Survival Rates and Blood Meal Patterns of Aedes aegypti and Aedes simpsoni Mosquitoes in Kerio Valley and Rabai Arbovirus Ecologies, Kenya
Kamau, Winnie W.
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Understanding the vectorial capacity for arboviruses transmission can allow for improved prediction and of arboviral disease outbreaks and control. Like other vector-borne diseases, transmission of arboviruses is influenced by vector bionomic traits including age structure and vector feeding habits. The current study investigated the survival rates, blood meal patterns and the human blood feeding habits in field collected populations of Aedes aegypti and Aedes simpsoni mosquitoes, which are vectors of dengue virus (DENV) and yellow fever virus (YFV), respectively, in East Africa. Adult female mosquitoes analysed were trapped during the day using CO2-baited BG Sentinel traps from peri-urban Rabai, Kilifi County (dengue-endemic) and rural Kerio Valley, Baringo County (with a history of yellow fever outbreak) during the period between August 2019 to February 2020. The mean parity rates following dissection and microscopic examination of ovarian tracheoles was high for Ae. simpsoni (85% (n=539) that did not vary between the trapping periods, while in Ae. aegypti was 74.9% (n=735) but varied between the trapping periods. Assuming a 3-day gonotrophic cycle, these translated to a high daily survival rate and longevity ranging between 15.8-19.7 days and 7.7-12.4 days in Ae. simpsoni and Ae. aegypti, respectively. Analysis of blood fed cohorts through DNA sequencing of the12S mitochondrial rRNA fragment showed a diverse host feeding range for Ae. aegypti with estimated human blood index (HBI) of 0.53. HBI did not vary between mitochondrial lineages indicative of domestic and forest genetic forms of Ae. aegypti. The genetic forms of Ae. aegypti were determined by PCR of a cox1 gene fragment and then sequencing followed by phylogenetic reconstruction. Similarly, Ae. simpsoni complex also exhibited a broad host feeding range, with Ae. bromeliae being the most predominant sub-species as determined using Internal Transcribed Spacer 2 (ITS2) PCR sequences, which exhibited a low HBI (0.18 and 0.33 in Rabai and Kerio Valley, respectively). Phylogenetic analysis also suggested the presence of a species which is yet to be described within the Ae. simpsoni complex, demonstrating human blood feeding tendency. The species diversity in the Ae. simpsoni complex may well be greatly higher than earlier thought, which requires more studies. Overall, both species exhibited high survival/longevity that could lead to high vectorial capacity for YFV and DENV transmission. Additionally, the low human blood meals of both Ae. aegypti and Ae. simpsoni cohorts indicated a high capacity for zoonotic transmission of other pathogen and therefore a need for continued efforts to control these vectors. These findings demonstrated the applicability to include other bionomic parameters such as vector competence, which defines vectorial capacity, for an effective understanding of spread and recurrence risk of these arboviruses. In addition to enhance cost effectiveness interventions (e.g. vaccines) and prediction of diseases occurrence, there is urgency to generate surveillance information of vector population founded on genotype analyses.