Phylogeny of African complete genomes reveals a West African genotype A subtype of hepatitis B virus and relatedness between Somali and Asian A1 sequences.

Hepatitis B virus (HBV) is a major cause worldwide of liver disease, including hepatocellular carcinoma. There are eight known genotypes (A-H), of which genotype A has been divided into two subtypes: A2, prevalent in Europe, and A1, which is prevalent in sub-Saharan Africa, but also occurs in southern Asia. In this study, which includes 14 new complete genomes of non-European genotype A HBV, it was found that West African strains seem to constitute a new subgroup, A3. The high degree of genetic diversity within Africa indicates that genotype A originates from Africa. Based on a 2 % genetic distance between Asian and Somali sequences, it seems that the A1 subtype has spread from East Africa to southern Asia during the last 1000-2000 years. Moreover, it is proposed here that the A2 subtype originates from southern Africa and was imported to Europe around 500 years ago or later. The finding of T-1809/1812 close to the precore start codon and T-1862 and A-1888 in the precore region in HBV e antigen-positive children with signs of a mimimal immune response indicates that these substitutions are stable variants, rather than mutations emerging during infection in individual carriers.