New research has suggested that mosquitoes are able to develop resistance to insecticide-coated bed nets.

The researchers, based in Senegal, found that the number of mosquitoes that were resistant to the insecticide deltamethrin had reached 37%. Their findings were published in The Lancet Infectious Diseases journal.

The researchers also suggest the nets reduced the immunity of older children and adults to malaria infection.

The use of bed nets is the cheapest and most effective way of preventing malaria in developing countries; however, other experts say the study was too small to draw conclusions about the long-term effectiveness of nets.

Over the last few years the nets have been widely distributed in Africa and elsewhere – the World Health Organization says that when properly deployed they can cut malaria rates by half.

The scientists were led by Dr Jean-Francois Trape from the Institut de Recherche pour le Developpement in Senegal. The authors are worried that their study has implications beyond Senegal.

Dr Joseph Keating from Tulane University, New Orleans, US, acknowledges the concerns the study raises.

“If indeed this is a real trend we are seeing in this part of Senegal then it has very important implications for future malaria prevention and control strategies.”

However, he goes on to say, “I would certainly advise extending the study a couple of more years which would be helpful in determining if this is a true trend or is it something specific to that particular area.

“We need to be very careful when generalising these data to the larger continent of Africa as a whole; there is plenty of variation between communities and within communities.”

The Lancet Infectious Diseases