researchers from boston college, us, have revealed the global spread of an ancient group of retroviruses that
1 about 28 of 50 modern mammals' ancestors some 15 to 30 million years ago. retroviruses are abundant in nature and include human immunodeficiency viruses (hiv-1 and -2) and human t-cell leukemia viruses. the scientists' findings on a specific group of these viruses called erv-fc, to be published in the journal elife, show that they affected a wide range of hosts, including species as diverse as carnivores,
2, and
3.
the distribution of erv-fc among these ancient mammals suggests the viruses spread to every continent except antarctica and australia, and that they jumped from one species to another more than 20 times.
the study also places the origins of erv-fc at least as far back as the beginning of the oligocene
4, a period of dramatic global change marked partly by climatic cooling that led to the ice ages. vast expanses of
5 emerged around this time, along with large mammals as the world's predominate
6.
"viruses have been with us for billions of years, and exist everywhere that life is found. they therefore have a significant impact on the ecology and evolution of all organisms, from bacteria to humans," says co-author welkin johnson, professor of biology at boston college where his team carried out the research.
"unfortunately, viruses do not leave fossils behind, meaning we know very little about how they originate and evolve. over the course of millions of years, however, viral
7 sequences accumulate in the
8 genomes of living organisms, including humans, and can serve as
9 'fossils' for exploring the natural history of viruses and their hosts."
using such "fossil" remnants, the team sought to uncover the natural history of erv-fc. they were especially curious to know where and when these pathogens were found in the ancient world, which species they infected, and how they adapted to their mammalian hosts.
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