Dakar study area

Dakar Dakar is the westernmost point of Africa, located at 14°40’20“North, 17°25’22” West. The capital city of Senegal, with 1,030,594 inhabitants, covers the major part of the Cap Vert peninsula. Altitude doesn’t exceed 104m. The population of Dakar area is estimated at 2.45 million people representing 20% of the Senegalese population. The estimate density is 12 233 inhabitants per km².

The Cap Vert peninsula is located in the Atlantic Sudan zone and has a “subcanarian” mild climate. Two distinct seasons exist : a hot and wet season from June to November (maximum average temperature 28.2°C in October), and a cool and dry season from December to May (minimum average temperature 20.4°C in February). The first rains generally occur at the end of June or the beginning of July, and the last ones occur at the beginning of October. In 2007, 2008 and 2009, the annual rainfall was respectively 178 mm, 510 mm and 565 mm (data from the national weather agency).

In Dakar, the main malaria vector is Anopheles arabiensis. The main potential breeding sites for this species are permanent or temporary water collections as: . natural marshy hollows, . dugs for market garden irrigation, . ditches and car-tracks on the road, . canals …

Adaptations of the anopheline vectors to new breeding sites (tree holes, polluted water) are reported from many urban areas in Africa.

Malaria prevalence is very low in Dakar and its urban periphery but recent work demonstrated that transmission locally exists. Malaria transmission is seasonal and mainly occurs in the wet season where aggressiveness can reach about 200 anopheles bites per person per night. Entomological inoculation rate is about 6‰. Someone who would not use any protective device could receive until 1 infected bite every 4 days in the middle of the wet season.

In situ data

The study is conducted in 45 different areas of downtown Dakar, as well as in Pikine, Thiaroye and Guediawaye, three of its satellite cities. The choice of the studied zones is done in order to cover as many diverse environments as possible in terms of type of urbanization, road network, vegetation and socio-economic level. Each site is delimited on the ground to cover an area of about 200 x 200 m, depending on the technical and logistical limitations presented by the landscape. Field study is undertaken in September and October 2007 and from July 2008 to June 2010 so three rainy seasons and two dry seasons is covered. In summary, 10 zones are studied in September-October 2007, 30 zones in July 2008-June 2009 and 30 zones in July 2009-June 2010. Each zone is followed during one or two years.

Larval sampling

Open water collections in the studied areas are monitored every 10 days for physico-chemical and environmental characterization and the presence of anopheline larvae is researched. When anopheline specimens are found, larval density is calculated as the number of larvae (all instars) and pupae (further emerged and identified at the laboratory) per dip and recorded for each water collection. Larvae are taken to the laboratory for emergence and further species identification by PCR technique.

Adult mosquitoes sampling

Adult mosquito sampling is carried out once every two weeks during September-October 2007 as well as during both extended 2008 and 2009 wet seasons (July to December), and once every month during both 2009 and 2010 dry seasons (January to June). Human landing catches of adult mosquitoes is conducted both indoors and outdoors in each studied areas, from 7:00 p.m. to 7:00am. For every zone, one catching point is indoors and two are outdoors. Mosquitoes sampled by human landing collection is identified morphologically and by molecular methods. The Plasmodium falciparum circumsporozoïte (CSP) indexes is measured by ELISA, and the entomological inoculation rates (EIR) are calculated for the 45 areas.