Bilharziasis control in pump schemes near Khartoum, Sudan, and an evaluation of the efficacy of chemical and mechanical barriers.

Agricultural schemes irrigated by pumps are of significant importance in the spread of bilharziasis in the Sudan. On the basis of detailed pre-control studies and of post-control evaluation in some of these schemes near Khartoum, a procedure is recommended by which it is thought that satisfactory results could be obtained.Although use of a "chemical barrier" (i.e., the continuous application of a concentration of 0.125 p.p.m. of copper sulfate as a maintenance dose) has apparently been successful in reducing the snail population in the Gezira irrigation scheme in the Sudan, where it was initiated, it has not yielded satisfactory results in certain other countries. An evaluation of this method and of mechanical barriers has been attempted in the studies reported here and it was found that the canals remained suitable habitats for snails introduced downstream from the site of application of the maintenance dose. The principle of continuous application of low concentrations of molluscicides is probably sound and might be effective; further investigations are, however, necessary to improve the method, and to provide further data on the possibility of a residual effect resulting from continuous application.