THE IMPACT OF RICE FIELDS ON THE TRANSMISSION OF MALARIA IN BOUAKE, COTE-DIVOIRE

This study evaluates the impact of rice fields in the city of Bouake o n anopheline fauna and malaria transmission. The Anopheles species rep resents between 11.4 to 39.2% of mosquitoes in the districts with rice fields and 5.2 to 47.8% in lowland districts with market-gardening. A n. gambiae constitutes more than 98% of anopheline population in the c ity. In the lowland districts with market-gardening, biting rates of A n. gambiae varied from 3650 to 6935 bites per man per year. Seasonal v ariations were correlated with rainfall. The mean annual parturity rat e was 72% and the mean sporozoitic index 2%. Malaria transmission star ted at the begining of the rainy season and attained its height during the second half of this season. Depending on the district, inhabitant s were infected with 78 to 134 bites per year. The mean biting rate of An. gambiae in the districts with rice fields varied from 4745 to 226 30 bites per man per year. Seasonal variations were not correlated wit h rainfall, but with the growth of rice and the two annual cycles of r ice cultivation. The parturity rates of the population of An. gambiae were low (46.2% to 57.2%), especially after rice transplantation. The mean infection rates were between 0.7 and 1.0%. The transmission perio d covered 7 to 11 months depending on the district with two annual pea ks observed at the end of rice cultivation. inhabitants were infected with 44 to 155 bites per year. Rice fields in Bouake do not seem notab ly to have modified malaria transmission in the city.