Preservation of DNA in the teeth of humans dating back as far as 1,500 years has revealed the ancient origins of the ubiquitous strain of the herpes virus that causes cold sores.
Genomic data suggest that herpes simplex virus type 1 (HSV-1), which today infects around 3.7 billion people worldwide, emerged and proliferated around 5,000 years ago. And perhaps it coincided with a new cultural phenomenon that arose and spread at the same time: the smooching of his boo (or boos).
“The world has seen COVID-19 mutate at a rapid rate over weeks and months. A virus like herpes evolves on a much longer timescale,” said geneticist Charlotte Houldcroft of the University of Cambridge in the UK.
“Facial herpes hides in its host for life and is only transmitted by oral contact, so mutations occur slowly over centuries and millennia. We need to do extensive research to understand how viruses DNA like this evolves. Previously, genetic data on herpes only goes back as far as 1925.”
The herpes family has a wide and long history, spanning several species and dating back millions of years. Of the 115 herpes viruses currently known to us, only eight infect humans. Herpes simplex virus 1 (HSV-1) is the most common of these, associated with cold sores. The strain associated with genital herpes, HSV-2, affects about half a billion people.
Infection with either strain is lifelong; there is currently no known cure, although outbreaks can be treated and managed.
How HSV-1 became the dominant human strain is a mystery and surprisingly difficult to trace. A team of researchers therefore decided to take a closer look at the ancient remains.
As DNA sequencing has become faster and cheaper, archaeologists have in recent years built up DNA libraries extracted from ancient remains. From these libraries, the researchers searched for traces of HSV-1 in the archaeological record – and found it extremely rare.
“We sifted through ancient DNA samples from around 3,000 archaeological finds and only got four cases of herpes,” said genomics scientist Meriam Guellil from the University of Tartu in Estonia.
These four individuals spanned a period of a thousand years. The most recent was a young man in the Netherlands, who was probably massacred during a French raid on his village in 1672. The wear on his teeth suggested he was a heavy smoker who used a clay pipe.
Two of the people were from Cambridge in the UK. One was a young adult man from the late 14th century, who was buried on the grounds of a medieval charity hospital. His teeth showed significant signs of horrible dental abscesses. The other, a grown woman, lived and died in Cambridgeshire around the 6th to 7th centuries, and her teeth also showed signs of gum disease.
The oldest remains were those of an adult male from Russia who lived and died around 1,500 years ago. Since HSV-1 tends to spread when the patient has an oral infection, it is not very surprising to find traces of the virus in people with gum disease, abscess or tobacco.
With just these four cases, the team was able to sequence the herpes DNA, examine the differences between the four cases, and determine a mutation rate for the current strain of HSV-1.
This returned a timeline suggesting that the form of HSV-1 that afflicts the world today emerged in the Bronze Age, after humans migrated from the steppe grasslands of Eurasion to Europe, producing a population boom. .
“Every species of primate has some form of herpes, so we assume it has been around since our own species left Africa,” said archaeologist Christiana Scheib from the University of Cambridge and the University of tartu.
“However, something happened about 5,000 years ago that allowed one strain of herpes to overtake all others, possibly an increase in transmissions, which could have been linked to kissing.”
The history of the romantic kiss is murky, but previous research has shown that it’s not universal among humans. This same research found that the more socially complex a culture, the higher the frequency of romantic kisses. As humans migrated, spread and settled in the Bronze Age, it’s possible that kissing also became more common.
Without a clear method to trace the dawn of tonsil hockey, speculation remains strictly hypothetical. Even conclusions about the origins of HSV-1 remain open to some tweaking, given the challenges of identifying the virus in ancient bone.
“Our work therefore highlights the need for broader coverage of modern HSV-1, particularly in regions such as Asia and Africa, as well as additional observations provided by aDNA samples,” the researchers wrote in their paper.
“Other ancient genomes, for example, from the Neolithic period, could further revise our understanding of the evolutionary history of this now ubiquitous pathogen and continue to inform the nature of its association with human hosts.”
The research has been published in Scientists progress.