Village trial of bednets impregnated with wash-resistant permethrin compared with other pyrethroid formulations.
A village-scale field trial of pyrethroid-impregnated mosquito nets was undertaken in The Gambia, West Africa, in the Mandinka village of Saruja (13 degrees 13'N, 14 degrees 55'W) during July-November 1989. Nearly all the villagers possessed and used their own bednets. Anopheles gambiae is the main vector of human malaria in the area. An experimental wash-resistant formulation of permethrin was compared with standard emulsifiable concentrate (EC) formulations of permethrin and lambda-cyhalothrin, versus placebo-treated bednets. Target concentrations of pyrethroids on bednets were permethrin 500 mg/m2 and lambda-cyhalothrin 25 mg/m2. The experimental design involved random allocation of a treatment to one net per family. Whereas 68% of people questioned said they washed their nets fortnightly, observations during the 16-week trial period showed that only 4/130 (3%) of nets involved in the trial had been washed as frequently as once per month. Early morning searches for mosquitoes under bednets (1 day/week for 16 weeks) found significantly more mosquitoes (60% An.gambiae) in placebo-treated nets than in pyrethroid-treated nets. The numbers found with each of the three pyrethroid treatments did not differ significantly from each other. Insecticidal efficacy of the treatments was tested by bioassays using wild-caught unfed mosquitoes exposed to netting for 3 min. Linear regression analysis of bioassay mortality against number of times that a net had been washed by villagers showed that nets impregnated with the wash-resistant permethrin retained their insecticidal properties better than nets impregnated with lambda-cyhalothrin or with the standard permethrin formulation.
Miller
J E
JE
Department of Medical Parasitology, London School of Hygiene and Tropical Medicine, U.K.
Lindsay
S W
SW
Armstrong Schellenberg
J R
JR
Adiamah
J
J
Jawara
M
M
Curtis
C F
CF
D000818:Animals; D000852:Anopheles; D001512:Bedding and Linens; D001681:Biological Assay; D005260:Female; D005714:Gambia; D007306:Insecticides; D009032:Mosquito Control / Q000379:methods*; D009570:Nitriles; D026023:Permethrin; D010573:Pesticide Residues; D011722:Pyrethrins / Q000008:administration & dosage; D011795:Surveys and Questionnaires
D007306:Insecticides; D009570:Nitriles; D010573:Pesticide Residues; D011722:Pyrethrins; D026023:Permethrin; C037304:cyhalothrin