Introduction:
Hepatitis B was first described in an Indigenous Australian in 1965. Decades later chronic hepatitis B (CHB) prevalence continues to be high at 1-14% in the Northern Territory (NT). Universal vaccination (vaccine strain sub-genotype A2 serotype adw2) has been practiced in the NT since 1990 however several small studies raise concerns about its effectiveness in this population.
Methods:
Blood specimens and clinical details from Indigenous adults infected with HBV and who were born and raised in the NT were obtained. HBV full genome sequences were determined from isolates with sufficient HBV DNA by polymerase chain reaction. Phylogenetic and recombination analysis was then performed.
Results:
Serum samples were obtained from 65 HBsAg positive individuals of whom 35 had sufficient viral load to obtain a full genome sequence. All samples were sub-genotype C4, serotype ayw3. Recombination analysis revealed a ~600 base pair section of C4 that showed greater similarity to genotype J as opposed to other C sub-genotypes. This recombined region encompasses most of the small surface antigen gene of the hepatitis B virus. Molecular markers consistent with an aggressive phenotype were identified.
Conclusion:
C4 is the exclusive sub-genotype in the NT Indigenous population and has only twice previously been described in two Indigenous individuals from Queensland. This is a recombinant virus with a different serotype to the currently used vaccine strain and may provide a virological explanation for the observed concerns about vaccine effectiveness in this population.