Deltamethrin treated bednets for control of malaria transmitted by Anopheles culicifacies (Diptera : Culicidae) in India

In a malaria endemic area in Orissa state in eastern India baseline (Novemb er 1989 to October 1990) malaria incidence ranged from 215 to 328 cases/1,0 00 population/yr in different groups of villages. In November 1990, nylon b ednets treated with deltamethrin at 25 mg/m(2) were given out in two villag es (population 1062), untreated bednets were given out in five villages (po pulation 1,226) and in one village (population 786) nets were not given. Ne ts were retreated in October 1991 and June 1992 in treated-net villages. Th e trial continued until October 1992. The treated nets caused significant r eduction in indoor resting density, biting (landing), light trap catches, h uman engorgement rate, and parous rate of malaria vector Anopheles culicifa cies Giles as compared with untreated nets or no nets. Untreated nets also caused reductions in biting and indoor density. Treated nets retained insec ticidal action well over 6 mo. In the final year, malaria incidence was red uced 8.9% in the no-net village, 34.9% in the villages with untreated nets, and 59.1% in villages with treated nets. The relative risk of malaria and parasite rates declined significantly in villages with treated nets. Pediat ric splenomegaly rate did not change in the no-net village, increased signi ficantly in villages with untreated nets, but decreased significantly in th ose with treated nets. Treated nets also reduced pediatric anemia rates, bu t Hb concentration increased in all villages. Considering the benefits of t reated bednets and development of resistance among vectors to DDT and malat hion, bednets treated with deltamethrin could be an effective alternative s trategy to control malaria in forested areas in India.