both community protection[2,3] and personal protection to the user They are the most widely used public health intervention for malaria prevention and control and have contributed significantly to the remarkable reductions in malaria burden observed in endemic countries in the last two decades[4]. PyrethroidPBO LLINs are expected in theory to have an increased killing effect on malaria mosquitoes that express mixedfunction oxidase based pyrethroid resistance mechanisms that are inhibited by the PBO in the net. They are unlikely to be effective everywhere as some vector populations have developed complex and multiple resistance mechanisms that may not be affected by the synergistic action of P BO8,10. Effective vector control and management of pyrethroid resistance in malaria vectors cannot rely on pyrethroid-PBO nets alone; other innovative and effective classes of LLINs treated with non-pyrethroids urgently need to be developed to increase the toolbox available to vector control programmes
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