1: Service de neurovirologie, CEA, France; 2: CIRMF, Gabon; 3: Institut Pasteur, France; 4: Centre Pasteur du Cameroun; 5: Zoology Dept., Oxford University, UK.

Introduction: Up until now, three HIV-1 lineages (groups M, N and O) are known. Studies have shown a close relationship between SIVcpz from common chimpanzees (subspecies Pan troglodytes troglodytes) and HIV-1 group N. However, only three SIVcpz (P.t.t.) strains (GAB, US and Cam3) have been fully characterized. These sequences, in association with the full-length sequence of HIV-1 group N YBF30, support the hypothesis of transmission of SIVcpz to humans. Objective: To study the group N epidemiology, and to better define the HIV-1/SIVcpz relationship. New group N and SIVcpz strains were derived and phylogenetic analysis performed. Methods: 5464 Human HIV-1 positive samples collected in Cameroon (1997-99) were tested using a group M, O, and N-specific V3 peptides EIA. Using the same peptide assay, more than 120 wild caught young chimpanzees captured in Cameroon, Gabon and Congo were tested. Results: 97% of the human samples reacted with the M group peptide, 2% with the O group peptide and three samples (0.1%) with group N peptide. Fragments of coding sequence for integrase, gp41, V3 env regions and vif were amplified for these three new group N strains (designed YBF106, YBF115 and YBF116). In addition, the full-length sequence of YBF106 was obtained. Phylogenetic analysis showed a monophyletic clustering of all five group N strains in all regions analyzed. Among the chimpanzees studied, a high rate of positive sera was found in regard to the age of tested animals. Three P. t. troglodytes, from Cameroon and Gabon were positive, reacting specifically with the N peptide. Two of these SIVcpz strains, Cam3 and Cam5, were isolated and fully sequenced. The HIV-1 group N and SIVcpz strains form a monophyletic cluster in env region while in vif and the gag region the SIVcpz and human strains are more divergent. Conclusions: These new sequences confirm a primate-human cross-species transmission and the circulation of related SIV/HIV group N strains in humans and chimpanzees. Lack of infection of juvenile chimps points to the need for epidemiological studies of adult primate populations which may allow a better understanding of the missing links in the origins of HIV groups M and O.