Biological characteristics and control of intermediate snail host of Schistosoma japonicum.

Except for imported cases, we have had no new Schistosoma japonicum infection in Japan since 1977. But there are still two habitats of the intermediate snail host: Oncomelania nosophora in the previous endemic areas of Kofu Basin and Obitsu. O. nosophora from Kofu Basin and Obitsu are susceptible to Chinese and Philippine strains of S. japonicum. The number of immigrants from current endemic areas in China or the Philippines is increasing. In order to prevent re-emerging of S. japonicum infections in Japan, we should continue monitoring on those existing snail hosts and investigate an adequate quarantine system. In Japan, elimination of schistosomiasis has been mainly accomplished by control of the snail host. As measures of snail control, cement-lining of ditches and chemical mollusciciding were most effective in Japan. But the cost of this joint program is too expensive compared with health budget in almost developing countries. In endemic areas of Japan, land reformation from paddy field to fruit farm was also effective. The intermediate snail host in the Philippines, Oncomelania quadrasi is much more aquatic than O. nosophora. For control of O. quadrasi, small drainage of the water and land reclamation from swampy field to rice-field were effective. Based on biological characteristics of Oncomelania spp., we can modify the past successful snail control program in Japan to be adapted ecologically and economically to each endemic area of developing countries.