Research Articles

Epidemiologic study of the relationship between schistosomiasis due to Schistosoma japonicum and liver cancer/cirrhosis

In Yamanashi Prefecture, one of the former areas in Japan endemic for Schistosoma japonicum, there have been no cases of schistosomiasis since 1978. We attempted to find out in this study whether there was still a chronic effect of schistosomiasis, e.g., liver cancer or liver cirrhosis present in this region. The subjects studied were the population in Yamanashi Prefecture from 1973 through 1992. We divided the population into residents in an area endemic for schistosomiasis and those in a nonendemic area. We calculated the standardized mortality ratios (SMRs) for liver cancer and liver cirrhosis in both areas. The schistosome egg-positive rate of liver cancer and liver cirrhosis specimens from the patients in these two endemic areas was also calculated. Male SMRs for liver cancer in the endemic area were 188.5% in 1985 and 188.0% in 1990. Even today, many years after the last case of schistosomiasis, schistosome eggs can be found in the livers of deceased liver cancer and cirrhosis patients. The chronic effect of S. japonicum could contribute to the current high mortality rate for liver cancer in the endemic area, although we need to consider the other etiologic factors of liver cancer, e.g., hepatitis B virus, hepatitis C virus, and alcohol intake.