Viral 'Fossils' in Birds Reveal that Past Infections Were More Common in Mammals

It turns out that the genomic "fossils" of past viral infections may be far more common in mammals than in birds. In fact, scientists found that they're 13 times less common in birds than in mammals.

The researchers sequenced, assembled and compared the full genomes of 48 bird species. After four years of collaboration with other scientists, the researchers revealed new insights into how birds evolved over time; and this, of course, included viral infection.

"We found that only five viral families have left a footprint in the bird genome (genetic material) during evolution," said Edward Holmes, one of the researchers, in a news release. "Our study therefore suggests that birds are either less susceptible to viral invasions or purge them more effectively than mammals. The results shed light on virus-host interactions across 100 million years of bird evolution."

Viral fossils are essentially copies of viruses that have been incorporated into the avian genome and then passed on through generations. This, in turn, can tell researchers more about past infections.

"Using comparative genomics we have shown that birds carry far fewer of these viral or genomic fossils than mammals," said Holmes. "Only five viral families have visited during bird evolution, with retroviruses and heapadnaviruses (like hepatitis B virus) the most common. Clearly, our next question is whether the small genomes carried by birds somehow favor a reduction in the number of these viral fossils?"

The findings reveal a bit more about bird evolution and, more specifically, virus-host interactions. This could pave the way for further discoveries.

The findings are published in the journal Science.

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