The effect of the spatial repellent metofluthrin on landing rates of outdoor biting anophelines in Cambodia, S.E. Asia

Without controlling outdoor transmission, the goal of elimination of malaria is unlikely to be reached. This is particularly the case in places like Cambodia where people spend considerable amounts of time away from houses at night. Metofluthrin is a synthetic pyrethroid insecticide with a high vapor action at ambient temperatures and has been developed as a long lasting insect repellent device that works without the need to apply heat. Emanators of 10% of metofluthrin were therefore tested in landing collections against potential malaria vectors from three areas of the country (Pailin, Pursat and Koh Kong). One to four emanators were hung on wire 1m off the ground on one or four sides of a square 1.5m from collectors. Collections were also undertaken with Furvela tent-traps. 2086 hrs of landing collection were undertaken in Pailin, 528hrs in Veal Veng and 320 in Kroh Salau. Rate ratios were used to determine the significance of the difference between collections. The principal anophelines collected varied between locations. Anopheles minimus s.l. was the most common mosquito in Pailin, An. maculatus s.l in Veal Veng and An. sinensis in Kroh Salau. Among all species collected in Pailin landing rates were reduced by 50% (95% CI 55-44%) when a single emanator was used and by 58% (95% CI 63- 52%) when four were used. The effect was greater in An.minimus s.l 51% ( 95% CI 54-47%) and 70% (72%-66%) respectively. A similar result was obtained in Pursat, where 67% (95% CI 66- 42%) reductions were observed when four emanators were in use, but no significant reduction was observed in Koh Kong. Although the results show promise it is argued that the product needs further development.