Phylogenetic analysis of human herpesvirus-8 in South Africa and identification of a novel subgroup.

The incidence of Kaposi's sarcoma in South Africa is increasing in parallel with the human immunodeficiency virus type 1 epidemic. An 804 bp region in the ORF75 gene of 40 human herpesvirus-8 (HHV-8) isolates from South Africa was sequenced and the phylogenetic relationships were compared to published sequences. Nineteen strains clustered with subgroup B and 11 with subgroup A; however, the bootstrap values supporting these subgroups were not significant. Three strains grouped significantly with the C subgroup, while eight sequences did not cluster with any of the previously classified subgroups and were termed novel (N). The N subgroup differed from the A, B and C subgroups by DNA distances of 4.8, 4.2 and 4.5%, respectively, although within the N subgroup there was only 0.4% variation. The inclusion of this subgroup increased the number of previously described subgroup-specific polymorphisms from 17 to 47 over an 804 bp region. There was sufficient inter-subgroup genetic diversity for a single-strand conformational polymorphism assay to be used to identify them rapidly. Thus, based on analysis of the ORF75 gene, a unique HHV-8 subgroup, termed N, is present in South Africa, which accounts for 20% of circulating strains. Further studies are required to determine the degree of genetic divergence, distribution and pathogenic potential of this novel subgroup.