The GB viruses Fig. 3. Helicase and RdRp phylogenetic trees of selected members of the family Flaviviridae. NJ analyses were performed on the conserved motifs aligned as shown in Supplementary Figs S1 and S2, and their intervening sequences. A distance scale in amino acid substitutions per position is shown. Proposal to classify ‘GB’ viruses We propose that GBV-A, GBV-A-like agents, GBV-C/HGV and GBV-D should be classified together within a new genus (Pegivirus) within the family Flaviviridae. This is based on their phylogenetic relationships, genome struc- ture, ability to persist in vivo and apparent lack of pathogenicity. This designation indicates that these viruses cause persistent infection (Pe), and provides historical recognition of the relationship with the ‘GB’ agents and hepatitis G virus (g). We propose to rename GBV-A as simian pegivirus (SPgV). This indicates the primate host range (S) and through the genus designation provides historical reference to their relationship to the ‘GB’ serum inoculation (Pg). The host species for different GBV-A variants will be identified by subscript suffixes. For example, SPgV will include SPgVmys, SPgVtri, SPgVlab and SPgVjac. We propose to rename GBV-C/HGV as human pegivirus (HPgV) for similar reasons, and genotypes will be identified by subscript suffixes. The chimpanzee GBV-C variants would be called SPgVcpz to reflect its simian host. The recently reported GBV-D virus found in fruit bats would be described as Bat PgV (BPgV). Should related BPgV isolates be identified in different species, the host species of the current bat isolate will be designated by the http://vir.sgmjournals.org subscript suffix (pgi) for the current virus identified in the species P. giganteus, and the new related viruses will be identified by their host species. This nomenclature avoids the suggestion that these viruses either cause hepatitis or were derived from the surgeon ‘GB’. We support the proposal to classify GBV-B as a second species within the genus Hepacivirus, as this virus causes hepatitis in experimentally infected tamarins, thus it was the true GB-agent (Thiel et al., 2005). Although the surgeon GB would not have been infected with this virus, it is the agent responsible for the hepatitis observed in tamarins used in serial passage studies. Since, under the proposed nomenclature, there will not be any other ‘GB’ viruses, we propose to rename GBV-B as GB virus (GBV). Although the ‘GB’ serum was associated with hepatitis following inoculation into tamarins, the specific agent(s) responsible for the hepatitis remain unknown and the reported hepatitis may simply relate to the relatively common finding of non-specific enzyme elevation. A summary of the classification proposal is shown in Fig. 4. Our proposal to rename GBV-A, GBV-C/HGV and GBV-D viruses and to classify them within a new genus (Pegivirus) will be submitted to the International Committee on 241