Parasitological view of urinary schistosomiasis of the Sourou hydroagricultural system in Burkina Faso.

In the Sourou area of Burkina Faso, parasitological and malacological surve ys of urinary schistosomiasis have been carried out in the constructed site s of Guedougou, Niasan and Debe dating respectively from 1967, 1986 and 199 6. The investigations covered also the traditional villages of Lan-fiera, D i, Poro, Tiao and Mara situated in the middle of the hydroagricultural plan ning for the first, very close to the lake for the second and about twenty kilometres distant for the three last. These towns represent the main sites in the Sourou area. The results of the parasitological surveys showed that urinary schistosomia sis was present in all sites. The levels of prevalence varied considerably: 70,3% in Guiedougou, 40,8% in Niassan, 8,5% in Debe in the irrigated zone, 55,6% in Lanfiera, 56,8% in Di, 13,2% in Poro, 83,3% in Tiao and 64,7% in Mara. Concerning the malacological investigation, two species (Bulinus senegalens is and B. truncatus) were shown to be intermediate hosts of Schistosoma hae matobium. The first was endemic to the area while the second was compatible with S. haerratobium from the Sourou and other zones. Compared to the resu lts of earlier investigations, the endemic had worsened with differences ac cording to sites. This disparity of prevalence levels which has already bee n observed in other hydroagricultural area results from many factors. among which the impact of irrigation activities, the aquatic biotope system (irr igation canals, natural lake, pools and temporary rivers) and the type of c ontact of human communities with water rank high. Schistosomiasis expansion is amplified by the intermediate host dynamics and the introduction of new schistosomes carried by the new workers arriving from all over the country , In these conditions, in order to reduce rapidly prevalence levels, preventi ve measures should be centred on chemotherapy for the population. The treat ment should be administred during a period of weak intermediate host densit y and be directed towards in-coming workers. Such an approach should be abl e to check the spread of schistosomiasis naturally occurring with the irrig ation of new sites.