Epidemiological studies on Schistosoma bovis in Iringa Region, Tanzania

Various aspects of the epidemiology of Schistosoma bovis were studied over a one-year period in Iringa Region, Tanzania. An abattoir survey revealed an overall prevalence rate of 30.8% in cattle and 3.8% in goats in the area, and field studies on two dairy farms both providing good opportunities for schistosome transmission provided information concerning the transmission ecology of S. bovis in relation to different types of grazing and water supply. The traditional management system on one farm with a large number of cattle utilizing a limited water resource highly suitable for sustaining populations of the snail host Bulinus africanus resulted in intensive transmission as evidenced by uptake of massive infections in calves and development of resistance to S. bovis challenge in dairy cows. On another farm, appropriate management comprising watering of cattle at a B. africanus-free pond provided the background for less intensive transmission in that transmission risk was confined to occasional contact with water contact sites of secondary importance. Besides, the transmission pattern as regards intensity and seasonality was affected markedly by the geographical and seasonal distribution of the host snail B. africanus. Thus, transmission in canals and temporary ponds was limited mainly to the dry season and the end of the rainy season, respectively, while transmission in permanent ponds occurred intermittently throughout at least most of the year. It is concluded that prevention of severe loss of productivity in domestic ruminants due to schistosome infections should be possible using strategic management procedures provided that essential information is available concerning the pattern of transmission in the particular area.