Genetic differentiation, vector competence to dengue 2 viruses and host preferences of coastal and inland aedes aegypti populations from Kenya
Burugu, Marion Warigia
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The mosquito, Aedes aegypti is the main vector of dengue viruses responsible for millions of dengue fever and hundred of thousands of dengue hemorrhagic fever cases annually in tropical regions of the world. At the Kenyan coast, dengue incidences continue to be reported while inland, the disease is not documented. Since Aedes aegypti is widely distributed in Kenya, characterization of patterns of gene flow and genetic differentiation between Ae. Aegypti populations from these regions was necessary. Additionally, the vector competence of these populations and their bloodmeal host preferences, which influence disease epidemiology need to be established before implementation of any control strategy. A hierarchical population genetic study was conducted among 30 Aedes aegypti populations from coast and inland parts of Kenya. Single-strand conformation polymorphism analysis was used to examine genetic variation in a 389 - base pair region of the NADH dehydrogenase subunit 4 mitochondria) DNA gene (ND4). Vector competence to dengue 2 viruses was examined using immunofluorescence procedure and host-feeding preference determined using enzyme linked immunoabsorbent assay technique. Fourteen haplotypes were identified from a total of 1005 individual Ae. aegypti. Phylogenetic analysis of these haplotypes indicated two maternal lineages. Gene flow estimates demonstrated that coastal populations were relatively panmictic implying that dispersal in search for oviposition sites and human activities are factors that shaped the genetic structure in this area. Inland populations exhibited relatively restricted gene flow especially between seasons (Nm <1), reflecting possible bottleneck effects between seasons. There was no barrier to gene flow and human movement may be contributing significantly to the observed levels of gene flow. Aedes aegypti from coast region were more susceptible to dengue 2 viruses (19.05 - 77.7 % infection rates) than those of inland region (10.26 - 46.2 %), however, this difference in infection rates was not statistically significant (X2 = 1.3659, p>0.05). Restricted gene flow and low infection rates of the inland collections may explain why there has been no documented outbreak or incidence of dengue viruses circulating at the inland region. A total of 147 individual mosquitoes were positive for different antisera, 65.3 % of which had fed on human as a single host. Mixed feeding was recorded in 19.04 % of the individuals, (89.28 %) with both humans and baboon blood. Overall, human blood index was 84.82 %. This shows that Ae. aegypti has high preference for human blood more than other hosts even in the presence of other hosts indicating the anthropophilic nature of this species. Overall low genetic diversity in ND4 gene in coastal and inland Kenya Aedes aegypti populations was demonstrated suggesting that these populations could be more ancestral in nature and have not undergone a major evolution over the years.