Mosquito nets infused with two pesticides work much better against malaria than those with only one, reducing prevalence in children by 44 percent, according to a recent study.
As a result of the report, published in The Lancet last month, the World Health Organization has recommended that the two-chemical nets be used in areas where mosquitoes have developed resistance to the first-line insecticide.
The new nets contain pyrethroids, a class of chemicals used in nets for over a decade, along with the newer compound, piperonyl butoxide, which blocks mosquitoes’ ability to break down pyrethroids. (It is sometimes called a “pesticide synergist.”)
The Vestergaard company, which introduced pyrethroid-infused nets in 2004, later developed a two-chemical version that the W.H.O. began evaluating in 2014. Now many companies have similar nets awaiting W.H.O. approval.
It is hard to find new insecticides suitable for nets, because they must kill or repel mosquitoes and yet be safe for the babies and youngsters who sleep under them. The insecticides also must be able to stand up to washing and intense sunlight.
Piperonyl butoxide largely fades away after two years. In the study’s second year, protection by nets with piperonyl butoxide had diminished, and malaria prevalence in children was reduced by only 33 percent.
Insecticide-impregnated nets are considered an important factor in the world’s recent success against the disease: malaria deaths dropped 60 percent between 2000 and 2015.
Other factors included coating walls inside homes with long-lasting pesticides, prophylactic treatment of pregnant women and young children during malaria seasons, new rapid malaria tests and treatment using compounds based artemisinin, which comes from wormwood plants.
Large cash infusions also helped. The George W. Bush administration made a major commitment, launching the President’s Malaria Initiative in 2005 and contributing a third of the budget of the Global Fund to Fight AIDS, Tuberculosis and Malaria.
Recently, however, the distribution of millions of free nets in Africa has become a contentious issue because so many are misused. Fishermen use them for catching or drying fish, and small farmers fence their gardens with them.
On April 25, World Malaria Day, Uganda’s health minister threatened to have police arrest citizens using nets distributed by her government for any purpose other than fighting malaria.