Résumé
The human AIDS viruses human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) represent cross-species (zoonotic) infections
1
,
2
,
3
,
4
. Although the primate reservoir of HIV-2 has been clearly identified as the sooty mangabey (
Cercocebus atys
)
2
,
4
,
5
,
6
,
7
, the origin of HIV-1 remains uncertain. Viruses related to HIV-1 have been isolated from the common chimpanzee (
Pan troglodytes
)
8
,
9
, but only three such SIVcpz infections have been documented
1
,
10
,
11
, one of which involved a virus so divergent
11
that it might represent a different primate lentiviral lineage. In a search for the HIV-1 reservoir, we have now sequenced the genome of a new SIVcpz strain (SIVcpzUS) and have determined, by mitochondrial DNA analysis, the subspecies identity of all known SIVcpz-infected chimpanzees. We find that two chimpanzee subspecies in Africa, the central
P. t. troglodytes
and the eastern
P. t. schweinfurthii
, harbour SIVcpz and that their respective viruses form two highly divergent (but subspecies-specific) phylogenetic lineages. All HIV-1 strains known to infect man, including HIV-1 groups M, N and O, are closely related to just one of these SIVcpz lineages, that found in
P. t. troglodytes
. Moreover, we find that HIV-1 group N is a mosaic of SIVcpzUS- and HIV-1-related sequences, indicating an ancestral recombination event in a chimpanzee host. These results, together with the observation that the natural range of
P. t. troglodytes
coincides uniquely with areas of HIV-1 group M, N and O endemicity, indicate that
P. t. troglodytes
is the primary reservoir for HIV-1 and has been the source of at least three independent introductions of SIVcpz into the human population.