Ecology of Immature Stages of the Dengue Fever Vector Aedes Aegypti (L.) (Diptera: Culicidae) in Rural and Urban Sites of the Southern Coast of Kenya

Abstract

Aedes aegypti is the most important vector of dengue fever and several other arboviruses of public health such as Zika and Chikungunya. Currently vector management is the only available option for disease control. Efficient vector control and development of meaningful surveillance methods depends on a good understanding of vector ecology of which little is known in Kenya. The objectives of this study were to characterize breeding habitats of Ae. aegypti, determine seasonal distribution and abundance of Aedes aegypti larvae and pupae in rural and urban sites in coastal Kenya, identify households that are consistently productive for Ae. aegypti pupae and to determine susceptibility of Aedes aegypti larvae to the biological larvicide Bacillus thuringiensis var israelensis (Bti). Entomological, demographic and environmental data was collected from twenty sentinel households once a month for 24 months (June 2014 to May 2016) in the rural and urban sites of southern coast of Kenya. All water holding containers in and around houses were inspected for Ae aegypti larvae and pupae and oviposition traps set weekly in the study households. Susceptibility of Ae aegypti larvae to a biocontrol agent Bacillus thuringiensis var israelensis (Bti) was evaluated. Of the 6,566 container visits, only 5.11%, were found positive for Ae aegypti immatures in the study sites. In both sites significantly more Ae aegypti positive wet containers were found outdoors than indoors. The most important containers were buckets, drums and tyres which produced over 70% of all the immatures in both sites. The median number of months in which pupae were observed in households was 4 and ranged from 0 to 15.The strongest risk factor for pupal abundance was presence of high habitat counts (OR = 1.27, 95% CI 1.00-1.60). Initial efficacy results showed that Bacillus thuringiensis AM65-52 WG

formulation eliminated 100% of larvae in 24 hours. The results of this study indicate that breeding habitats of Ae. aegypti are abundant outdoors , but, only a few containers are productive. Further, Ae. aegypti pupal persistence at the household level in urban and rural sites was observed. High counts of breeding containers was associated with increased risk of pupal abundance.in households. Targeting productive containers and households that exhibit high pupal abundance and persistence in vector control interventions may result into costeffective management of the dengue vector and arboviral transmission in this region.