Thus, in addition to representing a potential source for human infection, SIVcpz also comprises a serious threat to chimpanzee populations living in the wild ( 54).Ĭhimpanzees are highly endangered, thus requiring noninvasive approaches to study SIVcpz infection in wild populations ( 59, 60). Importantly, natural history studies have shown that SIVcpz is quite pathogenic and has a substantial negative impact on the health, reproduction, and life span of its natural host ( 17, 29, 54, 74).
Chimpanzees also differ from most other primate species by having acquired their infection relatively more recently, as a consequence of cross-species transmission and recombination of viruses infecting monkeys on which they prey ( 3). It is now well established that chimpanzees are the original source of viruses currently found in chimpanzees, gorillas, and humans and that ape viruses have been transmitted to humans on at least four occasions, generating human immunodeficiency virus type 1 (HIV-1) groups M, N, O, and P ( 24, 64, 65). Of over 40 African primate species naturally infected with simian immunodeficiency viruses (SIVs), chimpanzees ( Pan troglodytes) are unique because they harbor the virus (SIVcpz) that spawned the human AIDS pandemic ( 20, 30, 78). Instead, greater adaptive hurdles may have prevented the successful colonization of humans by P. Thus, the absence of SIVcpz Pts zoonoses cannot be explained by an insufficient primate reservoir. All newly identified SIVcpz Pts strains clustered in strict accordance to their subspecies origin however, they exhibited considerable genetic diversity, especially in protein domains known to be under strong host selection pressure. In contrast, none of the 543 bonobo samples from six sites was antibody positive. The overall prevalence of SIVcpz Pts infection was 13.4% (95% confidence interval, 10.7% to 16.5%).
In this region, SIVcpz Pts was common and widespread, with seven field sites exhibiting infection rates of 30% or greater. The antibody-positive samples represented 76 individuals from 19 field sites, all sampled north of the Congo River in an area spanning 250,000 km 2. Of 2,565 samples from eastern chimpanzees, 323 were antibody positive and 92 contained viral RNA. Fecal samples ( n = 3,108) were collected at 50 field sites, tested for species and subspecies origin, and screened for SIVcpz antibodies and nucleic acids. We also screened bonobos ( Pan paniscus) in the DRC, a species not previously tested for SIV in the wild. To examine whether this is due to a paucity of natural infections, we used noninvasive methods to screen wild-living eastern chimpanzees in the Democratic Republic of the Congo (DRC), Uganda, and Rwanda. Chimpanzees in east Africa ( Pan troglodytes schweinfurthii) are also infected with SIVcpz however, their viruses (SIVcpz Pts) have never been found in humans. Chimpanzees in west central Africa ( Pan troglodytes troglodytes) are endemically infected with simian immunodeficiency viruses (SIVcpz Ptt) that have crossed the species barrier to humans and gorillas on at least five occasions, generating pandemic and nonpandemic forms of human immunodeficiency virus type 1 (HIV-1) as well as gorilla SIV (SIVgor).
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