A COMPARISON OF USE OF A PYRETHROID EITHER FOR HOUSE SPRAYING OR FOR BEDNET TREATMENT AGAINST MALARIA VECTORS

In an intensely malarious area in north-east Tanzania, microencapsulat ed lambdacyhalothrin was used in four villages for treatment of bednet s (provided free of charge) and in another four villages the same inse cticide was used for house spraying. Another four villages received ne ither intervention until the end of the trial but were monitored as co ntrols. Bioassays showed prolonged persistence of the insecticidal res idues. Light traps and ELISA testing showed reduction of the malaria. vector populations and the sporozoite rates, leading to a reduction of about 90% in the entomological inoculation rate as a result of each t reatment. Collections of blood fed mosquitoes showed no diversion from biting humans to biting animals. Incidence of re-infection was measur ed by weekly monitoring of cohorts of 60 children per village, after c learing preexisting infection with chlorproguanil-dapsone. The vector control was associated with a reduction in probability of re-infection per child per week by 54-62%, with no significant difference between the two vector control methods. Cross-sectional surveys for fever, par asitaemia, haemoglobin and weight showed association of high parasitae mia with fever and anaemia and beneficial effects of each intervention in reducing anaemia. However, passive surveillance by resident health assistants showed no evidence for reduced prevalence of fever or para sitaemia. Net treatment consumed only about one sixth as much insectic ide as house spraying and it was concluded that the former interventio n would work our cheaper and nets were actively demanded by the villag ers, whereas spraying was only passively assented to.