Scientists have sequenced the genome of facial herpes, a virus that has infected the majority of humans alive today, for the first time using ancient DNA preserved in people who lived many centuries ago, reports a new study.
The findings shed new light on the origin and spread of this extremely common virus, known as herpes simplex 1 (HSV-1), and potentially open a window into the rise of kissing as a sign of affection during the Bronze Age.
HSV-1 is orally transmitted and can lead to facial cold sores, in contrast to herpes simplex 2, or genital herpes, which is sexually transmitted. Its ubiquity in humans—about 67 percent of the global population under 50 has HSV-1—is just one of many successes for the herpes virus, which has evolved strains that have infected primates, fish, corals, and all manner of other lifeforms for many millions of years.
Scientists have now traced the genetic signatures of the virus back in time using the teeth of four individuals infected with facial herpes: An adult man who lived at least 1,500 years ago near Russia’s Ural mountains, a woman who lived at roughly the same time and who was buried near Cambridge, United Kingdom, a man who was also buried in a Cambridge cemetery about 1,000 years later, and a pipe-smoking man in Holland who was probably massacred in 1672 during a French attack on his town.
Prior to this study, the oldest HSV-1 genome that had been sequenced belonged to a man who lived in New York in 1925, so the new results provide a much broader picture of its movements across time. As a result, the researchers discovered that the dominant version of HSV-1 likely emerged about 5,000 years ago and may be “potentially linked to the introduction of new cultural practices such as the advent of sexual-romantic kissing,” according to a study published on Wednesday in Science Advances.
“At that time, something in either the herpes genome itself, or in human behavior and the transmission of it, changed, which allowed this to outcompete the previous strain,” said Christiana Scheib, a research fellow at St. John’s College, University of Cambridge, and the senior author of the study, in a call
“Normally, herpes is passed from parent to offspring, and that keeps it relatively stable,” added Scheib, who is also head of the Ancient DNA lab at Tartu University. “But when you start introducing a behavior, like romantic kissing, where you’re transferring to somebody outside of your immediate family group, it could be one explanation for why these strains outcompeted [others].”
Scheib emphasized that further investigations of ancient smooches as a vector for HSV-1 should get input from anthropologists, historians, and other interdisciplinary experts. Her team, composed of geneticists, point to some historical references that could help corroborate the connection, including a Bronze Age Vedic text from South Asia and a Roman-era ban kissing issued by Emperor Tiberius, but note that it is far from a universal custom.
“It's a very enticing explanation, but it may not be the case,” Scheib said of the kissing connection. “It could have also been due to something in that strain that made it more fit and more easily transmitted. It could have been just because of the sheer population dynamic changes in the early Bronze Age, with population movements into Europe. You can also get it from sharing drinking vessels and other forms of contact.”
Regardless of how the current HSV-1 strain flourished, it has now outpaced its rivals and infected billions of people across the world. The DNA extracted from the four individuals in this study supports a relatively modern origin for this dominant strain, dating back about 5,000 years, which was proposed in a 2020 study, in contrast to previous research that suggested it dates back tens of thousands of years to human migrations out of Africa. Facial herpes certainly did exist during those prehistoric times, but the new research found it was probably a different strain from the one that is common now.
To better understand the history of HSV-1, Scheib hopes that she, or some other lucky researcher, will be able to find traces of facial herpes in humans—or perhaps, Neanderthals–that lived tens of thousands of years ago. By comparing these ancient herpes genomes to modern strains, they might be able to chart out the course of the virus’s evolution across human history.
“I'd love to get something older,” Scheib said. “If we get Neandertal herpes, that would be really interesting” in part because “we know [humans and Neanderthals] interbred.”
“When people meet, they share pathogens so it'd be really interesting to see how that dynamic played out, around 45,000 or 50,000 years ago,” she concluded. “What were those earlier human strains like? Were they more similar? Were they different? Were they sharing them? If we're gonna pursue it, that would be the next interesting place to go.”