Epidemiiology of Schistosohiasis in Bahir Dar

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Addis Ababa University


Various aspects of the epidemiology of schistosomiasis mansoni were stuoieo for a period of one year at Bahir Dar \~ith the prime o"bj ecti V0 of elucioating the transmission patterns. Parasitological surveys revealed an overall prevalence of 12% among residents of Kebeles 8, 9 and 10. More males ( 17%) than females (8%) were infected ( P.(.O.Ol). The overall prevalence for school children of Dil chibo anO Sertse Dengel were 32% and 45%, respectively. School children yielded high annual incidence at the second survey (February). Malacological findings suggested that Biomphalaria pfeifferi snails peaked in density in September, towards the en6 of the rainy season in Lake Tana ana in January, around the miadle of the dry season at a site on the bank of the River Abay. In September, infected snails were recovered from all collection sites. Schistosome infection also developed in a relatively large number of mice immersed in the month of September. In two series of surveys, the major ~Iater contact activities were identified and it was observed that there were diurnal and seasonal/variations in these activities. The study in general revealed that infection rates depend on age, sel< and geographical location with respect to wat er body. Snail population dynamics and associated schistosomal infection seem to depend on rainfall and associated ecological changes. Incidence studies, malacological findings and sentinel - mouse el<posure results suggest that the main transmission season in Lake Tana is towards the end and after rainy season. Intermittent transmission may also take place throughout the year. Diurnal and seasonal variations in human-water contact behaviours such as playing in \~ater of children, bathing and swimming appear to have epidemiological significance in the transmission of schistosomiasis.