Outdoor residual spray for the control of monkey malaria vectors in Sarawak, Malaysia

The increase in cases of monkey malaria in humans, especially in Malaysia Borneo which is believed to be due to infection by the malaria vector that took place outdoor, shows the importance of outdoor residual spraying in controlling this vector. This study aims to evaluate the effectiveness of the new formulation deltamethrin K-Othrine® (PolyZone) and examine its suitability in the control of knowlesi malaria vector in Sarawak, in comparison to deltamethrin K-Othrine® WG250 wettable granule, the insecticide currently use in the vector control programme. The study was performed at three sites in Sarawak having similar type of houses made out of wood and concrete. Houses of two sites were sprayed outdoor with deltamethrin K-Othrine® (PolyZone) at two different dosages, one site with 25 mg/m2 and the other site with 30 mg/m2. Houses of the third site (control house) were sprayed indoor with deltamethrin K-Othrine® WG 250 wettable granule at 25 mg/m2. Residual activity on different walls was assessed using WHO standard cone bioassay techniques. For vector surveillances, larvae and adult surveillance were conducted pre and post spraying. Nested and semi-nested PCR was conducted to detect the malaria parasite in adult mosquitoes. Outdoor residual sprayed of Deltamethrin K-Othrine® (PolyZone) presented higher efficacy compared to indoor residual sprayed of Deltamethrin K-Othrine® WG 250. The efficacy of different type of wall surfaces (wood and concrete) was found varied. Deltamethrin K-Othrine® (PolyZone) at 30 mg/m2 was the most effective with regards to ability to cause higher mortality. Spraying activity conducted during this study, has resulted in malaria cases in Julau reduced significantly. Based on findings of this study, it is recommended to consider outdoor residual spraying on wall surfaces in the community for improved effectiveness of malaria vector control programme.