Comparison of house spraying and insecticide-treated nets for malaria control

The efficacies of using residual house spraying and insecticide-treated net s against malaria vectors are compared, using data from six recent comparis ons in Africa, Asia and Melanesia. By all the entomological and malariologi cal criteria recorded, pyrethroid-treated nets were at least as efficacious as house spraying with dichlorodiphenyltrichloroethane (DDT), malathion or a pyrethroid. However, when data from carefully monitored house spraying p rojects carried out between the 1950s and 1970s at Pare-Taveta and Zanzibar (United Republic of Tanzania), Kisumu (Kenya) and Garki (Nigeria) are comp ared with recent insecticide-treated net trials with apparently similar vec tor populations, the results with the insecticide-treated nets were much le ss impressive. Possible explanations include the longer duration of most of the earlier spraying projects and the use of non-irritant insecticides. No n-irritant insecticides may yield higher mosquito mortalities than pyrethro ids, which tend to make insects leave the site of treatment (i.e. are excit o-repellent). Comparative tests with non-irritant insecticides, including t heir use on nets, are advocated. The relative costs and sustainability of s praying and of insecticide-treated net operations are briefly reviewed for villages in endemic and epidemic situations and in camps for displaced popu lations. The importance of high population coverage is emphasized, and the advantages of providing treatment free of charge, rather than charging indi viduals, are pointed out.