ケニア国タベタ地区での淡水産貝類は以下の8属11種である。即ちBiomphalaria pfeifferi(Krauss)，B. sudanica (Martens)，Bulinus globosus (Morelet)，B. tropicus (Krauss)，B.forskalii (Ehrenberg)，以上5種は住血吸虫との関係種，Lymnea natalensis (Krauss)，Ceratophallus natalensis(Krauss)，Segmentorbis angustus (Jickeli)，Gyraulus costulatus (Krauss)，Bellamya unicolor (Olivier)，Melanoides tuberculata (Muller)である。B. pfeifferiはLumi川と灌漑用溝に， B. sudanicaはJipe湖畔に，それぞれの多数の棲息をみたが，マンソン住血吸虫の自然感染はB. pfeifferiのみに見られた。B.globosusは灌漑用溝のみに多数棲息し，B. tropicusは灌漑用溝とJipe湖畔に，B. forskaliiは少数ながらあらゆる水系に見出された。ビルハルツ住血吸虫の自然感染はB. globosusのみに見出され，その貝の棲息数が多いと約10%の高い感染率が常時認められた。一方これらの実験感染では，B. pfeifferiには3隻のミラシジウムで，B. sudanicaには5隻のそれで100%感染が成立し，両種ともマンソン住血吸虫の好適な中間宿主であることがわかった。B. globosusは1.5～8.5mmの若い貝は5隻のミラシジウムで100%感染が成立し，11～12mmの成貝では20隻以上のミラシジウムが必要である。ビルハルツ住血吸虫の好適な中間宿主であることがわかった。以上からタベタ地区でのマンソン住血吸虫症，ピノレハルツ住血吸虫症の媒介中間宿主として，前者にはB. pfeifferiとB. sudanicaが，後者にはB.globosusが主な役割を演じていることが推測される。The present study was carried out in the permanent water streams of Lumi River, Irrigation Furrow and Lake Jipe in the Taveta area, Coast Province, Kenya during the dry seasons of 1974 and 1975, and the experimental infection was made at laboratory in Japan. Freshwater snails collected in the Taveta area were as follows: Biomphalaria pfeifferi (Krauss), B. sudanica (Martens), Bulinus globosus (Morelet), B. tropicus (Krauss), B. forskalii (Ehrenberg), Lymnea natalensis (Krauss), Ceratophallus natalensis (Krauss), Segmentorbis angustus (Jickeli), Gyraulus costulatus (Krauss), Bellamya unicolor (Olivier) and Melanoides tuberculata (Muller). B. pfeifferi was commonly found in river and irrigation canal, whereas B. sudanica only in lake. Natural infection of Schistosoma mansoni was found in B. pfeifferi, but not in B. sudanica. Both the two species were experimentally proved to be suitable intermediate snail hosts of S. mansoni. Therefore it was indicated that B. pfeifferi is the host snail of S. mansoni in the endemic area along river and irrigation canal while B. sudanica is suspected of playing the role in the transmission of S. mansoni in lakeshore. B. globosus was commonly found in irrigation canal. Around 10 per cent of the snails proved to be naturally infected with S. haematobium on the conditions that many snails occurred. This snail was also experimentally proved to be susceptible to S. haematobium. B. forskalii was widespread, but the snail density seemed to be low. B. tropicus is well known as the not-intermediate snail host of S. haematobium. Therefore there might be a possibility to contribute only by B. globosus to the transmission of S. haematobium in this area
