Tracing the Evolution of Hepatitis C Virus in the United States, Japan, and Egypt By Using the Molecular Clock

The molecular clock has been a very powerful tool in looking back at the epidemic spread of HCV infection in the United States (US) and Japan, as well as in Egypt. This analysis estimates that the growth of the US HCV genotype 1a (HCV-1a)-infected population occurred around 1960, at least 30 years later than the widespread introduction of HCV-1b into the Japanese population. In Japan, the estimated effective number of HCV infections indicated a rapid exponential growth in the 1920s among patients with schistosomiasis, which coincides with injection treatment for schistosomiasis since 1921 in previously schistosomiasis-endemic areas. In Egypt, the spread of HCV-4a would have increased exponentially during the 1940s through 1980, which was also consistent with the duration of intravenous antimony campaigns for the treatment of shistosomiasis in that country. The implications are that Japan has set the model for HCV-related HCC, and that the high HCC incidence in Japan might be replicated by the rest of the world as their HCV-infected population ages and the duration of HCV infection approaches that currently observed in Japan.