Development of Rapid Diagnostic Tool and Characterization of Rift Valley Fever Virus Infection in Kenya
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Date
2024-06
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Kenyatta University
Abstract
Rift Valley fever (RVF) is a high-priority zoonotic disease characterized by massive loss of livestock within a short period of its outbreak. The disease is endemic in sub-Saharan Africa and mainly spread via infected female Aedes and Culex genera of mosquitoes. This study aimed to develop a rapid diagnostic tool and spatio-temporal characterization of RVF in Kenya. During this study, a calorimetric reverse transcription loop-mediated isothermal amplification (RT-LAMP) for the detection of Rift Valley Fever Virus was developed and validated. In addition, RVF infection was characterized through generation of the current RVFV transmission risk maps of Kenya by computation of the basic reproduction number (Ro) based on temperature change, presence of vector and host, and the host recovery rate. The risk maps were validated using a serological study that was carried out on 615 blood samples collected from Siaya, Busia, and Kisumu counties in the year 2018. The RVFV IgG and IgM antibodies were screened and the results confirmed using either serum viral neutralization test and/or real time polymerase chain reaction (RT-qPCR). The novel diagnostic tool that was developed detected the presence of the virus within 30 minutes at a constant temperature of 65oC with a sensitivity of 98.36% and a specificity of 96.49%. The RVFV transmission risk maps showed the likelihood of having outbreaks in seventeen counties of Kenya. Most of these counties were from arid and semi-arid lands (ASALS) whose livelihood greatly depends on livestock. However, the possibility of the disease to occur outside ASAL areas was demonstrated by the presence of IgG and IgM antibodies in counties previously perceived as RVFV-free zones. The average seropositivity rate of RVFV IgM antibodies in the three counties was estimated to be 10.33% with Siaya county leading with 24% (95% CI (2.269-8.009) OR 4.26) followed by Busia County 7% (95% CI (0.532-1.88) OR 4.26). Kisumu County recorded Zero RVFV positivity rate. The overall seropositivity rate for RVFV IgG antibodies from the three counties was at 14% with Siaya County leading at a positivity rate of 22% (95% CI 0.805 -2.140) OR 1.31), followed by Busia 18% (95% CI 0.349 -2.867) OR 1) and Kisumu 2% (95% CI (0.032-0.265) OR 0.09). The colorimetric-RVFV-UDG-RT LAMP assay was ten-fold more sensitive compared to the RT–qPCR. This is attributed to many start points for amplification in the LAMP technology as opposed to single start point in real time polymerase chain reaction (RT–qPCR). The RVF spatio-temporal model correctly predicted regions and months that the disease is likely to occur. The presence of undetected circulation of RVFV IgG and IgM antibodies in Siaya, Busia, and Kisumu counties, points to a possible impending future outbreak of the disease in these areas as a result of the paradigm shift in weather conditions due to climate change. Siaya county showed highest prevalence of the RVFV followed by Busia county due to their proximity to Uganda that recently experienced RVF infection outbreak in one of the districts. Therefore, the kit can be adopted and deployed for rapid screening of RVFV in Kenya.This creates the need to focus and invest in the RVF infection control measures. The findings of this study calls for increased disease surveillance to cover wider western borderline counties and proper emergency preparedness in case of RVF outbreak so that the disease is managed on time to minimize losses during outbreaks. More importantly, RVF risk maps could contribute to data-driven decision-making for disease management when deploying vector control interventions.
Description
A Thesis Submitted in Fulfillment of the Requirements for the Award of the Degree of Doctor of Philosophy (Biotechnology) in the School of Pure and Applied Sciences of Kenyatta University June, 2024
Supervisors:
1. Mark Wamalwa
2. Richard Okoth Oduor
3. Yatinder Singh Binepal