Blood Feeding Pattern of Malaria Vector Reveals Malaria Transmission Dynamics in Three Islands of Lake Victoria in Kenya

Abstract

The Lake Victoria region of western Kenya is malaria endemic with a suitable environment throughout the year for the transmission of Plasmodium parasites by its primary mosquito vector, Anopheles gambiae sensu lato (s.l.), as well as other secondary vectors. Malaria control largely depends on vector control using long-lasting insecticidal nets (LLINs) that protect humans from infectious bites while sleeping. However, the success of this strategy is greatly threatened by resistance to insecticides and changes in mosquito feeding pattern that alter disease transmission dynamics. Therefore, adequate knowledge of mosquito feeding patterns and population structure can inform the efficacy of and allow appropriate deployment of appropriate vector control strategies. In this study, mosquito feeding behaviour, Plasmodium infection, and genetic structure of malaria mosquitoes were sought to determine transmission dynamics in three malaria endemic islands of Lake Victoria in Western Kenya namely Mageta, Magare, and Ngodhe. Adult mosquitoes were trapped both indoors and outdoors of 3,081 geo-referenced buildings inhabited by about 7,221 people. Demographics and LLINs usage were also surveyed. The collected mosquitoes were morphologically identified on site and later to species level by PCR product sequencing. Sources of blood-meals in vectors were determined by high resolution melting (HRM) analysis of cytochrome b (cyt b), 16S ribosomal RNA, and cytochrome oxidase 1 (COI) genes. Malaria parasites in mosquito’s salivary glands were identified by PCR-HRM of cyt b and population structure of mosquito vector species characterized using microsatellites. The data show that the islands have an overall LLINs coverage of about 67%, while the abundance of A. gambiae sensu strictu (s.s.), Anopheles arabiensis, Anopheles funestus s.s., and Anopheles coustani remain high, enabling high malaria transmission throughout the year. Humans were the most prominent blood-meal hosts of malaria vectors in all study islands, but blood-meal hosts also included diverse non–human sources (n=9) such as cow, chicken, goat, and rat among others. Some mosquitoes (3.61%) had fed on humans in addition to cow, goat or chicken. Overall 9.86% (n=41) of engorged malaria mosquitoes, including A. coustani, harboured malaria parasites. The presence of abundant malaria mosquitoes that harbour Plasmodium falciparum and secondary blood-meal sources potentially promote malaria transmission through provision of alternative means for mosquito survival, potentially limiting the effectiveness of LLINs.