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. 2011 Oct 21:10:312.
doi: 10.1186/1475-2875-10-312.

Conditions of malaria transmission in Dakar from 2007 to 2010

Libasse Gadiaga  1 , Vanessa Machault, Frédéric Pagès, Abdoulaye Gaye, Fanny Jarjaval, Lydie Godefroy, Birane Cissé, Jean-Pierre Lacaux, Cheikh Sokhna, Jean-François Trape, Christophe Rogier
Affiliations

Conditions of malaria transmission in Dakar from 2007 to 2010

Libasse Gadiaga et al. Malar J. .

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.

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Figures

Figure 1
Figure 1
Spatial distribution of 45 studied areas in Dakar and their period of study.
Figure 2
Figure 2
Hourly distribution of An. gambiae s.l. bites in 45 studied areas in Dakar, from 2007 to 2010.
Figure 3
Figure 3
Anopheles gambiae s.l. HBR and rainfall events in 10 studied areas in September-October 2007, 30 studied areas in July 2008 - June 2009 and 30 studied areas in July 2009 - June 2010.
Figure 4
Figure 4
Mean An. gambiae s.l. Rainy HBR for 45 studied areas in Dakar, for 2007, 2008 and 2009 rainy seasons (Sept-Oct).
Figure 5
Figure 5
Mean An. gambiae s.l. Rainy HBR for 45 studied areas in Dakar, for 2007, 2008 and 2009 rainy seasons (Sept-Oct), spatial distribution.
Figure 6
Figure 6
Mean An. gambiae s.l. Dry HBR for the studied areas in Dakar, for 2008 and 2009 dry seasons (Nov-Jun).
Figure 7
Figure 7
Temporal variations of Anopheles adult density fraction and Anopheles larval density fraction. Data collected in 45 studied areas in Dakar in Sept-Oct 2007 and Jul 2008-April 2010.
See this image and copyright information in PMC

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