50,000-year-old Neanderthal bones harbor oldest-known human viruses

Neanderthals who lived 50,000 years ago were infected with three viruses that still affect modern humans today, researchers have discovered. 

These traces of ancient viruses are the oldest remnants of human viruses ever discovered, New Scientist reported. They are around 20,000 years older than the previous record-holder for the most ancient human virus ever found: a common-cold virus uncovered inside a pair of 31,000-year-old baby teeth in Siberia.

Scientists found the ancient viruses after sifting through DNA sequences drawn from the skeletons of two male Neanderthals originally found in the Chagyrskaya cave, located in the Altai mountains in Russia. Several sequences appeared to be viral in origin, so the team compared them to modern viruses known to cause lifelong infections. They ruled out the possibility that the viruses came from modern humans who handled the skeletons or by predators that fed on them by looking at specific signatures in the viral DNA that differed between the ancient and modern samples. 

In this way, they showed that our closest, now-extinct relatives could be infected with three common, modern human viruses: a type of adenovirus, a herpesvirus and a papillomavirus. 

Related: 'More Neanderthal than human': How your health may depend on DNA from our long-lost ancestors 

In modern humans, adenoviruses can cause a range of symptoms, including cold- and flu-like symptoms, sore throat and pink eye. Infection with sexually transmitted papillomaviruses can lead to genital warts and certain types of cancer, while different herpesviruses can trigger cold sores, chickenpox or "mono." The herpesvirus found in the Neanderthals looked most like the one that causes cold sores.

The researchers behind the new study say the findings provide physical evidence to support the theory that viruses may have played a role in the demise of the Neanderthals, who went extinct around 40,000 years ago. The findings, published Tuesday (May 21) to the preprint server bioRxiv, have not yet been peer-reviewed.