ROLE OF ENTOMOLOGICAL FACTORS IN SUSTENANCE OF RESIDUAL MALARIA PARASITE TRANSMISSION IN KILIFI COUNTY, KENYAN COAST

Abstract

Malaria vector control strategies have been rolled out in malaria endemic areas leading to reduction in disease transmission and morbidity in some regions. However, the persistence in local malaria transmission has not been fully comprehended. The current study assessed the entomological factors sustaining residual malaria transmission in selected loci in Kilifi County along the Kenyan coast. Adult mosquito vectors were collected indoor and outdoor stations from six (6) selected villages in Kilifi using CDC light traps and Human Landing Catches (HLC). All the Anopheles mosquitoes collected were morphologically identified and then tested for sporozoite infection and blood meal sources using ELISA. Phenotypic insecticide susceptibility testing was done using standard WHO test kit. Sibling species of An. gambiae s.l. were separated by PCR. A total of 415 Anopheles mosquitoes were collected; 57 % outdoors and 43 % indoors in the 6 villages. Majority was collected by HLC (76.4 %) compared to LT catches (23.4 %). Anopheles funestus s.l. was the dominant species (75 %) followed by An. arabiensis (16 %), An. gambiae s.s. (4 %) and An. pretoriensis (1 %). Plasmodium falciparum circumsporozoite protein test showed an overall sporozoite infectivity rate of 2.65 %. The total overall indoor annual entomological inoculation rate for the study area (Kilifi) was estimated to be 62.05ib/p/year. Insecticide susceptibility level to Permethrin was 96 % (0.92-0.99, 95 % C.I) and Deltamethrin - 94 % (0.89-0.99, 95 % C.I). Malaria transmission in the study area is maintained by modestly zoophagic vectors An. funestus s.l. and An. arabiensis mostly happened outdoors. This study has shown evidence of resistance to the common pyrethroids used in LLINs by the phenotypic insecticide assessment done. This validates the need to expand monitoring for insecticide resistance and implementation of an insecticide resistance management strategy to sustain the gains made in malaria control