Sheeppox virus DNA found in 1,000-year-old York Gospels parchment

Viral DNA recovered from the 1,000-year-old York Gospels has pushed the known history of sheeppox virus back more than 3,700 years and revealed a pathogen that has barely changed genetically across millennia.

An international team led by University College Dublin detected sheeppox virus DNA on parchment pages of several medieval manuscripts, including the York Gospels, one of the finest surviving illuminated manuscripts from the early Anglo-Saxon period. The study, published in Science Advances, reconstructed more than 3,500 years of sheeppox virus evolution. It marks the first genetic evidence that the disease circulated in European sheep flocks long before the modern era.

Sheeppox is highly contagious and can sweep through a flock rapidly. It kills large numbers of infected animals, especially young sheep, and causes major economic losses through reduced wool, meat, and milk production. A current outbreak in Greece is causing substantial economic damage, according to the study's lead author.

How did medieval books preserve a livestock pathogen?

Before paper became widely available, scribes produced manuscripts from carefully prepared animal hides — sheep, goat, and cattle skins. Those skins can preserve traces of the animal's biological history, including infections present at death. The researchers detected sheeppox viral DNA on multiple pages of several manuscripts, indicating infected animals supplied some of the skins.

The team examined the York Gospels, the Corpus Glossary at Corpus Christi College Cambridge — one of the earliest English dictionaries — and other medieval manuscripts from Britain and continental Europe. An unexpected finding emerged: viral DNA also appeared on calfskin and goatskin parchment. Because sheeppox primarily infects sheep, the researchers propose two explanations — the virus occasionally infected other livestock species, or viral material contaminated skins during parchment production.

"The recording of ancient DNA of pathogens has completely changed our understanding of infectious disease in the past, and here we show that parchment can also preserve animal pathogen DNA," said Louis L'Hôte, PhD candidate at UCD and lead author. "It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past."

What do Bronze Age teeth add?

To extend the timeline beyond the medieval period, the scientists analyzed DNA from sheep teeth dating to the Bronze Age. Teeth protect genetic material for thousands of years and often preserve evidence lost from other skeletal remains.

The team identified the oldest known genetic traces of sheeppox virus in sheep teeth from ancient pastoralist settlements in the Eurasian steppe. Combined with the manuscript data, the evidence confirms the disease has affected livestock for more than 3,700 years.

By comparing ancient and modern viral sequences, the researchers estimated that the main branches of the capripoxvirus family — sheeppox virus, goatpox virus, and lumpy skin disease virus — diverged between 11,500 and 3,700 years ago. That window coincides with livestock domestication and the large-scale movement of sheep from the Eurasian steppe into Europe, movements the authors say may have shaped the virus's long transmission history.

Why does genome stability matter?

Unlike smallpox virus, sheeppox virus has remained remarkably stable genetically over the last few millennia. "We find that unlike the smallpox virus, the sheeppox virus genome was very stable over the last few millennia," L'Hôte said.

That stability implies the genetic changes that made the virus an effective sheep pathogen occurred earlier in its history. Pinpointing them could inform future control strategies against a pathogen that still threatens sheep farming today.

"This might mean that genetic changes before this point were very important to how the sheeppox virus evolved to infect its host, which may help us fight the pathogen in the future," L'Hôte said.

A new archive for disease history

The findings suggest libraries and archives worldwide hold far more disease data than previously recognized. Manuscripts preserved for centuries can supply genetic evidence of livestock outbreaks that left no other records.

"Parchment making has been considered a vanishing craft, but we are beginning to understand just how much of the past it has retained," said Dr. Kevin G. Daly, Associate Professor at UCD School of Agriculture and Food Science and supervising author. "This project shows that parchments not only preserve our cultural history for hundreds of years, but also the landscape of disease in our livestock in the medieval period."

The project brought together more than 30 institutions in Ireland and internationally, spanning genetics, history, virology, protein chemistry, and conservation. Partners included Trinity College Dublin, the Helmholtz Institute for One Health, Université Paris 1 Panthéon-Sorbonne, the University of Leicester, Cambridge University, and the University of Copenhagen. Funding came from Taighde Éireann-Research Ireland and the European Research Council.

The team's approach, combining codicological and archaeological genomes, now offers veterinary science a repeatable method for tracing the emergence and spread of pathogens that remain active today.