Regional Organizations and Conflict Intervention in Africa: Case of Inter-Governmental Authority for Development in South Sudan, 2011-2022
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Date
2025-06
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Kenyatta University
Abstract
Malaria remains a signifianct global health challenge, with Africa bearing a
disproportionate burden. In Kenya, Anopheles arabiensis has emerged as a key malaria
vector, particularly in coastal regions, following shifts in vector dynamics due to control
measures. While bacteria in oviposition sites are known to influence mosquito egg-laying
choices, the precise roles of these microbial communities in attracting or repelling An.
arabiensis are not fully elucidated. This study aimed to characterize physicochemical
parameters and bacterial communities in preferred and non-preferred oviposition sites of
An. arabiensis in Kwale County, Kenya, and to evaluate the role of these bacteria in
mediating oviposition. The study had three objectives: (i) To determine the
physicochemical characteristics of Anopheles arabiensis larval habitats; (ii) To identify
bacterial profiles in oviposition sites of Anopheles arabiensis in malaria-endemic regions
of Kwale County; and (iii) To evaluate the role of bacterial communities in attracting
Anopheles arabiensis mosquitoes to oviposition sites. The study identified distinct larval
habitats, with preferred sites exhibiting significantly higher An. arabiensis larval densities
(M >10 larvae/dip) compared to non-preferred sites (M < 10 larvae/dip) (F (1, 84) =
740.229, p<.001). Habitat type also significantly influenced larval density (F (2, 84) =
81.246, p<.001), with rain pools supporting the highest densities (M = 33.33 larvae/dip)
and proving significantly more favourable than hoofprints and swamps (p<.001 for both
comparisons). Physicochemical analysis revealed significant differences: preferred sites
had higher mean temperatures (M = 33.77 °C, SD = 0.85 vs. M = 31.50 °C, SD = 0.96; t(4)
= 3.053, p = .038), higher electrical conductivity (M = 1289.33 µS/cm, SD = 194.74 vs. M
= 542.67 µS/cm, SD = 115.98; t(4) = 5.076, p = .005), higher total dissolved solids (M =
581.67 mg/L, SD = 82.78 vs. M = 273.33 mg/L, SD = 58.38; t(4) = 5.272, p = .006), and a
lower pH (M = 7.10, SD = 0.15 vs. M = 8.03, SD = 0.40; t(4) = -3.837, p = .019) compared
to non-preferred sites. Bacterial populations were isolated, and 16S rRNA gene sequencing
revealed distinct profiles: Enterobacter species predominated in preferred sites, while
Plualibacter species were more common in non-preferred sites. Bioassays demonstrated a
significant preference for bacterial isolates from preferred sites (Mann-Whitney U = 0.000,
p = .003). Specifically, Enterobacter sp. strain CDB3 (from a preferred site) elicited the
highest mean number of eggs (M = 126.00, SD = 11.53) and an Oviposition Actrivity Index
(OAI) of 0.84. Conversely, Pluralibacter gergoviae strain PGBM32 and an uncultured
bacterium clone (both from non-preferred sites) attracted no eggs (OAI = -1.00). These
findings highlight that specific physicochemical conditions and associated bacterial
communities, particularly Enterobacter species, significantly attract An. arabiensis for
oviposition, whereas others, like certain Pluralibacter species, may act as deterrents. This
research underscores the potential for developing novel, microbe-based “push-pull”
strategies for sustainable malaria vector control, to control mosquito breeding behaviours.
This study suggests eco-friendly bactericides can reduce mosquito egg laying by removing
attractant bacteria, aiding malaria vector control in malaria-prone areas.
Description
A Thesis Submitted In Partial Fulfillment of the Requirements for the Award of the Degree of Master of Arts in International Relations and Diplomacy in the School of Law, Arts and Social Sciences of Kenyatta University, April 2025.
Supervisor
1. James Nonoh
2. Sauda Swaleh
3. Regina Ntabo