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Conditions of malaria transmission in Dakar from 2007 to 2010

Libasse Gadiaga1*, Vanessa Machault234, Frédéric Pagès2, Abdoulaye Gaye1, Fanny Jarjaval2, Lydie Godefroy2, Birane Cissé5, Jean-Pierre Lacaux4, Cheikh Sokhna1, Jean-François Trape1 and Christophe Rogier26

Author Affiliations

1 Institut de Recherche pour le Développement, UMR 198; Unité Mixte de Recherche 6236 (URMITE), Route des Pères Maristes, BP 1386 Dakar, Sénégal

2 Unité Mixte de Recherche 6236 (URMITE), Institut de Recherche Biomédicale des Armées, Allée du Médecin colonel Jamot, Parc du Pharo, BP 60109, 13262 Marseille cedex 07, France

3 Centre National d'Etudes Spatiales - Service Applications et Valorisation - 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France

4 Observatoire Midi-Pyrénées, Laboratoire d'Aérologie, Centre National de la Recherche Scientifique, Université Paul Sabatier, 14 avenue Edouard Belin, 31400 Toulouse, France

5 Ecole Doctorale Eau, Qualité et Usages de l'Eau (EDEQUE), Université Cheikh Anta DIOP, Dakar, Sénégal

6 Institut Pasteur de Madagascar, B.P. 1274, Ambatofotsikely, 101 Antananarivo, Madagascar

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Malaria Journal 2011, 10:312  doi:10.1186/1475-2875-10-312

Published: 21 October 2011

Abstract

Background

Previous studies in Dakar have highlighted the spatial and temporal heterogeneity of Anopheles gambiae s.l. biting rates. In order to improve the knowledge of the determinants of malaria transmission in this city, the present study reports the results of an extensive entomological survey that was conducted in 45 areas in Dakar from 2007 to 2010.

Methods

Water collections were monitored for the presence of anopheline larvae. Adult mosquitoes were sampled by human landing collection. Plasmodium falciparum circumsporozoïte (CSP) protein indexes were measured by ELISA (enzyme-linked immunosorbent assay), and the entomological inoculation rates were calculated.

Results

The presence of anopheline larvae were recorded in 1,015 out of 2,683 observations made from 325 water collections. A water pH of equal to or above 8.0, a water temperature that was equal to or above 30°C, the absence of larvivorous fishes, the wet season, the presence of surface vegetation, the persistence of water and location in a slightly urbanised area were significantly associated with the presence of anopheline larvae and/or with a higher density of anopheline larvae. Most of the larval habitats were observed in public areas, i.e., freely accessible.

A total of 496,310 adult mosquitoes were caught during 3096 person-nights, and 44967 of these specimens were identified as An.gambiae s.l. The mean An. gambiae s.l. human-biting rate ranged from 0.1 to 248.9 bites per person per night during the rainy season. Anopheles arabiensis (93.14%), Anopheles melas (6.83%) and An. gambiae s.s. M form (0.03%) were the three members of the An. gambiae complex. Fifty-two An. arabiensis and two An. melas specimens were CSP-positive, and the annual CSP index was 0.64% in 2007, 0.09% in 2008-2009 and 0.12% in 2009-2010. In the studied areas, the average EIR ranged from 0 to 17.6 infected bites per person during the entire transmission season.

Conclusion

The spatial and temporal heterogeneity of An. gambiae s.l. larval density, adult human-biting rate (HBR) and malaria transmission in Dakar has been confirmed, and the environmental factors associated with this heterogeneity have been identified. These results pave the way for the creation of malaria risk maps and for a focused anti-vectorial control strategy.

Keywords:
Anopheles; Dakar; malaria; entomology; Plasmodium transmission; Human Biting Rate