Hepatitis E virus subtype 3f strains isolated from Japanese hepatitis patients with no history of travel to endemic areas – The origin analyzed by molecular evolution

Highlights: • Rare cases of acute hepatitis E infected by HEV-3f strains in Japan. • The cases had no history of travel to endemic areas of HEV-3f strains. • The origin of the HEV-3f strains were analyzed by molecular evolution. • The result indicated recent inflow of multiple HEV-3f strains from Europe to Japan. • Importation of pork products might be a source of HEV-3f in Japan. Hepatitis E virus subtype 3f (HEV-3f) strains are usually isolated in Europe and Thailand. Recently, HEV-3f strains were detected from six acute hepatitis E patients in Japan, none of whom had a history of travel to endemic areas. We inferred the origin and transmission route of the six HEV-3f strains. A time-scaled phylogenetic tree of the six strains with reference strains was constructed using a Bayesian statistical inference framework. The time-scaled tree indicated that the six strains independently derived from similar European strains between 2008 and 2014. The pattern suggested recent inflow of multiple HEV-3f strains from Europe to Japan. Japan imports a substantial amount of pork from European countries every year. The emergence of acute hepatitis cases caused by HEV-3f strains in Japan, in patients with no history of travel abroad, might be influenced by the increased opportunities to consume pork products imported from European countries.