ECOEPIDEMIOLOGY OF MALARIA IN THE RIVER V ALLEY, REPUBLIC-OF-NIGER

The Niger valley is an original ecosystem in the Sahelian belt For mor e than 25 years it has been affected by dryness and rainfall decreased by more than 30 % as compared to the period 1950-960, Moreover he dem ography has sharply increased and the capital town Niamey grew by 10 % a year. The Niger valley including Niamey has about 1 million inhabit ants. Three sires have been selected to study the status oi malaria an d its evolution for the last 30 years: Niamey, Karma 40 km on the N.W. on the river and the nearby fossil valley oi Fatay-Karma. in the sixt ies the malaria vectors were An. gambiae; An. arabiensis et An. funest us. The last species was no more harvested after 1970 because its bree ding places have been destroyed on the combined action oi dryness and human activities. In Niamey, parasite index was very low in the dry se ason but grew by 5 to la times during the rainy season to reach 50 % i n certain corners. The highest plasmodic index (PI) were recorded alon g the river banks where vectors are found ail the year long. it decrea ses in the central part of the city and becomes veri low in some perip heral suburban settlements. This situation is quite different oi most oi the cities oi the area where prevalence decrease from outskirts to city centre. The serology confirms these points. In Karma, along the N iger and despite a perennial transmission, the PI removes low as well as the malaria antibodies, probably because oi the self use of antimal arial drugs by the population. in Fatay-Karma the Pi al 23.9 % after t he rainy season drops to 6 % in the dry one in data prior to 1970 the PI was over 60 %, reaching 89 % in young children of Niamey suburbs. O bviously it has strongly decreased. it is very likely that this is due partly to the disappearance of An. funestus after the drought.