Spatial and temporal distribution of Aedes mosquitoes, Dengue and Chikungunya Viruses and their Phylogeny along the Coastline of Kenya
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Date
2020-07
Authors
Ngala, Chome Jonathan
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
There are arthropod-borne disease outbreaks as a result of pathogen influx
including arboviruses which are transmitted by strains of Aedes species that occur
periodically in varying spots in Kenya. However, there has been paucity of
documented information on the epidemiology of Aedes mosquitoes involved in
transmission of different strains of viruses. This cross sectional study determined
spatial and temporal distribution of Aedes mosquitoes, Dengue and Chikungunya
viruses, and their phylogeny and vector-virus co-infections during dry and wet
seasons. Indoor and outdoor sampling of adults Aedes mosquitoes was done using
Biogent Sentinel trap baited with solid carbon dioxide and Prokopack aspiration
technique. Aedes mosquitoes were identified and sorted according to collection
site, sex, physiological status and species using their morphological features and
molecular techniques. Sentinel sites coordinates were recorded by Global
Positioning System receiver with spatial and temporal maps generated using
ArcGeographical information system. RNA was extracted from Aedes mosquitoes
using TrizolĀ®. Identification of Aedes species, Dengue and Chikungunya was
done using Polymerase Chain Reaction. Sequencing of amplicons was done using
Sanger high-throughput technique and their proportions analysed by R-statistics.
Phylogeny tree files were generated using Randomised Accelerated Maximum
Likelihood and trees plotted using interactive tree of life. A total of 37,220 Aedes
mosquitoes belonging to eight species were collected and grouped in pools of 20
mosquitoes. Aedes aegypti formosus was dominant at 62.5%. Aedes aegypti
aegypti was identified for the first time along the Coastline of Kenya. There was
no effect of season on the distribution and proportion of Aedes species along the
Coastline. Aedes mosquitoes belonged to the upper clade of the phylogenetic tree.
Four serotypes of Dengue virus were identified with DENV-4 identified for the
first time in Aedes mosquitoes in the region. Only the East/Central/South African
(ECSA) genotype of Chikungunya virus was isolated and seasons did not influence
the distribution of both viruses along the Coastline (p>0.001). Aedes mosquitoes
were closely related to previous isolates and to those from Uganda, Senegal and
Thailand. DENV-1 isolates were closely related to those from India, DENV-2
isolates were closely related to those from Pakistan, and DENV-3 isolates were
closely related to those from Brazil while DENV-4 isolates were closely related to
those from Haiti. Chikungunya ECSA genotype isolates were closely related to
previous Kenyan isolates and to those from South Africa and Tanzania. There
were co-infections of Dengue and Chikungunya viruses in Aedes mosquitoes.
Aedes aegypti s.l and Aedes pembaensis had co-infections of all viruses.
Prevalence of Dengue virus was at 7.9% while Chikungunya was at 2.1%. These
results are important as they give information on areas of high risk for the virus
outbreaks. Surveillance of entomological infection by viruses and implementation
of their appropriate control measures should be taken by the Ministry of Health.
Description
A Research Thesis submitted in Partial Fulfilment for the Award of the Degree of Doctor of Philosophy in Infectious diseases (Medical Parasitology) in the School of Medicine, Kenyatta University
Keywords
Spatial, Temporal distribution, Aedes mosquitoes, Dengue, Chikungunya Viruses, Phylogeny, Coastline, Kenya