Abstract
BackgroundThe scaling up of malaria vector control efforts in Africa has resulted in changing the malaria vectorial systems across different ecological settings. In view of the ongoing trends in vector population dynamics, abundance, species composition and parasite infectiousness, there is a need to understand vector distribution and their contribution to malaria transmission to facilitate future planning of control strategies. We studied indoor and outdoor malaria transmission dynamics and vector population variability of Anopheles mosquitoes in Taveta district along the Kenyan Coast.MethodsAnopheles mosquitoes were collected indoors and outdoors in 4 ecologically different villages using CDC light traps (both indoor and outdoor) and aspiration method (day resting indoors; DRI) methods. Mosquitoes were examined for infection with P. falciparum sporozoites and blood feeding preferences using enzyme linked immunosorbent assay (ELISA). The An. gambiae and An. funestus complexes were identified by PCR technique to determine the sibling species composition.ResultsA total of 4,004 Anopheles mosquitoes were collected consisting of 34.9%% (n = 1,397) An. gambiae s.1., 28.1% (n = 1,124) An. funestus s.l., 33.5% (n = 1,340) An. coustani and 3.6% (n = 143) An. pharoensis. A total of 14,654 culicine mosquitoes were collected, mainly Cx. quinquefasciatus. Of the total Anopheles collected, 3,729 were tested for P. falciparum sporozoite infection. The sporozoite transmission was found to be occurring both indoors and outdoors. The overall sporozoite infectivity was 0.68% (n = 2,486) indoors and 1.29% (n = 1,243) outdoors. Indoor and outdoor sporozoite infectivity and the vectorial systems varied across the 4 ecological villages. Entomological inoculation rates for the 4 villages indicate that there was site-to-site variation. In the 4 villages, Mwarusa had the highest EIRs with An. arabiensis, An. funestus and An. coustani contributing to 23.91, 11.96 and 23.91 infectious bites per person per year ib/p/year respectively. In Kiwalwa and Njoro outdoor EIR was significantly higher than indoors.ConclusionsThis study shows that malaria transmission is occurring both indoors and outdoors. The main vectors are An. arabiensis, An. funestus and An. coustani indoors while An. coustani is playing a major role in outdoor transmission. Effective malaria control programmes, should therefore include tools that target both indoor and outdoor transmission.
Highlights
The scaling up of malaria vector control efforts in Africa has resulted in changing the malaria vectorial systems across different ecological settings
Considered unimportant, the role of these vectors in malaria transmission has increased over the years spurred by the widespread use of insecticide-treated bed nets that are selectively decimating An. gambiae and An. funestus populations while impacting little on complementally species and one primary vector An. arabiensis [10,11,12]
In Kiwalwa and Njoro outdoor entomological inoculation rates (EIRs) was significantly higher than indoors
Summary
The scaling up of malaria vector control efforts in Africa has resulted in changing the malaria vectorial systems across different ecological settings. Considered unimportant, the role of these vectors in malaria transmission has increased over the years spurred by the widespread use of insecticide-treated bed nets that are selectively decimating An. gambiae and An. funestus populations while impacting little on complementally species and one primary vector An. arabiensis [10,11,12]. In order to maintain recent gains in malaria control and to proceed towards the intended target of malaria elimination, it will be important to develop strategies to interrupt malaria transmission by these vectors. This effort requires indepth knowledge of the ecology and behavior of these vectors. Effective vector control measures decrease the incidence of malaria infections because there is a linear relationship between EIRs and malaria incidence [6,16,17,18]
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