It is common knowledge that the HIV/AIDS pandemic in humans was ignited by the transmission of simian immunodeficiency viruses (SIV) in chimpanzees and monkeys. Now, in a surprising discovery, scientists have found that the ancestors of SIVs originated just a few centuries ago.
The new study from The University of Arizona in Tucson revealed that these ages are substantially younger than previous estimates.
SIV has crossed over from chimpanzees and sooty mangabeys to humans at least eleven times, giving rise to several HIV lineages.
While HIV is a virulent pathogen in humans, SIV rarely causes disease in these species or the dozens of other African primate species it naturally infects.
And because these non-human primates typically remain unaffected after virus exposure, scientists had hypothesised that there had been millions of years of coevolution between SIVs and their primate hosts.
But, in the new study, researchers, Joel Wertheim and Dr. Michael Worobey, estimated a rate of virus evolution using viral genetic sequences that had been isolated from infected humans, chimpanzees, and sooty mangabeys between 1975 and 2005.
And their analysis revealed that the viruses currently circulating in sooty mangabeys and in chimpanzees evolved from ancestors dating to 1809 and 1492, respectively.
To their surprise, they found that the independently estimated 'molecular clock' of the monkey viruses was virtually identical to the famously swift rate at which mutations accumulate in HIV genomes.
The authors pointed out that unaccounted-for biases could be masking a deeper age of SIV.
They suggested that presence of these biases indicates a need for investigation because they might also affect the ability to properly estimate the age of HIV and other viruses.
The study is published in the open-access journal PLoS Computational Biology.