Malaria in the southern sanitary District of Dakar (Senegal) 2. Entomological data.

To complete a parasitological survey entomological prospections were carried out in the southern sanitary District of Dakar, the most urbanized of the city and which includes the city centre and the oldest administrative districts. The prospections took place between lune 1994 and May 1995 in sites 1.5 km apart; and distributed in such a manner that they covered the entire area. On a monthly basis, female Culicidae were collected in each site at night on human volunteers, followed the next day by the collection of early morning residual fauna in 10 bedrooms located in district concessions. For a total of 308 collections at night on human volunteers and from 1,510 rooms for the residual fauna, 22,901 female Culicidae were caught of which 167 anopheles, corresponding to 0.7%, the remaining 98.5% being Culex quinquefasciatus. This was the species that thus explained the mosquito-nuisance of which the inhabitants of the southern District complained during the period of survey. The female anopheles collected belonged to 2 species, An. arabiensis for 97.6 % of those caught and An. pharoensis for 2.4 %. An. arabiensis were very slightly represented in the southern District with a density of aggressive females of 0.26 bite/man/night (B/M/N) and a density per room of 0.05 female. The aggressive populations appeared to be relatively important only at the end of the rainy season (September-October) with an average of 0.65 B/M/N in sites located at the periphery of the district with a maximum of 1.33 B/M/N. The highest density of endophilic females registered at the end of the rainy season was 0.1 and its highest value in a given site was 0.36 female/room. The parturity rate of aggressive females was 43.5% and those collected in houses of 84% with an anthropophilic index of 0.98. None of the dissected An. arabiensis females (77.3% of those collected) was a carrier of Plasmodium sporozoites and the circum-sporozoite antigen was not found. A very weak density of An. arabiensis and absence of plasmodial infection among dissected females favoured the absence of malarial transmission in the southern District for the period considered. However malaria transmission could not be absolutely ruled out given the presence of hematozoa carriers, as was revealed by the longitudinal follow-up of a cohort carried out concurrently with the entomological prospections of whom some were residents having declared permanent residence in the city for over two years. This entomological data explain the results of the afore mentioned parasitological survey which, with a registered plasmodic index of 0.3%, means that the southern District can be considered as non endemic. The area is however exposed to the risk of epidemic malaria following an important proliferation of anopheles, which is always possible after heavy rains and flooding and/or an important immigration of persons coming from regions of high malarial endemicity.