Human immunodeficiency virus type 1 (HIV-1), the cause of human acquired immunodeficiency syndrome (AIDS), is a zoonotic infection of staggering proportions and social impact. Yet uncertainty persists regarding its natural reservoir. The virus most closely related to HIV-1 is a simian immunodeficiency virus (SIV) thus far identified only in captive members of the chimpanzee subspecies Pan troglodytes troglodytes. Here we report the detection of SIVcpz antibodies and nucleic acids in fecal samples from wild-living P. t. troglodytes apes in southern Cameroon, where prevalence rates in some communities reached 29 to 35%. By sequence analysis of endemic SIVcpz strains, we could trace the origins of pandemic (group M) and nonpandemic (group N) HIV-1 to distinct, geographically isolated chimpanzee communities. These findings establish P. t. troglodytes as a natural reservoir of HIV-1.

No abstract

It is now well established that the clade of simian immunodeficiency viruses (SIVs) infecting west central African chimpanzees (Pan troglodytes troglodytes) and western gorillas (Gorilla gorilla gorilla) comprises the progenitors of human immunodeficiency virus type 1 (HIV-1). In this study, we have greatly expanded our previous molecular epidemiological survey of SIVcpz in wild chimpanzees in Cameroon. The new results confirm a wide but uneven distribution of SIVcpzPtt in P. t. troglodytes throughout southern Cameroon and indicate the absence of SIVcpz infection in Pan troglodytes vellerosus. Analyzing 725 fecal samples from 15 field sites, we obtained partial nucleotide sequences from 16 new SIVcpzPtt strains and determined full-length sequences for two of these. Phylogenetic analyses of these new viruses confirmed the previously reported phylogeographic clustering of SIVcpzPtt lineages, with viruses related to the ancestors of HIV-1 groups M and N circulating exclusively in southeastern and south central P. t. troglodytes communities, respectively. Importantly, the SIVcpzPtt strains from the southeastern corner of Cameroon represent a relatively isolated clade indicating a defined geographic origin of the chimpanzee precursor of HIV-1 group M. Since contacts between humans and apes continue, the possibility of ongoing transmissions of SIV from chimpanzees (or gorillas) to humans has to be considered. In this context, our finding of distinct SIVcpzPtt envelope V3 sequence clades suggests that these peptides may be useful for the serological differentiation of SIVcpzPtt and HIV-1 infections, and thus the diagnosis of new cross-species transmissions if they occurred.

Chimpanzees (Pan troglodytes troglodytes) from west central Africa are recognized as the reservoir of simian immunodeficiency viruses (SIVcpzPtt) that have crossed at least twice to humans: this resulted in the AIDS pandemic (from human immunodeficiency virus HIV-1 group M) in one instance and infection of just a few individuals in Cameroon (by HIV-1 group N) in another. A third HIV-1 lineage (group O) from west central Africa also falls within the SIVcpzPtt radiation, but the primate reservoir of this virus has not been identified. Here we report the discovery of HIV-1 group O-like viruses in wild gorillas.

To evaluate the risk of cross-species transmissions of SIVs from non-human primates to humans at the primate/hunter interface, a total of 2586 samples, derived from primate bushmeat representing 11 different primate species, were collected at 6 distinct remote forest sites in southeastern Cameroon and in Yaoundé, the capital city. SIV prevalences were estimated with an updated SIV lineage specific gp41 peptide Elisa covering the major part of the SIV diversity. SIV positive samples were confirmed by PCR and sequence analysis of partial pol fragments. The updated SIV Elisa showed good performance with overall sensitivity and specificity of 96% and 97.5% respectively. The overall SIV seroprevalence was low, 2.93% (76/2586) and ranged between 0.0% and 5.7% at forest sites, and reached up to 10.3% in Yaoundé. SIV infection was documented in 8 of the 11 species with significantly different prevalence rates per species: 9/859 (1.0%) in Cercopithecus nictitans, 9/864 (1.0%) Cercopithecus cephus, 10/60 (16.7%) Miopithecus ogouensis, 14/78 (17.9%) Colobus guereza, 15/37 (40.5%) Cercopithecus neglectus, 10/27 (33.3%) Mandrillus sphinx, 6/12 (50%) Cercocebus torquatus, and 3/6 (50%) Chlorocebus tantalus. No SIV infection was identified in Cercopithecus pogonias (n=293), Lophocebus albigena (n=168) and Cercocebus agilis (n=182). The SIV prevalences seem to vary also within species according to the sampling site, but most importantly, the highest SIV prevalences are observed in the primate species which represent only 8.5% of the overall primate bushmeat. The phylogenetic tree of partial pol sequences illustrates the high genetic diversity of SIVs between and within different primate species. The tree showed also some interesting features within the SIVdeb lineage suggesting phylogeographic clusters. Overall, the risk for additional cross-species transmissions is not equal throughout southern Cameroon and depends on the hunted species and SIV prevalences in each species. However, humans are still exposed to a high diversity of SIVs as illustrated by the high inter and intra SIV lineage genetic diversity.