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When People First Kissed, Herpes Spread

FILE: Representative illustration of two persons kissing.

The modern strain of the virus that causes cold sores has been traced back to around 5,000 years ago, with researchers suggesting its spread could have been propelled by the emergence of kissing.

All primate species have a form of herpes and humans likely had a strain when they first left Africa.

But the research indicated that those earlier strains were replaced by the modern form around 5,000 years ago.

So what brought about that change? The researchers suggested two theories.

Around 5,000 years ago was a time of great migration from Eurasia into Europe, and that spread could have affected the virus.

The other theory? That was around the time when people starting romantically kissing each other.

Despite its ubiquity, relatively little has been known about the history of this virus, or how it spread throughout the world.

So an international team of researchers screened the DNA of teeth in hundreds of people from ancient archaeological finds.

"Using these reconstructed genomes, we were able to determine that the variations of modern strains all trace back to some time in the late Neolithic, early Bronze Age," said the study's co-senior author Christiana Scheib of Cambridge University.

"There is some textual evidence starting to show in the Bronze Age of kissing between romantic partners," Scheib said.

The researchers said the earliest known record of kissing was a manuscript from South Asia during the Bronze Age, suggesting the custom may have also migrated from Eurasia into Europe.

Kissing "is not a universal human trait," Scheib pointed out, emphasising that it is difficult to trace exactly when it began -- or if it is definitively linked to the spread of HSV-1.

Around 2,000 years ago, the Roman Emperor Tiberius was believed to have attempted to ban kissing at official functions to prevent the spread of herpes.

The virus is normally passed by a parent to their child, but kissing would have given it a whole new way to jump between hosts, she said.

Co-senior study author Charlotte Houldcroft, also from Cambridge, said "Facial herpes hides in its host for life and only transmits through oral contact, so mutations occur slowly over centuries and millennia," she said.

This research may help science gain better knowledge about the spread of other viruses.

"Only genetic samples that are hundreds or even thousands of years old will allow us to understand how DNA viruses such as herpes and monkeypox, as well as our own immune systems, are adapting in response to each other."