TRANSMISSION OF MALARIA AROUND NIAKHAR, SENGAL

The anopheline bioecology and the malaria transmission were studied fr om January to December 1995 in three villages of the sahelian rural ar ea of Niakhar, Senegal. This area of 29 000 inhabitants, has been for several decades, a regional observatory for population and health. The three methods used fur collecting mosquitoes were the collection at l arval stages, the all night human biting collection, and the pyrethrum spray catch in houses during afternoons. The anophelines collected we re, by numerical importance: Anopheles arabiensis, An. rufipes, An. ga mbine, An. pharoensis, An. funestus and An. coustani. In the An. gambi ae complex, An. arabiensis represented 97% of man biting females and 9 8% of half gravid resting females (difference not significant); the ot her reminding species of this complex was always An. gambiae. These tw o species belonging to the An. gambine complex were responsible for th e totality of the transmission. The anthropophilic index, obtained fro m half gravid indoor resting An. gambiae s.l., was 83%. The annual bit ing rate of An. gambiae s.l. varied from 512 to 1558 bites per man per night, depending on the villages. Vectors were observed all pear long but their densities were low during the dry season. Vector population presented a notable increase due to the rains, with a maximum of abou t 10 bites per man per night in September or at the beginning of Octob er; during September the biting rate represented 48% of the annual bit ing rare. The sporozoitic index of An. gambiae s.l., obtained by ELISA revealing the circumsporozoite protein, was 1.6% for human biting fem ales and 1.8% for half-gravid resting females (difference not signific ant). Plasmodium falciparum was the only plasmodial species observed a mong infected anophelines. The annual transmission in the two villages representative of the Niakhar area were 9 and 12 bites of infected an ophelines per mail. occurring mainly from August to October In the thi rd village, not representative of the area regarding permanent breedin g places, the transmission was 26 bites of infected anopheline per man per year. These results were discussed in the Senegambian and sahelia n contexts.