London School of Hygiene & Tropical Medicine

A mosquito net that stops female mosquitoes from producing fertile eggs has the potential to improve malaria control efforts in areas of high insecticide resistance, according to a new study published in Science Translational Medicine. The research was led by the London School of Hygiene & Tropical Medicine and tested Olyset® Duo, a new type of net produced by Sumitomo Chemical Co.

Using a long-lasting insecticide treated net (LLIN) that kills the Anopheline mosquitoes which transmit malaria is the simplest and most effective way to prevent the disease. The World Health Organization estimates that over half the population of sub-Saharan Africa now sleep under LLIN and this, together with improved diagnosis and treatment, has reduced malaria cases by a third and mortality rates by two-thirds over the last 15 years.

However, pyrethroids are currently the only class of insecticide used on LLIN and the rapid spread of resistance to these insecticides in malarial mosquitoes threatens further progress unless new types of nets can be developed.

The Olyset Duo net is treated with a mixture of insecticides: a standard pyrethroid and a novel insecticide pyriproxifen that disrupts the maturation of eggs in the ovaries of mosquitoes which come into contact with the net. The scientists evaluated the capacity of the Olyset Duo net to control pyrethroid-resistant mosquitoes in laboratory tests and small-scale field trials under household conditions in West Africa.

They found that the Olyset Duo net killed more pyrethroid-resistant malarial mosquitoes than the standard pyrethroid net and sterilised those mosquitoes which remained alive after exposure to the net. By preventing mosquito reproduction, the new net has the potential to reduce mosquito populations and restore control of malaria transmission in areas of high pyrethroid resistance. After 20 rigorous washes the Olyset Duo LLIN was still active in household trials.

Dr Corine Ngufor from the London School of Hygiene & Tropical Medicine, the scientist leading the trial in Benin, West Africa, said: "Identifying novel types of insecticide which can be incorporated into the fibre of the net is no easy task. It then takes years of collaboration with chemical industry to establish a formulation that can withstand regular washing of the net and still kill or sterilise the mosquitoes under field conditions. This product is showing great promise".

Professor Mark Rowland, the Project Coordinator at the School said: "Sumitomo are leading the way on the development of the next generation of long-lasting insecticide treated nets that will control pyrethroid resistant mosquitoes, just as they did with the first ever LLIN, Olyset Net, developed 20 years ago."

"Insecticide treated nets are the most important tool we have in the fight against malaria, and it's encouraging to see new technology which in the future could continue to prevent malaria transmission in vulnerable communities."

The development and evaluation of Olyset Duo is the result of partnership between the manufacturer Sumitomo Chemical Co. of Japan, the London School of Hygiene & Tropical Medicine, and the Innovative Vector Control Consortium - the organisation funded by the Bill and Melinda Gates Foundation to support the development of new vector control tools to control pyrethroid resistant mosquitoes.

Olyset Duo has now entered community randomised trials in Burkina Faso, led by Durham University, to confirm whether the net will prevent malaria transmission better than standard long-lasting pyrethroid treated nets.

Publication

• Corine Ngufor, Raphael N'Guessan, Josias Fagbohoun, Damien Todjinou, Abibath Odjo, David Malone, Hanafy Ismail, Martin Akogbeto, Mark Rowland, Efficacy of the Olyset Duo net against insecticide-resistant mosquito vectors of malaria, Science Translational Medicine, DOI: 10.1126/scitranslmed.aad3270

Related links

• Paving the way to a malaria-free world - feature
• Malaria Centre

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