TUCSON, Sept. 16 (UPI) — An ancestor of the AIDS virus is thousands of years older than previously thought, suggesting HIV will be around for some time yet, U.S. scientists say.
Simian immunodeficiency virus or SIV, which infects monkeys, took thousands of years, not hundreds as previously believed, to evolve into a mostly non-lethal state, suggesting HIV will remain deadly to humans for a long time, University of Arizona researchers say.
SIV, unlike HIV, does not cause AIDS in most of its primate hosts. If it took thousands of years for SIV to become non-lethal, it would likely take a very long time for HIV to follow the same path, scientists say.
“HIV is the odd man out because, by and large, all the other species of immunodeficiency viruses impose a much lower mortality on their host species,” Michael Worobey, a professor in the Arizona’s department of ecology and evolutionary biology, said.
“So, if SIV entered the picture relatively recently as was previously thought, we would think it achieved a much lower virulence over a short timescale,” Worobey said. “But our findings suggest the opposite. If HIV is going to evolve to lower virulence, it is unlikely to happen anytime soon.”
The study raises questions about HIV, which scientists believe evolved from SIV.
If humans have been exposed to SIV-infected monkeys for thousands of years, not just hundreds, why did the HIV epidemic only begin in the 20th century?
“Something happened in the 20th century to change this relatively benign monkey virus into something that was much more potent and could start the epidemic,” virologist Preston Marx of Tulane University, co-author of the study, said. “We don’t know what that flash point was, but there had to be one.”
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