Researchers say the herpes species that cause modern cold sores spread widely in the wake of Bronze Age migrations, and may have received a boost from the accompanying kissing practice.
Scientists in Cambridge analyzed the first ancient DNA samples of the herpes simplex virus and found that one variant outnumbered all other species about 4,500 years ago, setting the course for its dominance today.
“The variants found in Europe today all share a Bronze Age ancestor,” said Dr. Charlotte Holdcroft, a virologist on the study. “There were variables before that, but they have been replaced, possibly due to human behavior.”
The herpes simplex virus, or HSV-1, infects nearly 4 billion people globally. It is believed to have appeared millions of years ago, before humans separated from their main relatives. But the lack of ancient herpes DNA has left scientists unclear about how it evolved since humans spread out of Africa.
Writing science progressIn this article, the team describes how they examined ancient DNA extracted from nearly 3,000 archaeological sites and found only four individuals – from the United Kingdom, the Netherlands and Russia – who had herpes infection. Together, they span a period of 1,000 years.
The oldest individual was an Iron Age man excavated at a burial site in the Urals, dating back about 1,500 years. Two others were buried in the Cambridge area: a woman in her thirties or forties in the Anglo-Saxon cemetery in Edix Hill, and a man in his late teens or early twenties at St John’s Hospital. The third skeleton of a man in his mid-20s and 30s, with curved teeth and a fondness for smoking an earthen pipe, came from a cemetery on the bank of the Rhine, a possible victim of a French attack on his village in 1672.
Analysis of ancient DNA showed that the herpes virus was remarkably similar to the virus seen today and can be traced back to the Bronze Age. The timing coincides with extensive migrations to Europe from the Eurasia grasslands and a population boom that could have resulted in higher transmission rates.
Scientists suggest that another factor may be at play. 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 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 its transmission.
“If you suddenly have a group of people kissing, and that’s not universal human behaviour, that’s an additional way to spread the virus,” Holdcroft said.
But she said more evidence was needed. “Kissing is one of those behaviors that doesn’t petrify well. The dangers of kissing were certainly obvious to the Romans. Centuries later, Emperor Tiberius tried to ban kissing on official occasions to stop the spread of disease.”
The team, which includes researchers from the University of Tartu in Estonia, is now keen to discover more ancient herpes DNA to help them piece together more of the virus’ backstory. When herpes co-occurs with other diseases, it can sometimes be fatal, and clues to the cause may lie in the genetic history of the virus.
Dr Christiana Shipp, a study co-author in Cambridge, hopes to find herpes DNA in Neanderthals. “We know that most species have their own herpes strains, and to better understand human-Neanderthal interactions and how they shared pathogens, it would be great if we could one day isolate the Neanderthal strain.”
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