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Ancient Retroviruses Date Back to Palaeozoic Era, 500 Million Years Ago

RETROVIRUSES, the family of viruses that includes HIV, are nearly half a billion years old, according to research from the University of Oxford, Oxford, UK.

The findings show that the viruses are at least 450 million years old which also makes them hundreds of millions of years older than previously thought. Their origins are believed to be located in the Palaeozoic era where they accompanied their animal hosts in their transition from the sea to land.

“Retroviruses are broadly distributed among vertebrates and can also transmit between hosts, leading to novels diseases such as HIV, and they have been shown to be capable of leaping between distantly related hosts such as birds and mammals,” explained study author, Dr Aris Katzourakis, from the University of Oxford’s Department of Zoology. “Until now, it was thought retroviruses were relative newcomers, possibly as recent as 100 million years in age. Our new research shows that retroviruses are at least 450 million years old, if not older, and that they must have originated together with, if not before, their vertebrate hosts in the early Palaeozoic era.”

Retroviruses are a family of viruses that can cause cancers and immunodeficiencies in a range of animals. The ‘retro’ part of their name comes from them being made of RNA, which they convert into DNA and insert into the genome of their host. This is the opposite direction to the normal flow of information in a cell which means they can sometimes be inherited as endogenous retroviruses. This means they form a virtual genomic fossil record which can be used to look back into their evolutionary history.

In the study, the researchers sequenced the genomes to track the evolution of endogenous retroviruses stretching back millions of years. Dr Katzourakis also added: “Our inferred date of the origins of retroviruses coincides with the origins of adaptive immunity, and thus it is likely that retroviruses have played an important role in the emergence of this key tool in vertebrate antiviral defence. As we understand the nature of the interaction between viruses and host immunity, we will be better placed to intervene in this delicately balanced arms race in order to develop novel treatments and interventions.”

Jack Redden, Reporter

Keywords: Adaptive Immunity, DNA, HIV, Retroviruses, RNA, Viruses