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Highly focused anopheline breeding sites and malaria transmission in Dakar.

Machault V, Gadiaga L, Vignolles C, Jarjaval F, Bouzid S, Sokhna C, Lacaux JP, Trape JF, Rogier C, Pagès F - Malar. J. (2009)

Bottom Line: Seven out of 1,101 An. gambiae s.l. were found to be positive for P. falciparum (CSP index = 0.64%).Some physico-chemical characteristics of water bodies were associated with the presence/absence of anopheline larvae and with larval density.A very close parallel between larval and adult densities was found in six of the ten study areas.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unité d'Entomologie Médicale, Equipe 7 Maladies Emergentes et Moustiques, Institut de Médecine Tropicale du Service de Santé des Armées, Allée du Médecin colonel Jamot, Parc du Pharo, 13262 Marseille cedex 07, France. vanessamachault@yahoo.com.br

ABSTRACT

Background: Urbanization has a great impact on the composition of the vector system and malaria transmission dynamics. In Dakar, some malaria cases are autochthonous but parasite rates and incidences of clinical malaria attacks have been recorded at low levels. Ecological heterogeneity of malaria transmission was investigated in Dakar, in order to characterize the Anopheles breeding sites in the city and to study the dynamics of larval density and adult aggressiveness in ten characteristically different urban areas.

Methods: Ten study areas were sampled in Dakar and Pikine. Mosquitoes were collected by human landing collection during four nights in each area (120 person-nights). The Plasmodium falciparum circumsporozoite (CSP) index was measured by ELISA and the entomological inoculation rates (EIR) were calculated. Open water collections in the study areas were monitored weekly for physico-chemical characterization and the presence of anopheline larvae. Adult mosquitoes and hatched larvae were identified morphologically and by molecular methods.

Results: In September-October 2007, 19,451 adult mosquitoes were caught among which, 1,101 were Anopheles gambiae s.l. The Human Biting Rate ranged from 0.1 bites per person per night in Yoff Village to 43.7 in Almadies. Seven out of 1,101 An. gambiae s.l. were found to be positive for P. falciparum (CSP index = 0.64%). EIR ranged from 0 infected bites per person per year in Yoff Village to 16.8 in Almadies. The An. gambiae complex population was composed of Anopheles arabiensis (94.8%) and Anopheles melas (5.2%). None of the An. melas were infected with P. falciparum. Of the 54 water collection sites monitored, 33 (61.1%) served as anopheline breeding sites on at least one observation. No An. melas was identified among the larval samples. Some physico-chemical characteristics of water bodies were associated with the presence/absence of anopheline larvae and with larval density. A very close parallel between larval and adult densities was found in six of the ten study areas.

Conclusion: The results provide evidence of malaria transmission in downtown Dakar and its surrounding suburbs. Spatial heterogeneity of human biting rates was very marked and malaria transmission was highly focal. In Dakar, mean figures for transmission would not provide a comprehensive picture of the entomological situation; risk evaluation should therefore be undertaken on a small scale.

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Cap-Vert peninsula and localization of the ten study areas.
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Figure 1: Cap-Vert peninsula and localization of the ten study areas.

Mentions: Site selection was done on the basis of a SPOT-5 (Satellite Pour l'Observation de la Terre) satellite image (CNES 2006, Distribution Spot Image SA) acquired in October 2006 (Figure 1) and classified using a supervised technique which allowed to affect each pixel of the image to a land cover. Result of this process provided a map of vegetation, water, bare soils and different types of urban areas. Based on this land cover map, the study areas were sampled in order to cover as many different environments as possible, in terms of type of urbanization and presence of vegetation. Each site was delimited on the ground to cover an area of about 200 × 200 m, depending on the technical and logistical limitations presented by the landscape (Figure 1). Geographic coordinates are given for the centre of each study area.


Highly focused anopheline breeding sites and malaria transmission in Dakar.

Machault V, Gadiaga L, Vignolles C, Jarjaval F, Bouzid S, Sokhna C, Lacaux JP, Trape JF, Rogier C, Pagès F - Malar. J. (2009)

Cap-Vert peninsula and localization of the ten study areas.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2713260&req=5

Figure 1: Cap-Vert peninsula and localization of the ten study areas.
Mentions: Site selection was done on the basis of a SPOT-5 (Satellite Pour l'Observation de la Terre) satellite image (CNES 2006, Distribution Spot Image SA) acquired in October 2006 (Figure 1) and classified using a supervised technique which allowed to affect each pixel of the image to a land cover. Result of this process provided a map of vegetation, water, bare soils and different types of urban areas. Based on this land cover map, the study areas were sampled in order to cover as many different environments as possible, in terms of type of urbanization and presence of vegetation. Each site was delimited on the ground to cover an area of about 200 × 200 m, depending on the technical and logistical limitations presented by the landscape (Figure 1). Geographic coordinates are given for the centre of each study area.

Bottom Line: Seven out of 1,101 An. gambiae s.l. were found to be positive for P. falciparum (CSP index = 0.64%).Some physico-chemical characteristics of water bodies were associated with the presence/absence of anopheline larvae and with larval density.A very close parallel between larval and adult densities was found in six of the ten study areas.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unité d'Entomologie Médicale, Equipe 7 Maladies Emergentes et Moustiques, Institut de Médecine Tropicale du Service de Santé des Armées, Allée du Médecin colonel Jamot, Parc du Pharo, 13262 Marseille cedex 07, France. vanessamachault@yahoo.com.br

ABSTRACT

Background: Urbanization has a great impact on the composition of the vector system and malaria transmission dynamics. In Dakar, some malaria cases are autochthonous but parasite rates and incidences of clinical malaria attacks have been recorded at low levels. Ecological heterogeneity of malaria transmission was investigated in Dakar, in order to characterize the Anopheles breeding sites in the city and to study the dynamics of larval density and adult aggressiveness in ten characteristically different urban areas.

Methods: Ten study areas were sampled in Dakar and Pikine. Mosquitoes were collected by human landing collection during four nights in each area (120 person-nights). The Plasmodium falciparum circumsporozoite (CSP) index was measured by ELISA and the entomological inoculation rates (EIR) were calculated. Open water collections in the study areas were monitored weekly for physico-chemical characterization and the presence of anopheline larvae. Adult mosquitoes and hatched larvae were identified morphologically and by molecular methods.

Results: In September-October 2007, 19,451 adult mosquitoes were caught among which, 1,101 were Anopheles gambiae s.l. The Human Biting Rate ranged from 0.1 bites per person per night in Yoff Village to 43.7 in Almadies. Seven out of 1,101 An. gambiae s.l. were found to be positive for P. falciparum (CSP index = 0.64%). EIR ranged from 0 infected bites per person per year in Yoff Village to 16.8 in Almadies. The An. gambiae complex population was composed of Anopheles arabiensis (94.8%) and Anopheles melas (5.2%). None of the An. melas were infected with P. falciparum. Of the 54 water collection sites monitored, 33 (61.1%) served as anopheline breeding sites on at least one observation. No An. melas was identified among the larval samples. Some physico-chemical characteristics of water bodies were associated with the presence/absence of anopheline larvae and with larval density. A very close parallel between larval and adult densities was found in six of the ten study areas.

Conclusion: The results provide evidence of malaria transmission in downtown Dakar and its surrounding suburbs. Spatial heterogeneity of human biting rates was very marked and malaria transmission was highly focal. In Dakar, mean figures for transmission would not provide a comprehensive picture of the entomological situation; risk evaluation should therefore be undertaken on a small scale.

Show MeSH
Related in: MedlinePlus