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.

Antibody response against saliva antigens of Anopheles gambiae and Aedes aegypti in travellers in tropical Africa.

Exposure to vectors of infectious diseases has been associated with antibody responses against salivary antigens of arthropods among people living in endemic areas. This immune response has been proposed as a surrogate marker of exposure to vectors appropriate for evaluating the protective efficacy of antivectorial devices. The existence and potential use of such antibody responses in travellers transiently exposed to Plasmodium or arbovirus vectors in tropical areas has never been investigated. The IgM and IgG antibody responses of 88 French soldiers against the saliva of Anopheles gambiae and Aedes aegypti were evaluated before and after a 5-month journey in tropical Africa. Antibody responses against Anopheles and Aedes saliva increased significantly in 41% and 15% of the individuals, respectively, and appeared to be specific to the mosquito genus. A proteomic and immunoproteomic analysis of anopheles and Aedes saliva allowed for the identification of some antigens that were recognized by most of the exposed individuals. These results suggest that antibody responses to the saliva of mosquitoes could be considered as specific surrogate markers of exposure of travellers to mosquito vectors that transmit arthropod borne infections.

Antibody responses to several malaria pre-erythrocytic antigens as a marker of malaria exposure among travelers.

Protective devices against vectors are used by travelers in malaria-endemic areas but their efficacy for protection against mosquitoes has rarely been evaluated. The level of exposure to malaria transmission of 205 soldiers deployed in Africa and the efficacy of their anti-vector prophylaxis was evaluated by comparison of their IgM and IgG responses against five pre-erythrocytic Plasmodium falciparum antigens (circumsporozoite protein, sporozoite threonine- and asparagine-rich protein, sporozoite- and liver-stage antigen, liver stage antigen 1, and SR11.1) before and at the end of their deployment, and three months after returning to France for 106 of these soldiers. The immune responses increased significantly during the mission in 35% (95% confidence interval = 28-42%) of the individuals. The permanent use of insecticide-treated bed nets and long-sleeve battle dress at night were associated with protective efficacy. The analysis of these antibody responses was sensitive enough to evaluate exposure to malaria transmission and the efficacy of anti-vector devices in travelers using antimalarial chemoprophylaxis.