Oncomelania nosophora in Kofu basin,Yamanashi Prefecture, Japan

Abstract

Epidemiological records were not reported before the discovery of the causative agent Schistosoma japonicum. The first comprehensive epidemiological survey was conducted in 1911. Out of 69,131 patients, 7,893 were recorded to have a high infection rate of 11.4%. Countermeasures for snail control since 1909 when the intermediate snail host was discovered are historically divided into three stages. The first stage was from 1913 when the life history of the parasite was elucidated to the end of the World War II in 1945. In 1916, Yamanashi Prefecture provided funds for the systematic control of the disease including snail control. In 1924, molluscicides of lime were introduced. In 1932, the Japanese government created a law to support parasite control. The second stage was from 1946 after the end of the World War II to eradication in 1996. During occupancy, the United States army started surveys and instructional programs. Na-PCP was introduced and used until 1971 when it was incriminated as a water pollution agent. Starting in 1950, cementing of rice paddy ditches was shown effective so an official fund of 11 billion yen was provided until 1985. In 1996 Yamanashi Prefecture finally declared the area safe with cessation of the epidemic. The third stage was from 1997 when the disease was not reported anymore and vigilant activities continue to examine possible infections from the snails till date. Now the snail survives and even proliferates in the Kofu Basin without infection.