One of the samples of ancient herpes DNA used in the study came from a male of 26-35 years old, excavated near the banks of the Rhine. The man was a fervent smoker of clay pipes. Traces of the habit are visible in multiple places on the teeth, where the hard clay pipe, usually put in the same place in the mouth, has worn the teeth. Credit: Barbara Veselka
As viruses new and old continue to spread at an alarming rate, scientists at the University of Cambridge (UK) have traced the origin of today’s HSV-1 virus strain of facial herpes to the Bronze Age—about 5,000 years ago.
“Every primate species has a form of herpes, so we assume it has been with us since our own species left Africa,” said co-senior author Christiana Scheib, research fellow at University of Cambridge and head of the Ancient DNA lab at Tartu University.
So, what happened around 5,000 years ago that allowed one strain of herpes to overtake all others? According to Scheib and team, the culprit was a new Bronze Age cultural practice imported from the east: kissing.
Garnering samples
Despite its contemporary prevalence among humans, the scientists say ancient examples of HSV-1 were surprisingly hard to find.
“The world has watched COVID-19 mutate at a rapid rate over weeks and months. A virus like herpes evolves on a far grander timescale,” said co-senior author Charlotte Houldcroft, genetic professor at the University of Cambridge. “Facial herpes hides in its host for life and only transmits through oral contact, so mutations occur slowly over centuries and millennia. We needed to do deep time investigations to understand how DNA viruses like this evolve.”
Previously, genetic data for herpes only went back to 1925. But this team managed to find herpes in the remains of four individuals stretching over a thousand-year period. The researchers screened ancient DNA samples from around 3,000 archaeological finds before they were able to secure four herpes hits.
The oldest sample came from an adult male excavated in Russia’s Ural Mountain region, dating from the late Iron Age around 1,500 years ago. The two middle ones came from Cambridge—a female from an early Anglo-Saxon cemetery dating from 6-7th centuries CE, and a young adult male from the late 14th century buried in the grounds of medieval Cambridge’s charitable hospital. The final sample came from a young adult male excavated in Holland who was most likely massacred by a French attack on his village in 1672.
According to their paper in Science Advances, the research team extracted ancient DNA from the roots of the teeth of all four individuals, and compared that data with herpes samples from the 20th century. This allowed the scientists to analyze the differences and estimate a mutation rate—consequently establishing a timeline for virus evolution.
Given the high prevalence of HSV-1 infections in humans today, the researchers expected the virus to be abundant in archaeological teeth—but that was not the case. One reason could be due to sample techniques, i.e. the researchers extracted aDNA from the root of the teeth, but HSV-1 was living elsewhere, like the dental pulp chamber. Another possibility could be that most individuals then—as now—had a latent infection with low HSV-1 copy numbers and/or reduced oral shedding.
However, the researchers say, the most likely reason is a lineage replacement event.
“For a lineage replacement to occur, there must be new diversity that becomes more prevalent than the old strains. This could be due to increased transmissibility due to either pathogen or host-specific factors,” the scientists explain in their paper. “Since we did not detect large-scale changes in the core genomic composition of ancient and modern HSV-1 strains, it is unlikely due to a change in the pathogen genome; rather, HSV-1 may have become more prevalent over time due to changes in human behavior.”
That behavior, the researchers suggest, was kissing. The earliest known record of kissing is a Bronze Age manuscript from South Asia. As with goods and people, the “custom” could have easily traveled westward into Europe from Eurasia.
Next, the researchers want to trace herpes even deeper through time to investigate its infection of early hominins.
“Neanderthal herpes is my next mountain to climb,” said Scheib.