Insecticide For Mosquito Nets

Insecticide-treated bed nets (ITNs) are a form of personal protection that has been shown to reduce malaria illness, severe disease, and death due to malaria in endemic regions. In community-wide trials in several African settings, ITNs were shown to reduce the death of children under 5 years from all causes by about 20%.

How Do ITNs Work?

Bed nets form a protective barrier around people sleeping under them. However, bed nets treated with an insecticide are much more protective than untreated nets.

The insecticides that are used for treating bed nets kill mosquitoes, as well as other insects. The insecticides also repel mosquitoes, reducing the number that enter the house and attempt to feed on people inside. In addition, if high community coverage is achieved, the numbers of mosquitoes, as well as their length of life will be reduced. When this happens, all members of the community are protected, regardless of whether or not they are using a bed net. To achieve such effects, more than half of the people in a community must use an ITN.

Net Materials and Insecticides

Nets may vary by size, shape, color, material, and/or insecticide treatment status. Most nets are made of polyester, polyethylene, or polypropylene.

Only two insecticides classes are approved for use on ITNs (pyrroles and pyrethroids). These insecticides have been shown to pose very low health risks to humans and other mammals, but are toxic to insects and kill them. Previously, nets had to be retreated every 6 to 12 months, or even more frequently if the nets were washed. Nets were retreated by simply dipping them in a mixture of water and insecticide and allowing them to dry in a shady place. The need for frequent retreatment was a major barrier to widespread use of ITNs in endemic countries. In addition, the additional cost of the insecticide and the lack of understanding its importance resulted in very low retreatment rates in most African countries.

Recent studies have suggested that the rise of pyrethroid resistance may undermine the effectiveness of nets. To help manage resistance, some net products incorporate piperonyl butoxide (PBO) along with a pyrethroid insecticide, but there is not yet evidence that this significantly improves ITN effectiveness in areas with high levels of pyrethroid resistance, and WHO currently does not consider nets that incorporate PBO to be tools for managing pyrethroid resistance.

Several companies have developed long-lasting insecticide-treated nets (LLINs) that maintain effective levels of insecticide for at least 3 years, even after repeated washing. The WHO Pesticide Evaluation SchemeExternal (WHOPES) has given either full or interim approval to more than 15 of these LLINsCdc-pdfExternal for use in the prevention of malaria. CDC is currently testing some of these and other LLINs to assess their performance and durability in the field.