Quick study: HIV's viral ancestor found in rabbits
THE QUESTION: Since the emergence of AIDS and HIV, the human immunodeficiency virus, in the early 1980s, scientists have been intrigued by the origins of this virus known to belong to an unusual group of retroviruses called lentiviruses. HIV's high rate of mutation has allowed researchers to reconstruct a detailed picture of its evolution over recent decades. However, the more distant origins of HIV and other lentiviruses are controversial. This is partly because, unlike other retroviruses, ancient lentiviruses have not been identified in any animal's genome. Might there be such a lentiviral "fossil" out there somewhere that could provide information about millions of years of viral evolution?
THE STUDY: Analysis of the remains of a retrovirus that has hunkered down in the DNA of an animal can—through genetic and mathematical techniques—provide clues to its age and evolutionary history. To search for any animal that might harbor an ancient lentivirus in its DNA, the researchers screened genome data from 46 different species. They uncovered the genetic remains of a lentivirus in one: the European rabbit. Previously, lentiviruses had only been known to infect cats, primates and hoofed mammals.
The researchers estimated that this virus—called RELIK for Rabbit Endogenous Lentivirus type K—had infected rabbits approximately 5.7 to 7 million years ago. This figure triples previous estimates of how long lentiviruses had been around. Much like digging up a fossil of an animal no one suspected existed, finding this virus demonstrated the previously unknown ability for this type of virus to be passed through generations rather than by direct infection.
WHY IT MATTERS: RELIK may help researchers better understand the relationship between lentiviruses and their hosts' immune systems, which can evolve together to develop strategies to thwart each other. It provides an ancient footprint for tracing the origins of other lentiviruses, such as HIV. The researchers hope to bring RELIK back to life by recreating the virus in the laboratory, as has been done with other extinct retroviruses.
STANFORD CONNECTION: The study's senior author is Robert Gifford, PhD, a postdoctoral scholar in the department of medicine (infectious diseases).
FIND THIS STUDY published in the March 23 online version of Proceedings of the National Academy of Sciences: http://www.pnas.org/cgi/reprint/.