Abstract
The human AIDS viruses human immunodeficiency virus type 1 (HIV-1) and
type 2 (HIV-2) represent cross-species (zoonotic) infections.
Although the primate reservoir of HIV-2 has been clearly identified as the
sooty mangabey (Cercocebus atys),,
the origin of HIV-1 remains uncertain. Viruses related to HIV-1 have been
isolated from the common chimpanzee (Pan troglodytes),
but only three such SIVcpz infections have been documented,,, one of which involved a virus so divergent 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.
