Large-scale spraying of bednets to control mosquito vectors and malaria in Sichuan, China

Since 1987, up to 2.42 million bednets owned by rural householders in over 40 counties in seven prefectures of Sichuan Province, China, have been sprayed annually with deltamethrin at a dose of about 10 mg/m2. Data for the years 1987-89 indicate that there were marked reductions in the biting populations and survival of the two vector species Anopheles anthropophagus and A. sinensis. Extensive tests in 1992 in areas where bednet spraying had been carried out for 5 years showed that mortality was 100% with the WHO-recommended discriminating dose of deltamethrin, i.e., there was no indication of resistance. Malaria data obtained by passive surveillance of reported cases, mass blood surveys of schoolchildren, and active surveillance of reported blood slides from fever cases all indicated marked reductions after introduction of the net spraying. In contrast, in the control areas, where the nets were not treated, the situation remained static or deteriorated slightly.