14 DAY TRIAL // Virus fragments from the family of the modern Hepatitis B virus, locked inside the genomes of songbirds such as the modern-day zebra finch, were discovered by biologists from The University of Texas at Arlington.
This is actually the first time that endogenous hepadnaviruses have been found in any organism whatsoever.
A virus that deposits itself (or even fragments of itself) into the chromosome of an organism, allowing it to be passed from generation-to-generation in this way, is an endogenous virus, and most of these “fossilized” virus sequences came from retroviruses.
Cédric Feschotte and Clément Gilbert, co-authors of the study, said that these virus sequences “have been sitting there for at least 19 million years, far longer than anyone previously thought this family of viruses had been in existence.”
The two dated the hepadnavirus fragments by identifying them in the same place, on the genome of five species of passerine birds and them finding their common ancestor, which lived over 19 million years ago.
Eddie Holmes, who is an expert in viral evolution and a distinguished professor of biology at Penn State University's Eberly College of Science, said that this work “provides a glimpse into an ancient viral world that we never knew existed.”
"The results they obtained were remarkable,” he added; whereas we previously thought of hepadnavirus evolution on time-scales of only a few thousand years, this paper shows that the true time-scale is in fact many million years.
“Therefore, hepadnaviruses, and likely many other viruses as well, are far older than we previously thought," said Holmes.
Another very strange thing is that the old versions of the hepadnaviruses resemble a lot the viruses we have today.
Feschotte explains this slow evolution by saying that these viruses must have adapted to their host much better than studies of the Hepatitis B viruses previously suggested.
Harmit Singh Malik, an associate member of the Fred Hutchinson Cancer Research Center in Seattle and one of the leaders in the new field of 'paleovirology' said that “genomic fossils like the remarkable hepadnaviral fossils found by Gilbert and Feschotte have the prospect of completely revising our preconceived notions about the age and evolution of such viruses.
“They provide an unexpectedly clear lens on an ancient time when these viruses were prevalent and abundant.”
The research can also help predict and prevent human viral pandemics that are originated in bird species.
“Given that they were infected in the past, it is legitimate to think that some of these birds may still carry such viruses today,” Gilbert said.
“We can therefore use this discovery as a guide to screen targeted groups of bird species for the presence of new circulating Hepatitis B-like viruses.”
Feschotte is an associate professor and member of the UT Arlington Genome Biology Group and Gilbert is a post-doctoral research associate in the group.
The article will be published next week in the online, open access journal PLoS Biology.