Retroviruses hundreds of millions of years older than we once thought

10 Jan 2017

3D rendering of a virus. Image: Rost9/Shutterstock

The origin story of retroviruses has been thrown wide open, following new research that has found them to be half a billion years old, hundreds of millions of years older than we previously thought.

Retroviruses – a family of viruses that includes potentially lethal ones like HIV and other immunodeficiencies – have previously been considered newcomers on the scene.

However, researchers from Oxford University have used genetic sequencing to discover that the previous age estimate of 100m years old is off by a considerable distance.

According to the team’s research, published in Nature Communications, retroviruses are actually closer to more than half a billion years old, increasing its age by hundreds of millions of years.

If this is correct, then its origins are not within land creatures – they can be traced back to ancient marine life, and carried over during their transition to land-based creatures.

The retrovirus family differs from normal cells, consisting of RNA that can be converted into DNA, allowing themselves to be inserted into the host genome.

This property means that they can occasionally be inherited as endogenous retroviruses (retroviruses with an internal origin), forming a virtual genomic fossil record that can be used to look back into their evolutionary history.

Closer to unravelling mysterious origins

Crucial to the team’s research was the ability to overcome a retrovirus’s ability to rapidly evolve, which can make tracing its distant past difficult.

However, a new research model used in combination with the genomic fossil records allowed the scientists to account for an apparent slowdown in the rate of evolution the further back they went.

“These findings show that this medically important group of viruses is at least up to half a billion years in age – far older than previously thought,” said the study’s lead author, Dr Aris Katzourakis.

“They date back to the origins of vertebrates, and this gives us the context in which we should consider their present-day activity and interactions with their hosts.

“As we build a clearer picture of the origins of the diverse groups of viruses that infect us today, we should come closer to unravelling the mystery of their ultimate origins.”

Colm Gorey was a senior journalist with Silicon Republic