Characterization of five nearly full-length genomes of early HIV type 1 strains in Ruili city: implications for the genesis of CRF07_BC and CRF08_BC circulating in China.

To trace the genesis of HIV-1 CRF07_BC and CRF08_BC, two predominant circulating recombinants among intravenous drug users in China, a retrospective molecular epidemiological investigation (1996-1998) was conducted in Ruili city of Yunnan, where the first AIDS epidemic among IDUs was reported in 1989. Fifty-four HIV-1 env C2V3 sequences were determined and genotyped with 49 subtype B and only 5 subtype C strains. The nearly full-length genome analyses of these five env-based subtype C samples revealed that four of them were actually BC recombinants and only one was pure subtype C. The first identified nonrecombinant HIV-1 subtype C, genetically close to Indian C representatives, provided direct evidence for the hypothesis that subtype C in China was introduced from India. Interestingly, three BC recombinants with subtype B as backbones were identified; one BC recombinant that precisely shared a common subtype B segment (nef region) with CRF07_BC and CRF08_BC was described, which indicated a close evolutionary relationship to these two CRFs. The sequences undoubtedly lead us to a better understanding of the emergence of CRF07_BC and CRF08_BC.