Hepatitis delta virus genotype IIb predominates in an endemic area, Okinawa, Japan

Hepatitis delta virus (HDV) infection is relatively common in the Miyako Islands, Okinawa, Japan, where the infection has been reported to be associated with low pathogenicity. HDV RNA extracted from each of 6 patients with HDV-related chronic liver disease living in the islands was amplified by reverse transcription-polymerase chain reaction and examined genetically to determine the HDV genotype. All isolates from the 6 patients were classified as genotype II by the neighbor-joining method. However, these isolates had relatively low homology (75-81%) to the HDV genotype II isolate reported from Japan, and showed relatively high identity (83-95%) to the novel genotype II isolate (HDV genotype IIb) recently reported from Taiwan. Phylogenetic analysis showed that the 6 isolates form a novel group within HDV genotype II. Furthermore, there was notable variation in sequence among the 6 isolates compared with the relatively close clustering of HDV isolates within limited areas (e.g., United States, Archangelos, Turkey, Albania, Peru). HDV genotype II in the Miyako Islands is therefore unique, and HDV infection may have been introduced at a relatively early time in this area.