In malaria endemic countries prevention is an important part of malaria control and is achieved through:
- vector control
- personal protection measures such as insecticide-treated bed nets
- preventive treatment with antimalarial drugs of vulnerable groups such as pregnant women, who receive intermittent preventive treatment (IPT).
Insecticide-treated bed nets (ITNs)
Insecticide treated bed nets are the principal strategy for malaria prevention in areas of malaria transmission and are adopted by all countries in sub-Saharan Africa, the majority of Asian malaria-endemic countries and some Latin American countries as a key malaria control strategy.
Untreated bed nets form a protective barrier around persons using them. However, mosquitoes can feed on people through the nets, and nets with even a few small holes provide little, if any, protection. The application of a residual insecticide greatly enhances the protective efficacy of bed nets. The insecticides used for treatment kill mosquitoes and other insects. The insecticides also have repellent properties that reduce the number of mosquitoes that enter the house and attempt to feed. In addition, if high community coverage is achieved, the numbers and longevity of mosquitoes will be reduced. When this happens, all members of the community are protected, regardless of bed net ownership. To achieve such effects, high community coverage is required. Properly used these nets can reduce malaria transmission by 90% and malaria-related deaths among children and adults by one-fifth.
Previously, nets had to be retreated at intervals of 6-12 months, more frequently if the nets were washed. The need for frequent retreatment was a major barrier to full implementation of ITNs in endemic countries. The additional cost of the insecticide and the lack of understanding of its importance resulted in very low retreatment rates in most African countries. More recently, several companies have developed long-lasting insecticide-treated nets (LLINs) that retain lethal concentrations of insecticide for at least 3 years. Although long-lasting insecticidal nets are more expensive than conventional ones, the cost of maintaining coverage is lower, since they have to be retreated less frequently.
Indoor residual spraying (IRS)
The main purpose of indoor residual spraying is to reduce transmission by reducing the survival of malaria vectors entering houses or sleeping units.
Indoor residual spraying remains a valuable intervention in malaria control when the following conditions are met:
- high percentage of the structures in an operational area have adequate sprayable surfaces, and can be expected to be well sprayed;
- majority of the vector population is endophilic, i.e. rests indoors;
- vector is susceptible to the insecticide in use;
- spraying is regularly and completely (coverage of all sprayable surfaces) done
There are currently 12 insecticides recommended for IRS, including Dichloro-diphenyl-trichloroethane (DDT), which is the one with the longest residual efficacy when sprayed on walls and ceilings (6–12 months depending on dosage and nature of sub¬strate). However, the usage of DDT is contentious, hence it accumulates in the environment through food chains and in tissues of exposed organisms, including people living in treated houses. This has given rise to concern in relation to possible long-term toxicity. Growing vector resistances and the lack of development of new insecticide compounds are building major barriers to effective vector control through IRS. In the light of this research and development of new cost-effective insecticides remains crucial.