Molecular evolutionary analyses implicate injection treatment for schistosomiasis in the initial hepatitis C epidemics in Japan

Abstract

Background/aims: The mortality due to hepatocellular carcinoma (HCC) has ranged widely in various areas of Japan since 30 years ago and the incidence was particularly high in once Schistosoma japonicum (Sj)-endemic areas. Our aim was to estimate the spread time of hepatitis C virus (HCV) infection in the past with possible relevance to a higher incidence of HCC in once Sj-endemic than Sj-nonendemic areas.

Methods: During 2001, 131 strains of HCV-1b were obtained from patients in three previously Sj-endemic areas, as well as Sj-nonendemic areas in Japan and a cross-sectional study was conducted on them with molecular evolutionary analyses.

Results: A phylogenetic tree reconstructed on HCV-1b sequences in the NS5B region disclosed 2 independent clusters for Sj-positive and -negative groups with a high bootstrap value. The estimated effective number of HCV-infections indicated a transition from quiescence to rapid exponential growth in the 1920s among patients with schistosomiasis, which is 20 years earlier than that among patients without schistosomiasis.

Conclusions: The estimated spread time in previously Sj-endemic areas in Japan coincides with injection treatment for Sj since 1921. A high incidence of HCC there would be attributed to a long duration of HCV infection since 1920s.