Hepatitis B and D in the Pacific Islands of Kiribati

Background: Historical reports indicate that hepatitis B and hepatitis D are highly endemic in the Pacific Island of Kiribati but current levels are unknown. Objectives. To determine current prevalence of HBV and HDV in Kiribati, characterize the strains in both mono-infection and co-infection and assess individuals for antiviral therapy. Study design: Sera obtained from 219 patients were screened for HBsAg, HBeAg, HBV DNA, anti-HD, and HDV RNA. 61 HBV isolates were sequenced for genotype, phylogenetic analysis and detection of pre-core and basal core promoter mutations. 82 HDV isolates were also sequenced. Results: 55.7 % HBsAg positive samples had antibodies to HDV and 73.2 % had detectable HDV RNA, indicating that 40.8 % HBsAg-positive individuals had current HBV/HDV co-infection. There were 42 co-infected males and 40 females; the youngest individual was a 4 year-old boy. HBV isolates were genotype D4, and HDV strains formed a distinct Pacific clade of genotype 1. Undetectable HBV DNA loads were statistically more frequent in the co-infected sub-population (p < 0.0001). Basal core promoter and pre-core mutations were present in both mono and co-infection. Conclusion: Kiribati has one of the highest HBV/HDV co-infection rates in the world. The epidemiology of coinfection in this population was unusual with males and females equally represented and the presence of coinfection in a 4 year old child suggesting neonatal or early horizontal transmission, which is extremely rare. Coinfection with HDV resulted in statistically significant suppression of HBV DNA levels. The HDV strain identified in Kiribati was unique to the Pacific Islands.