Outdoor host seeking behaviour of Anopheles gambiae mosquitoes following initiation of malaria vector control on Bioko Island, Equatorial Guinea

Abstract

BackgroundIndoor-based anti-vector interventions remain the preferred means of reducing risk of malaria transmission in malaria endemic areas around the world. Despite demonstrated success in reducing human-mosquito interactions, these methods are effective solely against endophilic vectors. It may be that outdoor locations serve as an important venue of host seeking by Anopheles gambiae sensu lato (s.l.) mosquitoes where indoor vector suppression measures are employed. This paper describes the host seeking activity of anopheline mosquito vectors in the Punta Europa region of Bioko Island, Equatorial Guinea. In this area, An. gambiae sensu stricto (s.s.) is the primary malaria vector. The goal of the paper is to evaluate the importance of An gambiae s.l. outdoor host seeking behaviour and discuss its implications for anti-vector interventions.MethodsThe venue and temporal characteristics of host seeking by anopheline vectors in a hyperendemic setting was evaluated using human landing collections conducted inside and outside homes in three villages during both the wet and dry seasons in 2007 and 2008. Additionally, five bi-monthly human landing collections were conducted throughout 2009. Collections were segregated hourly to provide a time distribution of host-seeking behaviour.ResultsSurprisingly high levels of outdoor biting by An. gambiae senso stricto and An. melas vectors were observed throughout the night, including during the early evening and morning hours when human hosts are often outdoors. As reported previously, An. gambiae s.s. is the primary malaria vector in the Punta Europa region, where it seeks hosts outdoors at least as much as it does indoors. Further, approximately 40% of An. gambiae s.l. are feeding at times when people are often outdoors, where they are not protected by IRS or LLINs. Repeated sampling over two consecutive dry-wet season cycles indicates that this result is independent of seasonality.ConclusionsAn. gambiae s.l. mosquitoes currently seek hosts in outdoor venues as much as indoors in the Punta Europa region of Bioko Island. This contrasts with an earlier pre-intervention observation of exclusive endophagy of An. gambiae in this region. In light of this finding, it is proposed that the long term indoor application of insecticides may have resulted in an adaptive shift toward outdoor host seeking in An. gambiae s.s. on Bioko Island.

A Review of Mosquitoes Associated with Rift Valley Fever Virus in Madagascar

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A second chance to tackle African malaria vector mosquitoes that avoid houses and don't take drugs

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Plasmodium falciparum infection rates for some Anopheles spp. from Guinea-Bissau, West Africa

“…Consequently no general comments about the degree of exophily of A. gambiae in Guinea-Bissau can be made. However, evidence of exophily by the major malaria vector A. gambiae in this study and by others in West Africa ( Reddy et al , 2011; Tchouassi et al , 2012) raises the concern of the long term effectiveness of Indoor Residual Spraying (IRS) and Long lasting Insecticide-treated Nets (LLINs) in reducing outdoor transmission of malaria especially before bedtime and by people sleeping outdoors. The relatively high infection rate of 11.1% of A. melas in Guinea-Bissau together with its tendencies to be both endophilic and exophilic and have a high human blood index ( Sharp et al , 2007; Tuno et al , 2010) make the species a significant vector, which may also be hard to control by reliance on ITNs and LLINs.…”