A new focus of Schistosoma mansoni in the highlands of Burundi

A hitherto unknown focus of Schistosoma mansoni has been discovered and describe around lake Cohoha (alt. 1350 m) in the northeaster of Burundi. The overall prevalence among the lake-shore population is 19%; but the geographical distribution is very focalised with local prevalences ranging from 1% to 51%. Apparently, this is a young focus expanding along the shores of the lake. Young males are by far the most frequently and heavily infected. The intermediate host is probably Biomphalaria stanleyi, but its distinction from B. pfeifferi, the dominating species in the area, is not entirely clear. The snail infection rates are very low. The snail populations show strong fluctuations related to the pollution of the water by harvest wastes. The possibility that this focus will expand to the highlands of Burundi and Rwanda is discussed.