Date of Award

2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Abstract

For more than a century, Rift Valley Fever (RVF) and some arboviruses such as dengue, chikungunya, and yellow fever have posed serious challenges to both public health and animal health. Nguruman region of Kajiado County recorded its first RVF case during the 1997/1998 outbreak. Despite this history, no follow-up study has been carried out to monitor virus activity. This study specifically explored the mosquito abundance and diversity virus infection rates and their host blood-feeding patterns. It also sought to assess the seroprevalence of RVFV in the human population and circulation of arboviruses within the mosquito community. Cross-sectional monitoring of adult mosquitoes using CO2 baited using BG-Sentinel traps and CDC light traps was carried out after long rains between February 2021 and May 2023 in twelve sites representing three ecological zones (conservancy, farmlands, and livestock areas) in Nguruman. Immature stages were sampled from breeding sites and reared to adulthood in a field-based laboratory. The collected mosquitoes were preserved in liquid nitrogen and transported to the Icipe in Nairobi for processing. The sources of blood meals in engorged mosquito specimens were identified by PCR. Mosquitoes were tested in pools (n = 3,045) for virus infection using cell culture in Vero cells and RT-PCR. A generalized linear mixed-effects model was used to analyze ecology and site-level effects on mosquito abundance. Human serum samples were collected from October 2020 to May 2021 from patients attending Entosopia Health Centre. Patients presenting with symptoms associated with RVF infection and consented were enrolled in the study, and a questionnaire was used to collect demographic data. Exposure to RVFV was determined using the Plaque Reduction Neutralization Test. A total of twenty-five thousand two hundred and fifty-nine mosquitoes were collected, comprising 32 species belonging to 9 genera: Mansonia (19), Anopheles (1,879), Aedes (16,260), Culex (7,088), Uranotaenia (7), Orthopodomia (1), Coquilletidia (1), Eretmapodites (3), and Toxorhynchites (1). Aedes mcintoshi (57.2%) was the most prevalent species and the sole primary vector of RVFV identified in the study area, while the secondary vectors (An. squamosus, Mn. africana, Cx. poicilipes, Mn. uniformis, Ae. Sudanensis, Cx. pipiens, and Cx. univittatus) that mainly spread the virus during outbreaks constituted 28.2%. Although no virus was isolated from the mosquito population, blood meal analysis revealed that both primary and secondary vectors displayed opportunistic feeding behavior, with blood meals from wild birds, livestock, humans, non-human primates, and wildlife. RVF seroprevalence of 7.8% (95% CI: 4.50 – 13.03) was recorded, with age (p=0.0034) and occupation (p=0.0012) showing a significant association with RVFV seropositivity. The presence of potential RVFV mosquito vectors with distinct ecological niches and broad host feeding behavior highlights the complexity of potential RVFV transmission cycles in the area. The serological evidence in humans underscores the need for a One-health approach to improve inter-epidemic surveillance of RVF for risk mapping and outbreak prediction

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