The herpes variants that cause modern cold sores became widespread in the wake of the Bronze Age migrations and may have received a boost from the accompanying practice of kissing, researchers say.
Cambridge scientists analyzed the first ancient samples of herpes simplex virus DNA and found that one variant outcompeted all others about 4,500 years ago, setting the course for its current dominance.
“Variants in Europe today share a Bronze Age ancestor,” said Dr Charlotte Houldcroft, a virologist at the study. “There were variants before this, but they have been replaced, probably due to human behavior.”
Herpes simplex virus, or HSV-1, infects nearly 4 billion people worldwide. It is believed to have emerged millions of years ago, before humans split from their primate relatives. But the lack of ancient herpes DNA has left scientists unsure of how it has evolved since humans spread out of Africa.
Writing in Science Advances, the team describes how they examined ancient DNA recovered from around 3,000 archaeological sites and found only four individuals (from the UK, the Netherlands and Russia) who had herpes infections. Together, they span a period of 1,000 years.
The skeleton found in the burial ground at St John’s Hospital in Cambridge. Photography: brochure
The oldest individual was an Iron Age man excavated from a burial site in the Ural Mountains, dating back to about 1,500 years ago. Two other people were buried in the Cambridge area: a woman in her 30s or 40s in an Anglo-Saxon cemetery at Edix Hill, and a man in his late teens or 20s at St John’s Hospital. A third skeleton, that of a man in his 20s and 30s, whose bent teeth betrayed a penchant for clay pipe smoking, came from a burial on the banks of the Rhine, a likely victim of a French attack on his town in 1672. .
Analysis of 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 large migrations into Europe from the Eurasian grasslands and a population boom that could have increased transmission rates.
But another factor may have come into play, the scientists suggest. The oldest 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 transmitted from mother to child, limiting transmission.
“If you suddenly have a group of people kissing, which was not universal human behavior, that’s an additional way to spread the virus,” Houldcroft said.
But he said more evidence was needed. “Kissing is one of those behaviors that don’t fossilize well. The risks of kissing were obvious to the Romans. Centuries later, Emperor Tiberius tried to ban kissing at official functions to stop the spread of the disease.”
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The team, which includes researchers from the University of Tartu in Estonia, is now set to uncover DNA from the oldest herpes to help piece together more of the virus’s backstory. When herpes coincides with other diseases, it can occasionally be fatal and the clues as to why may be in the genetic history of the virus.
Dr Christiana Scheib, co-author of the study in Cambridge, hopes to find herpes DNA in Neanderthals. “We know that most species have their own strains of herpes, and to better understand the interactions between humans and Neanderthals and how they shared pathogens, it would be great if one day we could isolate a Neanderthal strain.”