GENETIC RELATEDNESS OF HEPATITIS-B VIRAL STRAINS OF DIVERSE GEOGRAPHICAL ORIGIN AND NATURAL VARIATIONS IN THE PRIMARY STRUCTURE OF THE SURFACE-ANTIGEN

A 681 nucleotide fragment of the hepatitis B virus (HBV) genome was se quenced that corresponded to the complete gene for hepatitis B surface antigen (HBsAg) in 80 HBsAg- and hepatitis B e antigen (HBeAg)-positi ve sera of diverse geographical origins. These and 42 previously publi shed HBV sequences within the S gene were used for th e construction o f a dendrogram. In this comparison, each of the 122 HBsAg genes was fo und to be related to one or other of the six previously identified gen omic groups of HBV, A to F. The HBV strains within each genomic group showed a characteristic geographical distribution. Group A genomes wer e represented by 23 strains mainly originating in northern Europe and sub-Saharan Africa. The group B and C genomes, represented by 17 and 2 8 strains respectively, were confined to populations with origins in e astern Asia and the Far East. The group D genomes, represented by 38 s trains, were found worldwide, but were the predominant strains in the Mediterranean area, the Near and Middle East, and in south Asia. Group E genomes, represented by nine strains, were indigenous to western su b-Saharan Africa as far south as Angola. There were indications that t he F group, made up of six strains, represented the genomic group of H BV among populations with origins in the New World. Thus, HBV has dive rged into genomic groups according to the distribution of mankind in t he different continents. As well as giving information on the genetic relationship of HBV strains of different geographical origin, this stu dy also provides information on the primary structure of HBsAg in diff erent regions of the world. Such data might prove valuable in explaini ng the reported failures to obtain protection with current HBV vaccine s.