| dc.description.abstract | Malaria is one of the main diseases that cause great morbidity and mortality in:
sub-Saharan Africa region. The prevalence and incidence of malaria in this region is
determined mostly by the mosquito vector species. Several measures 'andprogrammes
have been undertaken to control malaria vectors and reduce malaria incidence in Africa.
However, most of these measures have not been very successful. This has led to
proposals to use mosquitoes that are refractory to malaria parasite infection as one of the
options in malaria control programmes. Such a control strategy requires that population
genetic structure of the vector species is understood. The understanding of population
genetic structure of vector species will enable malaria entomologists to predict how
genes associated with refractoriness will spread through the vector populations.
Knowledge of vector population genetic structure is also useful for predicting the spread
of insecticide-resistance genes in a given vector population. Studies on the population
genetic structure of vector species have been carried out using various techniques and
markers. These include restriction fragment length polymorphism (RFLP), randomly
amplified polymorphic DNA (RAPD), chromosomal inversions, and microsatellite
DNA.
In this study,Anopheles arabiensis populations from two different types of breeding
habitats in Western Kenya were analysed using a total of eight microsatellite loci. The
aim of this study was to determine whether Anopheles arabiensis species partitioned
larval breeding habitats based on the habitat type. Two habitat types namely, transient
small size larval breeding habitats and permanent/semi-permanent large size larval
breeding habitats were considered and sampling done in three sites, two in Ahero and
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one in Nyakach. Specimen collection was done by pipetting and dipping using standard
World Health Organisation (WHO) procedures. A total of 500 mosquito larvae were.
collected. The specimens were processed by DNA extraction and fhen analysed using
polymerase chain reaction (Pf.R) and polyacrylamide gel electrophoresis (PAGE). The
data were analysed using GENEPOP version 3.2a software programme, which evaluated
Hardy- Weinberg equilibrium, allele frequencies, and genotypic frequencies. Levels of
genetic differentiation was analysed using G-like test available in GENEPOP.
Significance of multiple tests was evaluated using sequential rejective Bonferroni test
and binomial test.
There was polymorphism at SIX out of eight studied loci. Overall allelic and
genotypic frequency distribution at all loci deviated significantly from Hardy-Weinberg
equilibrium and pooled data from similar habitats and those from all breeding habitats at
Ahero also deviated from Hardy-Weinberg equilibrium (P < 0.05). The deviation from
Hardy- Weinberg equilibrium suggested lack of random mating and presence of
population sub-divisions. This meant that there was restricted gene flow between An.
arabiensis populations from similar habitat types in the study sites.
The G-like test showed genotypic differentiation at all loci across all populations.
The observed genotype distribution frequency was' not in agre.ement with the expected
frequency suggesting the presence of non-random mating and population sub-division.
The presence of sub-populations and non-random mating suggested that Anopheles
arabiensis did not partition their larval breeding habitats based on habitat type. The non
random mating and presence of sub-population may suggest presence of genetic
variability within Anopheles arabiensis populations in the study area. This may
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contribute to the diversity and stability of malaria transmission in study area. The
variation may also cause the proposed control measure based on vector replacement to·
be less effective. Therefore studies such as this, which, apply markers that can show '-' association with breeding habitats, can be useful in understanding whether the type of
breeding habitat may have effect on genetic variability of Anopheles arabiensis
populations at a local scale. | en_US |
