Molecular epidemiology of hepatitis delta virus in the Western Pacific region.

Background: Hepatitis delta virus (HDV) is a defective RNA virus requiring the presence of the hepatitis B virus (HBV) for the completion of its life cycle. Active replication of HDV can lead to severe hepatitis, and although present worldwide has an irregular geographical distribution, especially in the Asian Pacific region.

Objectives: The aim of this study was to determine the prevalence and molecular epidemiology of HDV isolates in Oceania following the 1998 evaluation of the hepatitis B vaccine program.

Study Design: Sera collected from 184 hepatitis B surface antigen (HBsAg) positive Pacific Islanders living in Micronesia, Polynesia and Melanesia were tested for HDV RNA.

Results: Twenty of 54 patients with chronic hepatitis B (CHB) from Kiribati were positive for serum HDV RNA (37%), whilst sera from patients with CHB from Tonga (59), Fiji (42) and Vanuatu (29) were negative. The mean HDV RNA load for the 20 samples was 7.00log10copies/mL. Phylogenetic analysis revealed that the Kiribati HDV isolates were of genotype 1 and clustered with a previously published isolate from Nauru forming a distinct clade of Pacific HDV. All Micronesian isolates contained a serine at codon 202 of large hepatitis delta antigen (L-HDAg) demonstrating possible relatedness to strains of HDV-1 of African origin.

Conclusions: This study has confirmed endemic HDV infection in Micronesia and identified Kiribati as having amongst the highest prevalence for HDV viraemia in patients with CHB. Further investigations are ongoing into the origins of this unique HDV Pacific strain, and its inter-relationship with HBV.