MALARIA IN THE SAHELIAN AREA OF SENEGAL .1. ENTOMOLOGICAL DATA

An 18 months longitudinal survey on the entomological aspects of the t ransmission of malaria has been carried out in a village practising ri ce field irrigation and in another village with traditional rain water agriculture. Both are located in the Sahelian area of the Senegal riv er central valley, in Senegal. The study is based on mosquito samples caught on human baits. The vectors A. arabiensis and A. gambiae could be found all year long in the village with rice field irrigation, but only during the rainy season in the other village distant from the ric e field area. The average agressive density decreases with the remoten ess from the rice field area. From 16 bites/man/night (BMN) in the ric e field area, it decreases to 7 BMN at 500 m and to 1 BMN at 5 km dist ance. The malaria transmission rate is weak and was not perceptible in the villages located far away from the rice field area. In the villag e close to the irrigated rice field, only one infected A. gambiae s.l. has been caught during the period of study. Physiological age is high er in the rice field area, but the anthropophilic index is lower. The different parameters involved in malaria transmission show important s easonal and yearly variations. Irrigation has, on the whole, increased mosquito population densities and particularly that of A. gambiae s.l ., but malaria transmission does not seem tot be influenced by this in crease.