Residual Effects of Permethrin Impregnated Bed Nets

The objective of this field trial was to assess the residual effectiveness of permethrin 10% treated mosquito nets on malaria control compared with untreated nets. The study was carried out between July and December 2007 in the Pong Nam Ron District of Chantaburi Province, Thailand. Mosquito population densities were assessed using the landing catch method. Mosquitoes were collected between 6:00 PM and 12:00 PM. Residual effectiveness of the treated nets was assessed using standard WHO bioassay tests carried out monthly using Anopheles dirus mosquitoes reared in the insectary of the Department of Medical Entomology, Faculty of Tropical Medicine, Mahidol University, Thailand. The results showed the population densities of Anopheles spp, including the malaria vector Anopheles minimus, were unaffected in the study area where mosquito nets treated with Mossmann 100 (permethrin 10% EC) at 300 mg/m2 were used. WHO bioassay tests showed the nets treated with Mossmann 100 remained biologically effective against An. dirus for up to six months. Indigenous cases of malaria were reduced by 27.7% at the site where the nets treated with Mossman 100 (permethrin 10% EC) were used but no changes in malaria cases at the control site were seen. and Lines (1985) compared the efficacy of different insecticides available for this purpose. Mosquito nets treated with pyrethroid insecticides have been shown to protect users from malaria (Cheng et al, 1995; JanaKara et al, 1995; Nevill et al, 1996; Curtis et al, 1998). The widespread distribution of insecticide-impregnated bed nets is a major component of the WHO global strategy for malaria control, especially in sub-Sahara Africa where more than 90% of malaria cases are reported annually. In Thailand DDT applied as an indoor residual spray was the original major measure for malaria vector control programs. Introduced in 1949 DDT was replaced after INTRODUCTION Malaria is a serious problem in many tropical and subtropical countries. Indoor residual sprays are used in endemic areas to control disease vectors but effective alternatives are essential for successful management of malaria. Darriet et al (1984) reported the successful use of pyrethroid-treated mosquito nets for malaria control and Curtis SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 230 Vol 40 No. 2 March 2009 four decades by organophosphate and pyrethroid insecticides. Additional control measures using insecticide treated nets were introduced and pyrethroid treated nets have now been used in malaria control programs since 1992. The present study was carried out to assess the residual effectiveness for malaria control using mosquito nets treated with Mossmann 100 (permethrin 10% EC) compared to untreated nets. MATERIALS AND METHODS