Abstract
BackgroundPrevious 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.MethodsWater 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.ResultsThe 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.ConclusionThe 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.
Highlights
Previous studies in Dakar have highlighted the spatial and temporal heterogeneity of Anopheles gambiae s.l. biting rates
When drawn at appropriate scales, entomological maps of the spatial and temporal distribution of malaria vector larvae and adults could provide valuable information for targeted malaria control and the selective allocation of resources. Drawing such maps could theoretically be based on exhaustive entomological studies that cover the entire city over several years, but identification of the environmental factors that are associated with malaria transmission and the remotely sensed measurement of those factors could lead the way to an operational malaria risk mapping
From 2005 to 2007 in Dakar, entomological data have been collected from several areas [6,8], and a portion of these data have allowed for a preliminary step towards malaria risk mapping, which is based on remotely sensed data, by setting up two risk maps for the years 1996 and 2007 [26]
Summary
Previous studies in Dakar have highlighted the spatial and temporal heterogeneity of Anopheles gambiae s.l. biting rates. When drawn at appropriate scales, entomological maps of the spatial and temporal distribution of malaria vector larvae and adults could provide valuable information for targeted malaria control and the selective allocation of resources. Drawing such maps could theoretically be based on exhaustive entomological studies that cover the entire city over several years, but identification of the environmental factors that are associated with malaria transmission and the remotely sensed measurement of those factors could lead the way to an operational malaria risk mapping. For more accurate and precise malaria risk mapping, the objective of the present study was to investigate the environmental conditions associated with malaria transmission in-depth in 45 studied areas of Dakar and its suburbs from the years 2007 to 2010
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