Evidence for widespread infection of hepatitis E virus among wild rats in Japan

Sporadic cases of hepatitis E have been reported in industrialized countries, including Japan. The source of hepatitis E virus (HEV) in these patients is unknown, although zoonotic transmission has been suggested. To investigate whether or not rodents might be a reservoir of HEV, we conducted an epidemiological survey for the antibody to a recombinant capsid protein of HEV using serum samples from wild rodents in Japan. One hundred and fourteen of 362 (31.5%) Norway rats (Rattus norvegicus) and 12 of 90 (13.3%) black rats (Rattus rattus) were positive for anti-HEV IgG. In contrast, all of the sera from 55 mice were negative for anti-HEV IgG. The rate of antibody positivity increased with weight among Norway rats. Seropositive rats were found in all five districts surveyed in this study, but the prevalence of anti-HEV IgG in wild rats differed among these prefectures. Despite the fact that Japan is a non-endemic country of hepatitis E, widespread infection of HEV was observed among wild rats in Japan. Our results suggested that HEV or a closely related virus is circulating among wild rats in Japan.