Five-year WHO investigation shows that LLINs remain a highly effective tool in the malaria fight
Mosquito resistance to insecticides is a growing concern. According to the World Malaria Report 2015, 60 countries have reported resistance to at least one of the four insecticide classes used in long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) since 2010; of these, 49 countries have reported resistance to two or more insecticide classes.
In 2011, WHO spearheaded a large, multi-country evaluation to assess the impact of insecticide resistance on malaria vector control interventions – primarily LLINs, the mainstay of malaria prevention. The five-year evaluation, funded by the Bill & Melinda Gates Foundation, was conducted in 340 locations across five countries: Benin, Cameroon, India, Kenya and Sudan.
The study findings were presented on 16 November in a symposium at the American Society of Tropical Medicine and Hygiene (ASTMH) meeting in Atlanta.
Researchers found that people who slept under LLINs in the evaluation areas had significantly lower rates of malaria infection than those who did not use a net, even though mosquitoes showed resistance to pyrethroids (the only insecticide class used in LLINs) in all of these areas. They attributed the continued efficacy of LLINs to the barrier provided by the nets themselves and to the fact that, even in areas where mosquitoes have developed resistance to pyrethroids, treated nets may still kill the mosquitoes.
“A resistant mosquito may not die immediately after landing on a net, but it could continue to absorb insecticide as it seeks a way to get through and bite a person beneath the net,” said Dr. Tessa Knox, a WHO scientist involved in the evaluation. “This may eventually kill the mosquito and stop onward transmission of malaria parasites,” she added.
This study reaffirms the WHO recommendation of universal LLIN coverage for all populations at risk of malaria. The findings are consistent with recent research conducted by the Centers for Disease Control and Prevention (CDC).
New tools needed
While the study findings are encouraging, WHO continues to highlight the urgent need for new and improved malaria-fighting tools to accelerate progress towards global elimination goals. WHO is calling for greater investments in vector control interventions, improved diagnostics and more effective medicines.
Active management of insecticide resistance is also of critical importance. To prevent an erosion of the impact of core vector control tools, WHO underscores the need for all countries with ongoing malaria transmission to develop and apply effective insecticide resistance management strategies. Information should be leveraged to inform timely decisions on which tools to apply where, and when.