New research has suggested the family of viruses that includes HIV survived the evolutionary transition from sea to land, which would make them several hundred million years older than previously thought.
The study by scientists at Oxford University found that retroviruses – including the HIV virus responsible for the AIDS pandemic – are almost half a billion years old. But until recently, it was thought that retroviruses were only 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 Paleozoic era,” says study author Dr Aris Katzourakis, from Oxford University’s Department of Zoology.
“Furthermore, they would have been present in our vertebrate ancestors prior to the colonisation of land and have accompanied their hosts throughout this transition from sea to land, all the way up until the present day.”
In order to date retroviruses, the researchers overcame one of the key limitations in studying the deep evolutionary history of viruses: their rapid evolution.
To combat this, a new model was used that allowed for the reconstruction of the viruses’ distant past in addition to their recent history.
Using this model, the researchers were able to speculate on the present-day activity of retroviruses as well as the adaptations that have been developed to combat them.
“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,” says Katzourakis.
The Oxford scientists’ next step will be to consider the adaptations that vertebrates have developed to combat viruses and the corresponding viral countermeasures, as well as discerning viruses like HIV’s exact origin.
“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,” says Katzourakis.
“And 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.”
The paper ‘Marine origin of retroviruses in the early Palaeozoic Era’ is published in Nature Communications.