Malaria transmission in Dakar: A two-year survey

BACKGROUND: According to entomological studies conducted over the past 30 years, there was low malaria transmission in suburb of Dakar but little evidence of it in the downtown area. However; there was some evidence of local transmission based on reports of malaria among permanent residents. An entomological evaluation of malaria transmission was conducted from May 2005 to October 2006 in two areas of Dakar. METHODS: Mosquitoes were sampled by human landing collection during 34 nights in seven places in Bel-air area (238 person-nights) and during 24 nights in five places in Ouakam area (120 person-nights). Mosquitoes were identified morphologically and by molecular methods. The Plasmodium falciparum circumsporozoïte indexes were measured by ELISA, and the entomological inoculation rates (EIR) were calculated for both areas. Molecular assessments of pyrethroid knock down resistance (Kdr) and of insensitive acetylcholinesterase resistance were conducted. RESULTS: From May 2005 to October 2006, 4,117 and 797 Anopheles gambiae s.l. respectively were caught in Bel-air and Ouakam. Three members of the complex were present: Anopheles arabiensis (> 98%), Anopheles melas (< 1%) and An. gambiae s.s. molecular form M (< 1%). Infected mosquitoes were caught only during the wintering period between September and November in both places. In 2005 and 2006, annual EIRs were 9,5 and 4, respectively, in Bel-air and 3 and 3, respectively, in Ouakam. The proportion of host-seeking An. gambiae s.l. captured indoors were 17% and 51% in Bel air and Ouakam, respectively. Ace 1 mutations were not identified in both members of the An. gambiae complex. Kdr mutation frequency in An. arabiensis was 12% in Bel-air and 9% in Ouakam. CONCLUSION: Malaria is transmitted in Dakar downtown area. Infected mosquitoes were caught in two subsequent years during the wintering period in two distant quarters of Dakar. These data agree with clinical data from a Senegalese military Hospital of Dakar (Hospital Principal) where most malaria cases occurred between October and December. It was the first detection of An. melas in Dakar.