Current observations on shifts in malaria vector biting behavior and changing vulnerability to malaria transmission in contrasting ecosystems in Western Kenya.

Designing, implementing, and upscaling effective malaria vector control strategies necessitates understanding of when and where transmission occurs. This study assessed the biting patterns of potentially infectious malaria vectors at various hours, locations, and human behavior in different ecological settings in western Kenya. Hourly indoor and outdoor catches of human-biting mosquitoes were sampled from 1900 to 0700 hours for four consecutive nights in four houses per village using human landing collection method. The nocturnal biting activities of each species were expressed as the mean number of mosquitoes landing per person per hour. The human behavior study was conducted via observations and questionnaire surveys. Species within and complexes were differentiated by polymerase chain reaction (PCR) and the presence of circumsporozoite proteins (CSP) determined by enzyme-linked immunosorbent assay (ELISA). Altogether, a total of 2,037 adult female Anophelines were collected comprising of A (76.7%), (22.8%) and (0.5%). Overall, was the predominant species collected in Ahero (96.7%) while was dominant in Kisian (86.6%) and Kimaeti (100%) collections. PCR results revealed that constituted 80.5% and 79% of the samples analysed from Ahero and Kisian respectively. (hereafter )(98.1%) was the dominant species collected in Kimaeti. All the samples analysed belonged to ( hereafter ). Indoor biting densities of and exceeded the outdoor biting densities in all sites. The peak biting occurred early morning between 0430-0630 hours in the lowlands for both indoors and outdoors. In the highlands (Kimaeti), the peak biting of occurred between 0100-0200 hours indoors. Over 50% of the study population stayed outdoors from 1800 to 2200 hours and woke up at 0500 hours coinciding with the times highest numbers of vectors were collected. The sporozoite rate was higher in vectors collected outdoors, with being the main malaria vector in the lowlands and in the highland. The study shows heterogeneity of Anophelines distribution, high outdoor malaria transmission, and peak biting activity by (early morning ) when humans are not protected by bed nets in the lowland sites. Additional vector control efforts targeting the behaviors of these vectors i.e using non-pyrethroids-based indoor residual spraying and spatial repellents outdoors are needed.