To know the reality of hepatitis E virus (HEV) infections in Japan, quite obscure until a few years ago, we have collected a total of 254 human cases of HEV infection, and analyzed for demographic, epidemiological, and virological characteristics. As a result, we now know [i] HEV has penetrated nationwide from Hokkaido to Okinawa; [ii] hepatitis E is a disease of middle-aged people (approx. 50 years old in average) with a predominance of male over female (approx. 3.5 vs 1); [iii] HEV strains of genotype 3 and 4 are autochthonous in Japan, but the latter is present almost exclusively in Hokkaido; [iv] the older the age the severer the disease; [v] HEV genotype 4 is associated with more obvious and severer clinical manifestations than genotype 3; [vi] no seasonality in its incidence; and [vii] transmission routes remain obscure in most cases (approx. 60%), whereas about 30%, 8%, and 2% are ascribable to zoonotic food-borne transmission, imported infection, and via blood transfusion, respectively.
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