Effectiveness of permanet® dual on malaria vector control in a Pyrethroid resistant population of mosquitoes in western Kenya

Abstract

Malaria affected 263 million people and resulted to 597000 deaths globally. In Kenya 5.5 million malaria cases were reported in 2023. Malaria cases and deaths globally have decreased through long-lasting insecticide treated nets (LLINs) and indoor residual spraying (IRS). However, intensive use of these strategies has led to a rise in resistance, which necessitated development and trials of new generation LLINs (nLLINs). New generation LLINs are products impregnated with a pyrethroid and another insecticide to enhance their efficacy against pyrethroid resistant malaria transmitting mosquitoes. However, there are gaps in knowledge regarding effectiveness of nLLINs on vectors resistant to pyrethroids. Specific objectives of the work were to evaluate phenotypic resistance on malaria vectors between nLLINs and pyrethroid only nets; to determine the difference in blood feeding inhibition (BFI) of malaria vectors between nLLINs and untreated nets, and to determine the difference in mortality of malaria vectors between nLLINs and untreated nets in western Kenya. This was an experimental huts study with seven arms, where each study hut was weekly allocated different treatments of the nLLINs, namely permanet 3.0 (PN 3.0), permanet dual (PD), interceptor G2 (IG2), as unwashed and after 20X washes, together with an untreated Polyester net (UN X0). The huts were randomly allocated sleepers daily. Mosquito samples were collected from the huts every morning from 6:30 AM to 8:30 AM, to aid in efficacy assessment of the study treatments against wild malaria vectors. Data analysis for phenotypic resistance was calculated as mortality proportions and analyzed using Fisher’s exact test. Data on blood feeding inhibition and mortality were analyzed utilizing ANOVA and Tukey (HSD) test. The study detected phenotypic resistance of 66.7% with An. gambiae and 88.9% with An. funestus, against pyrethroids as well as significant association between phenotypic resistance and net types among mosquito species; An. gambiae X2 =7.1875, p – value 0.03; An. funestus X2 = 11.875, p = 0.003. ANOVA test for BFI and mortality produced p-values of 0.000 and 0.001<0.05 respectively. Significant differences in blood feeding inhibition were noted between UN X0 vs PD 20X , PN 3.0 0X, PN 3.0 20X, IG2 20X, all with adjusted p. values of less than 0.05. PN 3.0 0X vs IG2 0X and PD 0X (adjusted p. values <0.05) and PN 3.0 20X vs IG2 0X and PD 0X (all with p values <0.05). On mortality, UN 0X vs IG2 20X, PD 0X and PD 20X, with adjusted p-values of 0.008, 0.005 and 0.002, respectively, which were statistically significant. Overall, the study confirmed existence of significantly different phenotypic resistance between nLLINs relative to the conventional interventions, thus affirming the importance of nLLINs as probable substitutes in the fight against pyrethroid resistance. PN3.0 was found to be the better product based on its significantly better BFI performance. PD proved to be the best product on mosquito mortality and was the promising intervention for future consideration in that regard. Altogether, PD was found to be effective against the An. funestus mosquitoes, due to its outstanding mortality results. There is need for continuous monitoring of insecticide resistance situation in regions facing pyrethroid resistance to keep abreast and properly manage the resistance from an informed opinion. Altogether, use of nLLINs is an effective intervention against insecticide resistance.