Entomological indicators of malaria transmission and insecticide resistance profile of Anopheles gambiae at the early phase of irrigated rice farming in the forest area of central Cameroon

Abstract

Background: Cameroonian authorities have recently established irrigated rice projects across the country. The assessment of the impact of such projects in the transmission of vector-borne diseases, such as malaria, imposes to compare the situation before and after their implementation in a given locality. In Bankeng, a village in a forest area in Cameroon, no preliminary data on malaria transmission indicators was collected before the implantation of irrigated rice farming. To attempt to catch up for this shortcoming 6 months after the first rice seedlings were sown., the present study aimed to generate data which could serve as a baseline to assess the impact of irrigated rice farming in Bankeng. Methods : A cross-sectional study was performed at the end of the rainy season in July 2018. Mosquitoes were sampled by night collections on human volunteers, identified morphologically and members of different complexes further sorted to species using molecular tools. Plasmodium infectious status was determined by Taqman genotyping. To assess resistance profile to insecticides, WHO bioassays were performed using two-to-five days old females An. gambiae s.l. reared from larval collections in Bankeng. Furthermore, the molecular basis of resistance were investigated Results : An. gambiae s.l represented 98% of the 1087 mosquitoes collected with Anopheles gambiae as the predominant species. The total human biting rate was 44.5 bites/person/night. Entomological inoculation rate was 3.8 ib/p/n. The Bankeng An. gambiae population exhibited a high level of resistance to almost all insecticides except to organophosphates with a high frequency of L1014F kdr mutation (93.9%) and a 6-fold over-expression of CYP6P3 P450 gene.  Conclusion : In the absence of preliminary data before the implementation of the irrigated rice fields; the present study provides interesting data which could help for the future assessment of the impact of irrigated rice cultivation on malaria transmission in the locality of Bankeng.