Evaluation of new insecticides and long lasting treatments for nets and other materials used in malaria vector control and personal protection

Introduction: World Health Organisation (WHO) recommends synthetic pyrethroids for impregnation of bednets. Practical obstacles to sustainable malaria vector control measure include emergence of pyrethroid resistant mosquitoes and inadequate re-treatment of bednets. This study aims to evaluate alternative insecticides and new tools for malaria vector control and personal protection, to detect insecticide resistance mechanisms and to establish new impregnation processes on long lasting materials.

Methods: This evaluationwas carried out in experimental huts at Mabogini, Moshi, Northern Tanzania where the predominant malaria vector is Anopheles arabiensis between December 2004 and March 2005. Bednets and sheets treated with permethrin (500 mg/m2) manually and through industrial processes (long lasting treatments), were evaluated in each of the three experimental huts by a Latin square design. The construction and operation of the huts is as per earlier description by Smith (1963). Two sleepers per hut slept from 20.00 until 06.00 h and in the morning dead and alive mosquitoes were collected in paper cups. After classification by abdominal conditions malaria vector species were held for 24 h to observe mortality.

Results: The deterrent effect of permethrin (500 mg/m2) on hut entry of An. arabiensis were as higher in permethrin net and sheet, 77% and 40% than olyset net and sheet, f{49% and 2%. The increased exophily of An. arabiensis due to repellence effect of permethrin (500 mg/m2) treated sheet and net were 11% and f{3%, respectively, and slightly similar to Olyset sheet and net, 12% and f{4%, respectively. Blood feeding rate reduction for An. arabiensis were low in huts with conventionally permethrin (500 mg/m2) treated sheet than in Olyset sheet, f{10% and 13%, respectively. Mortality rates of An. arabiensis were 22% and 30% in permethrin sheet and net, 32% and 42% in Olyset sheet and net, respectively. In contrast, C. quinquefasciatus showed low deterrent effect, repellent effect and blood feeding rates than An. arabiensis and had the same mortality rates due to both conventionally treated materials and olyset net and sheet.

Interpretation: Conventionally permethrin treated materials were more effective than long lasting treatments with permethrin in terms of deterrence and repellence against An. arabiensis. Ongoing data will be presented.