Boston College researchers have uncovered the worldwide spread of an ancient group of retroviruses that affected ancestors of roughly 28 of 50 modern mammals nearly 15 to 30 million years back.

Retroviruses are widespread and consists human immunodeficiency viruses (HIV-1 and -2) and human T-cell leukemia viruses. The findings of the scientists on a particular group of these viruses known as ERV-Fc have shown that they affected a large number of hosts, like species as diverse as primates, carnivores, and rodents. The results will appear in journal eLife.

ERV-Fc distribution among such ancient mammals has suggested that the viruses spread across every continent leaving aside Antarctica and Australia. It has also indicated that they had jumped from one species to another over 20 times.

As per the study, the ERV-Fc originated as far back as the starting of the Oligocene epoch, a time of dramatic global change that is popular partly by climatic cooling that resulted in the Ice Ages.

Around these times, emergence of vast expanses of grasslands took place along with big mammals as they predominated fauna across the world.

Co-author Welkin Johnson, Professor of Biology at Boston College, said that viruses have been there for billions of years. They are present wherever there is life. Thus, they have a lot of impact on the ecology and evolution of all organisms, ranging from bacteria to humans.

Johnson added, “Unfortunately, viruses don’t leave fossils behind, meaning we know slight about their origination and evolution. Over millions of years, however, viral genetic sequences accumulate in DNA genomes of living organisms, and can serve as molecular 'fossils' for exploring natural history of viruses, their hosts”. With the help of such ‘fossil’ leftovers, the team wanted to discover the natural history of ERV-Fc.