Ancient Viruses

Viruses as we know them possess the ability to rapidly adapt allowing them to overcome various obstacles to infection. Recently conducted research has discovered that there are ancient traces of many viruses in animal genomes. These DNA insertions are likely to have been present for far longer than previously thought, even longer than the viruses were thought to have existed. Particularly, a new study has produced evidence of a hepadnavirus inside the genome of a modern day bird. This virus group is especially interesting since it includes hepatitis B, a well know virus which infects humans, causing inflammation of the liver and killing about 600,000 people worldwide each year, as well as other mammals and ducks. It is estimated that this particular group of viruses has existed for approximately 19 million to 40 million years. This estimation is vastly different from the several thousand years scientists had previously estimated. So how were we so wrong?

The new findings have drastically changed and complicated our understanding of how viruses evolve. The new research seems to promise to help us have a more complete understanding of how viruses move among different host species. Already the new estimates have slowed the average rate of hepadnavirus mutation by 1,000 times. The researchers believe that in order for hepadnaviruses to be passed along for millions of years they would have needed to insert genetic material into the sperm or egg cell of their hosts on multiple occasions. Feschotte suggests that “it is likely having a bit of the virus’s code integrated in a bird’s genome might have conferred immune protection against similar viruses.” I found it particularly interesting that the viral fragments were all located in exactly the same genomic position leading the researchers to conclude that the hepadnaviruses were incorpereated into the genes of common ancestors millions of years ago passing their genetic code down to new species as they evolved.

This research will provide a far greater understanding of viral history and could possibly lead to advances in the way we treat modern illnesses. The researchers propose that the extreme difference in the previously found viral mutation rate and the proposed new rates was due to many of the viruses being studied have crossed over to a new species within the past thousands of years and therefore is in an adaptation phase. It is incredible that we will be able to further study, assess and reassemble once extinct viruses and gain knowledge that will impact our future.

http://www.scientificamerican.com/article.cfm?id=fossil-virus-bird-genome