Better bed nets for malaria: the need for a long-term solution

News article 17 Jul 2013
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In an interview with Public Radio International’s The World programme, LSTM Director, Professor Janet Hemingway, talks about her ongoing concerns over the dependence on bed nets all treated with the same class of insecticides. This follows the praise of many world leaders in 2008 on the mass distribution of bed nets to reduce malaria deaths. However, this short-term solution has failed to address a long-term problem that is insecticide resistance.

“A number of us were worried that it was too simplistic a story right at the beginning,” says Professor Hemingway. The hundreds of millions of nets distributed across Africa in recent years were all treated with the same class of insecticides, called pyrethroids. The bed nets used in people’s homes are impregnated with the insecticide that kills the mosquitoes. A number of experts, including Professor Hemingway, predicted that pyrethriod treated nets would not provide a long-term solution, with mosquitoes evolving and becoming resistant to the pesticide, which may reduce the effectiveness of the nets. Resistance is then likely to emerge more quickly if you blanket an area with bed nets that all contain the same insecticide. “People almost didn’t believe that resistance was going to be an issue,” Professor Hemingway recalls. “I for one had been going around for many years saying, ‘you’re going to get this problem.’”

The prediction has turned out to be correct. Research conducted at Malawi’s Malaria Alert Centre, has shown that as many as 80% of mosquitoes survive pyrethroid exposure.  The treated nets themselves were also found to be less durable than promised, tearing too easily, reducing protection. This echoes the findings of other studies including research overseen by Professor Hemingway, who says “Distributing nets into pyrethroid-resistant areas, where those nets are going to develop holes quite quickly, is going to give you very little protection.”

Insecticide treated nets are an excellent tool for preventing malaria if we get the right products. As well as creating more durable bed nets, the alternative approach would have been to use two classes of insecticide instead of one. This would have increased the life-span of the nets and allowed scientists more time to develop new insecticides for future use. However, at the time only one class of insecticide was approved for use and so Professor Hemingway and others malaria experts, supported the universal bed net campaign and the short-term benefit it would bring, while pushing for the support for the development of new insecticides, saying:   “The last thing any of us want is to find that we’ve got a catastrophic failure of these nets, and suddenly all the gains that we’ve got in terms of reducing malaria transmission are being lost,” she says, “because you will see that in terms of young children dying.”

The World Health Organization (WHO) predicts that if the insecticides on bed nets continue to fail, an additional 120,000 African children will die from malaria each year. Research into the development of new insecticides continues at LSTM’s Department of Vector Biology, in the Innovative Vector Control Consortium hosted by LSTM and in other organisations, however there will probably not be a new insecticide ready for another four or five years.

 

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