The herpes variants that cause modern cold sores became widespread in the wake of bronze age migrations, and may have received a boost from the practice of kissing that came with it, researchers say.
Scientists in Cambridge analysed the first ancient DNA specimens of herpes simplex virus and found that one variant overtook all others about 4,500 years ago, setting the course for its dominance today.
“The variants around in Europe today all share an ancestor in the bronze age,” said Dr Charlotte Houldcroft, a virologist on the study. “There were variants around before that, but those have been replaced, probably because of human behaviour.”
The herpes simplex virus, or HSV-1, infects nearly 4 billion people globally. It is thought to have emerged millions of years ago, before humans split from their primate relatives. But the lack of ancient herpes DNA has left scientists unclear as to how it has evolved since humans spread out of Africa.
Writing in Science Advances, the team describe how they screened ancient DNA recovered from about 3,000 archaeological sites and found only four individuals – from the UK, the Netherlands and Russia – who had herpes infections. Together, they span a 1,000-year period.
The oldest individual was an iron age man excavated from a burial site in the Ural mountains, dating to about 1,500 years old. Two others were buried in the Cambridge area: a woman in her 30s or 40s at an Anglo-Saxon cemetery at Edix Hill, and a man in his late teens or early 20s at St John’s hospital. A third skeleton, that of a man in his mid 20s to 30s, whose bent teeth betrayed a penchant for clay pipe smoking, came from a burial ground on the bank of the Rhine, a probable victim of a French attack on his village in 1672.
Analysis of the ancient DNA showed that the herpes virus then was remarkably similar to the virus seen today and could be traced back to the bronze age. The timing coincides with vast migrations into Europe from the grasslands of Eurasia and a population boom that could have sent transmission rates soaring.
But another factor may have come into play, the scientists suggest. The earliest known written record of kissing is a bronze age manuscript from south Asia. Far from being a cultural norm, kissing may have arrived with the westward migrations, providing a new route for the virus to spread. Until then, the argument goes, herpes was largely passed on from mother to child, limiting its transmission.
“If you suddenly have a group of people who are kissing, which was not a universal human behaviour, that is an extra way to spread the virus,” said Houldcroft.
But she said there was a need for more evidence. “Kissing is one of those behaviours that doesn’t fossilise well. The risks of kissing were certainly apparent to the Romans. Centuries later, Emperor Tiberius tried to ban kissing at official functions to stop the spread of disease.”
The team, who include researchers from Tartu University in Estonia, are now keen to discover more ancient herpes DNA to help them piece together more of the virus’s backstory. When herpes coincides with other illnesses it can occasionally be fatal, and clues as to why may lie in the virus’s genetic history.
Dr Christiana Scheib, a co-author on the study at Cambridge, is hopeful of finding herpes DNA in Neanderthals. “We know most species have their own herpes strains, and to better understand human-Neanderthal interactions and how they shared pathogens, it would be fantastic if someday we could isolate a Neanderthal strain.”