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History of Ancient 30 Million Year Old Retrovirus Revealed

The history of an ancient retrovirus that infected organisms 15 to 30 million years ago has been revealed in a study published in eLife. The virus was found to have jumped from species to species, spanning from primates to rodents.

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A global viral epidemic having once affected the ancestors of mammals — 15 to 30 million years ago — has been revealed in the findings of a team of researchers from Boston College, US.

The pathogen is from an ancient family of retroviruses, a particular group known as ERV-Fc. The latter are known to be quite ubiquitous in our modern world, and they include the HIV and the human T-cell leukemia ones. ERV-Fc might have been in existence at the start of the Oligocene era, the time characterised by dramatic changes all over the world including events that led to the Ice Ages, and by the emergence of grasslands and the predominance of large mammals.

It is, otherwise, challenging to find out about the origin and evolution of viruses because they “do not leave fossils behind”, as pointed out by co-author Welkin Johnson. Fortunately, though, we can learn of how some viruses originate by studying the viral genetic sequences that have been embedded in the genome of living organisms. Part of the natural history of viruses (and their hosts) can thus be revealed by using these “molecular fossils”, says Johnson.

Based on the information encoded in the “molecular fossils” spotted in the genomes of many species of mammals, the researchers reconstructed protein sequences characterising the virus. The natural history and evolution of relatives of the ERV-Fc viruses were deciphered from there.

That was how the team found that the virus in question was able to infect a variety of hosts, from carnivores to rodents to primates. It appears that the virus would go from one species to another — this might have happened over 20 times. Also, the viruses would exchange genes with other viruses of their own type and others, implying that genetic recombination might have contributed to their evolution.

Furthermore, the findings pertaining to how ERV-Fc was distributed allude to the possibility of a viral propagation from continent to continent (excluding Antarctica and Australia) — a global epidemic.

Ultimately, this type of data will provide for a better understanding of the emergence of new viruses, and could help forecast the long-term effects of new viral infections; for instance, the consequences relating to HIV in 30 million years from now might be predicted.

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