Changes in the habitat of Oncomelania hupensis nosophora, the intermediate host snail of Schistosoma japonicum, along the Obitsu River basin, Chiba Prefecture, Japan

Abstract

Oncomelania hupensis nosophora (Ohn) is the intermediate snail host of Schistosoma japonicum (Trematoda; Schistosomatidae) (Sj) in Japan. The last domestic schistosomiasis infection in Japan has been thought to occur in Yamanashi Prefecture in 1977. In 1985, the intermediate host snail was isolated from paddy fields along the Obitsu River basin in Chiba Prefecture, Japan. At that time, schistosomiasis was assumed to become a past disease in this area. Thus, activities to exterminate Ohn or annual screening programs of residents in this area had not been conducted. Indeed, this disease represents a neglected endemic disease in Japan. This report describes the epidemiological history of the disease from various approaches including clinical information, philological study, interview surveys, snail collection surveys, and changes in land use and environments using geographic information systems. The assumption of disease elimination was based on the lack of reports of new infection for more than 30 years, environmental modifications, and almost no snail infestation from 2012 onward in known habitats. We concluded that continuous monitoring of the snails is not necessary in the studied area, while a certain level of attention to redistribution of the snail from hidden habitats may be required.