Many of the viruses infecting humans today have evolved from ancient animals and can even be traced back to the first vertebrates ever to exist, according to new research.

The study by researchers at The University of Sydney along with the China Center for Disease Control and Prevention and the Shanghai Public Health Clinical Centre, has been published in the journal ‘Nature’ and offers new insight on the modern-day understanding of viruses.

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The team says it made its discovery by looking for RNA – rather than DNA – viruses in 186 animal species not previously covered in viral infection studies. In doing so, they found 214 novel RNA viruses in apparently healthy reptiles, amphibians, lungfish, ray-finned fish, cartilaginous fish and jawless fish.

“This study reveals some groups of virus have been in existence for the entire evolutionary history of the vertebrates – it transforms our understanding of virus evolution,” said Professor Eddie Holmes, of the Marie Bashir Institute for Infectious Diseases & Biosecurity at the University of Sydney.

“For the first time we can definitely show that RNA viruses are many millions of years old, and have been in existence since the first vertebrates existed.”

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Fish, in particular, carry an “amazing” diversity of viruses, says Holmes, as virtually every type of virus family detected in mammals is now found in fish. “We even found relatives of both Ebola and influenza viruses in fish,” the professor added.

The array of viruses fish carry does not, however, pose a threat to human health, says Holmes, and are a natural part of virus biodiversity.

“This study emphasises just how big the universe of viruses – the virosphere – really is. Viruses are everywhere,” said the professor, who added that more research is needed to identify the “many millions more viruses still to be discovered”.

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