Ancient DNA reveals herpes virus coevolved with humans for 2,500 years

A girl died in Italy sometime between 1100 and 600 BC, during the Iron Age. Twenty-six centuries later, scientists would extract her DNA and find something unexpected: the genetic code of a herpes virus, preserved in her bones, telling a story of disease and human biology that had never been read before.

European researchers from Cambridge and University College London have now reconstructed eleven ancient genomes of human herpesvirus 6—HHV-6—by analyzing nearly four thousand skeletal samples from archaeological sites across Europe. What they found rewrites the timeline of how long this virus has lived alongside us. The evidence shows that HHV-6 has been infecting humans for at least twenty-five hundred years, and that during this immense span of time, the virus did something remarkable: it wove itself into our DNA.

Most people encounter HHV-6 in early childhood. About ninety percent of children are infected before age two, usually with mild symptoms. The virus causes roséola infantis, sometimes called the sixth disease, and it remains the leading cause of febrile seizures in infants. In the vast majority of cases, the infection passes quietly, and the virus settles into a dormant state within the body, where it can remain for a lifetime. But in a small fraction of the population—roughly one percent worldwide—something different happened. The virus didn't just hide. It integrated itself directly into the human genome, becoming part of the inherited code that parents pass to children. These people carry viral DNA in every cell of their bodies, a genetic inheritance as real as eye color or height.

For decades, scientists suspected this integration was ancient. They knew it happened. They could see it in modern genomes. But they lacked the archaeological proof. The new study provides it. The oldest known case came from that Iron Age girl in Italy. Medieval remains from England, Belgium, and Estonia yielded more examples. The Belgian site of Sint-Truiden showed the highest concentration, with both HHV-6A and HHV-6B circulating in the same community simultaneously. In England, multiple individuals carried the hereditary form of HHV-6B—the oldest known cases of integrated human herpesvirus in the archaeological record.

The two variants of the virus followed different evolutionary paths. HHV-6A appears to have lost the ability to integrate into human DNA relatively early in its history with us. HHV-6B retained that capacity and continued to do so across millennia. By comparing the ancient genomes with modern genetic data, researchers could pinpoint the exact chromosomal locations where the viruses had inserted themselves thousands of years ago, then trace how those insertions were passed down through countless generations. It is a genetic fingerprint of coevolution—virus and host, locked in a relationship so old that neither can be fully understood without the other.

Meriam Guellil, the lead researcher from the University of Vienna's Department of Evolutionary Anthropology, noted the difficulty of the work. Finding these ancient viral sequences required extraordinary effort because they represent such a small fraction of the total DNA in skeletal remains. The fact that only about one percent of the population carries inherited copies made the search exponentially harder. Yet the team succeeded, and their data now extends the documented history of HHV-6 in Europe back to between the eighth and sixth centuries before Christ.

The discovery carries implications beyond historical curiosity. Charlotte Houldcroft from Cambridge's Department of Genetics pointed out that the presence of integrated HHV-6B has been associated with angina and heart disease. The hereditary forms of both HHV-6A and HHV-6B are more common in the United Kingdom today than elsewhere in Europe—and this study provides the first evidence that long-term carriers existed in Britain in medieval times, suggesting a lineage of inheritance stretching back centuries. What began as a childhood infection, mild and forgettable, became woven into the fabric of human biology itself, passed down through families and populations, shaping health outcomes across generations. The virus did not kill the girl from Iron Age Italy. It simply stayed, became part of her, and through her descendants, became part of us.