Spatial-Temporal Changes of Mosquitoes Dynamics and Risks of Arboviruses to Livestock during a Period of Extreme Flooding of Lake Baringo, Kenya
Loading...
Date
2021
Authors
Kamau, Samuel Kabochi
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
The ecology of mosquitoes and associated arboviruses are heavily influenced by precipitation and retention of water in the environment. In 2011 to 2014, unprecedented flooding occurred in Lake Baringo flooding expansive area and inundated over 88km2 of the shoreline. The impact of this on animal health, livelihoods and ecology generated a lot of interest among stakeholders. The current study was aimed at assessing the spatial-temporal changes of mosquito abundance, diversity and associated risks to arboviruses in order to enrich control strategies for mosquitoes and zoonoses. This was a longitudinal study carried out for one year from October 2012 to October 2013. It analysed mosquito ecology, identified mosquitoes to species level where possible, characterized arboviruses and determined disease prevalence from livestock. Mosquitoes were trapped using Centre for Disease Control (CDC) light traps in three ecological zones namely swamp marshy habitat, flooded lake shoreline and dry rangeland. Blood was drawn from livestock to determine presence of arboviruses. A total of 386,624 individual mosquitoes were captured. The Anopheline mosquitoes constituted genus Anopheles, while the Culicinae constituted 10 genera namely Aedes, Culex, Mansonia, Hodgesia, Uranotaenia, Coquillettidia, Aedeomyia, Ficalbia, Theobaldia and Orthodomyia. Mosquitoes of genus Mansonia were the dominant species in the basin and accounted for 84.9% with 97.8% coming from flooded lake shoreline habitat. Genus Aedes formed 0.1% of total mosquito catches from the basin with 96.9% of the individuals caught coming from swamp marshy habitat. Isolated viruses were Culex flavivirus in mosquitoes, Aedes flavivirus and Rift Valley Fever virus in livestock blood. This study reports for the first time detection of nucleic acid for Aedes flavivirus, an insect specific flavivirus, from livestock blood even though it does not replicate in vertebrate cells. Of eight (8) sequences of isolated virus for Rift Valley Fever (RVF), only three (3) sequences were 100% similar and the other five (5) exhibited alterations at various nucleotide base positions. Results from Next Generation Sequencing produced nucleotide sequences identical to Aedes albopictus mosquito species for the first time in the area. The mean catches of mosquitoes between the three habitats from Lake Baringo basin was significantly different at (F (2, 27) =3.54; P=0.04). Also significantly different were mean catches of mosquitoes at night from communal grazing areas and homestead at (F (11, 12) =2.87; P=0.04). The flooded lake shoreline had the lowest diversity of Simpson’s Index at 0.13 due to dominance by mosquitoes of genus Mansonia. The swamp marshy and dry rangeland areas were more diverse in mosquito genera with Simpson’s Indices of 0.56 and 0.57 respectively. Overall infection prevalence in livestock with RVF virus was 10.4% with the highest risk encountered from swamp marshy habitat (7.8%), flooded shoreline (2.6%) and lowest at dry rangeland (0%). The risk of infection with arboviruses was significantly lower in the dry rangeland habitat than in flooded shoreline at (t (6) = 1.94; P=0.024). The findings indicate that unprecedented flooding altered the environmental tolerance range of different mosquito species and ecology and this affected the spatial-temporal parameters impacting on mosquitos’ composition, abundance and diversity in the expansive lake shoreline habitat. This increased the risks of transmission and infection with mosquito-borne arboviruses to livestock. It is recommended that both the relevant departments and agencies for livestock and human health develop a strategic approach for the control and mitigation against RVFV in wetlands and floods prone areas.
Description
A Thesis Submitted in Fulfilment of the Requirement for the Award of Doctor of Philosophy (Entomology) in the School of Pure and Applied Sciences, Kenyatta University, September, 2021
Keywords
Spatial-Temporal Changes, Mosquitoes Dynamics, Risks of Arboviruses, Livestock, Period of Extreme Flooding, Lake Baringo, Kenya