The spread of the modern-day cold sore has been traced back to the Bronze Age and linked the rise of kissing, according to a new study.
Researchers said this migration led to both denser populations, which drove up rates of transmission, and new cultural practices being imported from the east, including kissing.
The earliest known record of kissing comes from a Bronze Age manuscript from South Asia.
The custom becoming widespread coincided with the spread of HSV-1, which can be spread orally, according to the study published in the journal Science Advances.
Scientists at the University of Cambridge led the research and become the first to uncover and sequence ancient genomes of the virus, which currently infects some 3.7 billion people worldwide.
Previously, genetic data for herpes only went back to 1925, but the team hunted down four samples from human remains dating over a 1,000-year period.
By comparing ancient samples with ones from the 20th century, they were able to develop estimates for a timeline of evolution.
Co-senior author Dr Christiana Scheib, research fellow at St John’s College, Cambridge, and head of the ancient DNA lab at Tartu University, said: “Every primate species has a form of herpes, so we assume it has been with us since our own species left Africa.
“However, something happened around five thousand years ago that allowed one strain of herpes to overtake all others, possibly an increase in transmissions, which could have been linked to kissing.”
Samples used in the study were taken by extracting viral DNA from the roots of the teeth of four individuals.
Herpes often flares up with mouth infections, and at least two of the individuals had suffered gum disease, a third of whom smoked tobacco.
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 others were a female excavated from an early Anglo-Saxon cemetery in Cambridge, a young adult male from the late 14th century also in Cambridge, and another young adult male likely from 17th century Holland.
Dr Charlotte Houldcroft, co-senior author, added: “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.
“Facial herpes hides in its host for life and only transmits through oral contact, so mutations occur slowly over centuries and millennia.
“We need to do deep time investigations to understand how DNA viruses like this evolve.”
The World Health Organisation says two thirds of the global population under the age of 50 now carry HSV-1.
Cold sores are contagious from the moment you first feel tingling, warns the NHS. It also advises against kissing babies when you have a cold sore as it can lead to neonatal herpes, which is very dangerous to newborn babies.
Cold sores are mostly a source of discomfort or embarrassment for those suffering from them, but coupled with other health complications such as sepsis or even Covid, the virus can be deadly.
Newborn babies, pregnant women and people with a weakened immune system may be referred to hospital for advice or treatment, says the NHS. In 2018, two new mothers died of HSV-1 infection following caesarean births.
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