Molecular analysis of hepatitis D virus infection in Miyako Island, a small Japanese island

The present investigation attempted to determine the exact prevalence of hepatitis D virus (HDV) infection among inhabitants of Miyako Island (a remote island in the Okinawa Prefecture) and the molecular characteristics of the HDV genome that was isolated. Among the 4728 inhabitants, 375 (7.9%) were hepatitis B surface antigen (HBsAg) positive. Antibody to HDV (anti-HDV) was present in 32 (8.5%) of these 375 subjects, and liver function tests were normal in most subjects. The presence of HDV RNA was analysed by nested polymerase chain reaction (PCR). Thirteen out of the 32 anti-HDV antibody-positive subjects were HDV RNA positive. Thus, 3.5% of HBsAg-positive subjects on Miyako Island were HDV RNA positive. Among the HDV RNA-positive subjects, liver function tests were within normal limits or were mildly abnormal. Nucleotide sequence analysis revealed that the HDV genomes on Miyako Island were similar to the Japanese and Taiwan isolates of HDV genotype II. Taiwan is geographically close to Miyako Island. Even though the races are different, a geographical factor was revealed to be significant with regard to HDV infection, which was spread in a closed environment.