Lentiviruses cause chronic persistent infections in various mammalian species, including bovines, horses, sheep, felines, and primates.The great majority of lentiviruses are exogenous, meaning that they are transmitted horizontally between individuals. These “viral fossils” are of particular interest because they provide direct evidence of the timescale of lentivirus evolution.[When Natalie Wood began dating Warren Beatty] I wanted to kill that son of a bitch...
However, the sporadic prevalence of SIVcpz, along with its more recent monkey origin, suggested that its natural history might differ from that of other primate lentiviruses.
To address this, a prospective study was initiated in Gombe National Park, Tanzania, the only field site where SIVcpz infected chimpanzees are habituated and so can be observed in their natural habitat.
Most of these transfers resulted in viruses that spread in humans to only a limited extent.
However, one transmission event, involving SIVcpz from chimpanzees in southeastern Cameroon, gave rise to HIV-1 group M—the principal cause of the AIDS pandemic.
Four subspecies were defined on the basis of mitochondrial DNA sequences (Gagneux et al. To determine the distribution of SIVcpz among these populations, fecal (and in some cases urine) samples were collected at different field sites and tested for the presence of virus specific antibodies. SIVcpz was detected at multiple sites throughout the ranges of both central and eastern chimpanzees in an area ranging from Cameroon to Tanzania, but there was no evidence of infection in western and Nigeria-Cameroonian chimpanzees, nor in bonobos, despite testing of multiple communities. Indeed, phylogenetic analyses of full-length proviral sequences revealed that SIVcpz represents a complex mosaic, generated by recombination of two lineages of SIVs that infect monkeys (Bailes et al. In the 5′ half of the genome, as well as the ) monkeys (Bailes et al. Chimpanzees are known to hunt and kill other mammals, including monkeys (Goodall 1986), suggesting that they acquired SIV in the context of predation.
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.The prevalence of naturally occurring SIV infections varies widely, ranging from 1% in some species to over 50% in others (Aghokeng et al.2010), and it is tempting to speculate that less ubiquitous SIVs were acquired more recently and/or may be more pathogenic.To date, serological evidence of SIV infection has been reported for over 40 primate species, and molecular data have been obtained for most of these (also see Klatt et al. The latter studies have shown that the great majority of primate species harbor a single “type” or “strain” of SIV.That is, viral sequences from members of the same species form a monophyletic clade in evolutionary trees.A first clue came in 1986 when a morphologically similar but antigenically distinct virus was found to cause AIDS in patients in western Africa (Clavel et al. Curiously, this new virus, termed human immunodeficiency virus type 2 (HIV-2), was only distantly related to HIV-1, but was closely related to a simian virus that caused immunodeficiency in captive macaques (Chakrabarti et al. Known examples of cross-species transmissions, as well as the resulting viruses, are highlighted in red. The evolutionary relationships among Pol sequences (∼ 770 amino acids) derived from various mammalian lentiviruses; host species are indicated at the right.