Focusing of Schistosoma haematobium transmission in irrigated perimeters of the Niger valley (Niger):: importance of malacological factors

Background. - Currently, the control of urinary schistosomiasis is mostly based on mass treatment. Characterization of Schistosoma haematobium transmission could lead to adding new methods to the control strategy. Methods. - We carried out malacological and cercariometrical surveys in irrigated perimeters of the Niger River valley. A semi-monthly follow-up was performed in three main sites of human-water contact in a village located at the border of the irrigated perimeter. Bulinids were collected during 20 min; after identification based on the shell morphology, their parasites were characterized by isoelectrofocalisation. The cercariometrical technique by differential filtration was used to evaluate the density of cercariae in every site with two 20 litres samples of water collected at various periods of the day (9, 12, 15 and 18 h). Results. - In the arm of the river, the cercariometry never showed cercariae whereas only some Bulinus truncatus, all negative, were collected. In the channels, B. truncatus and B. globosus were observed and highest density was found during the dry season. Only B. truncatus was naturally infested. Homozygote 1313 phenotype (characteristic of S. haematobium) was observed in all positive molluscs. Using cercariometry, more than two third of cercariae were collected at 3:00 PM. Conclusion. - Transmission of S. haematobium was primarily focused in the irrigating channels during the dry hot season at the beginning of afternoon. These results should lead to improve the output of S. haematobium control methods within irrigated areas. (C) 2008 Elsevier Masson SAS. Tous droits reserves.