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Thus, it is possible that at least some SIVs, such as those infecting four closely related species of African green monkeys ( species), have coevolved with their respective hosts for an extended period of time, perhaps even before these hosts diverged from their common ancestor (Jin et al. So far, SIV infections have only been found in African monkeys and apes, and so it seems likely that primate lentiviruses emerged in Africa sometime after the splits between lineages of African and Asian Old World monkeys, which are believed to have occurred around 6–10 million years ago (Fabre et al. However, because neither Asian nor New World primates have been sampled exhaustively, the conclusion that SIVs are restricted to African primates must remain tentative, especially because none of these primate species has been examined for endogenous forms of SIV (Ylinen et al. Thus, our understanding of the evolutionary history of primate lentiviruses is still incomplete.
Here, we describe the origins and evolution of these viruses, and the circumstances that led to the AIDS pandemic.
The first isolates of SIVcpz were all derived from animals housed in primate centers or sanctuaries, although infection was rare in these populations. 2005), this finding raised doubts about whether chimpanzees represented a true SIV reservoir. These technical innovations, combined with genotyping methods for species and subspecies confirmation as well as individual identification, permitted a comprehensive analysis of wild-living chimpanzee populations throughout central Africa.
Collective analyses of nearly 2,000 wild-caught or captive-born apes identified fewer than a dozen SIVcpz positive individuals (Sharp et al. Because other primate species, such as sooty mangabeys and African green monkeys, are much more commonly infected, both in captivity and in the wild (Fultz et al. To resolve this conundrum, our laboratory developed noninvasive diagnostic methods that detect SIVcpz specific antibodies and nucleic acids in chimpanzee fecal and urine samples with high sensitivity and specificity (Santiago et al. Chimpanzees are classified into two species, the common chimpanzee (). These studies have identified common chimpanzees as a natural SIVcpz reservoir, but also revealed important differences between the epidemiology of SIVcpz and that of other primate lentiviruses.
Antibody positive fecal specimens were then subjected to RNA extraction and reverse transcriptase polymerase chain reaction (RT-PCR) amplification to molecularly characterize the infecting virus strain. In addition, SIVcpz prevalence rates among central and eastern chimpanzees varied widely, ranging from 30% to 50% in some communities to rare or absent infection in others. Nonetheless, the puzzle of why SIVcpz was so scarce among captive chimpanzees was finally resolved: As it turned out, most of these apes were imported from West Africa and thus were members of the ) gorillas have been sampled are shown (each site is identified by a two-letter code; because of space limitations, only a subset is depicted). The current range of the central chimpanzee overlaps those of red-capped mangabeys and the various species, and so it is likely that the cross-species transmission events that led to the emergence of SIVcpz occurred in that area, and that SIVcpz later spread to eastern chimpanzees, although it is unclear whether this occurred during or subsequent to their divergence from the central subspecies.
At select field sites, mitochondrial and microsatellite analyses of host DNA were also used to confirm sample integrity and to determine the number of tested individuals. In contrast, other SIVs, such as those of sooty mangabeys and African green monkeys, are much more widely and evenly distributed and infect their hosts at generally higher prevalence rates (Phillips-Conroy et al. Sites where SIV infections were detected are highlighted in yellow. Importantly, all of more than 30 sequenced SIVcpz strains show an identical mosaic genome structure.