Pyrethroid Resistance Intensity of Anopheles gambiae sensu lato (Diptera: Culicidae) from Phase II Hut Trial Station in KOLOKOPE, Eastern Plateau Togo: A Potential Site to Assess the Next Generation of Long- Lasting Insecticidal Nets

Per WHO recommendations, the implementation of the next-generation of Long Lasting Insecticidal Nets (LLINs) for malaria vector control requires appropriate investigations on the insecticide resistance profile of the vector and the impact of the LLINs on the known resistant mosquitoes. The next-generation of LLINs are actually an incorporation of a mixture of pyrethroid insecticides and a synergist such as PBO. Several studies have proven the additional impact of PBO on the increase in the mortality rate of Anopheles gambiae s.l. (Diptera: Culicidae). However, further assessments need to be done at community level in order to set a stage for the acceleration of the WHO policies on the implementation of the next-generation of LLINs. Kolokope is a cotton-growing area in the central region of Togo characterized by an intensive use of agro pesticides and insecticides. A phase II experimental hut station for the evaluation of mosquito control tools has been built in Kolokope. For the characterization of the site, WHO susceptibility tests using diagnostic doses of eight insecticides, PBO synergist assay and intensity assay of three pyrethroids (5x and 10x) were conducted on adult female mosquitoes obtained from larvae collected around the site. Anopheles gambiae s.l. from Kolokope showed high resistance to pyrethroids and DDT, but in lesser extent to carbamates and organophosphates. Likewise, high intensity of resistance to pyrethroid was observed with less than 40% mortality at 10x deltamethrin, 52 and 29% mortality at 10x permethrin and 10x alphacypermethrin, respectively. Also, the addition of PBO showed a reversal mortality which was similar to mortality rate at 10x doses of pyrethroids. The high pyrethroid intensity resistance recorded at Kolokope could be mainly due to the pressure on An. gambiae s.l. through the excessive use of insecticide in agriculture. This can be used for the assessment of the next-generation of LLINs either in experimental hut or at a community trial.