Some of Europe’s most famous medieval manuscripts, including the York Gospels, have revealed an extraordinary secret hidden within their pages. Scientists have discovered ancient viral DNA preserved in animal skins used to make parchment, opening a new window into the 3,500-year history of the sheeppox virus (SPPV).
The discovery was made by an international research team led by University College Dublin (UCD). By analyzing scrolls from centuries-old documents, researchers have discovered the first genetic evidence that this destructive disease was spreading in European sheep herds long before modern times.
Smallpox is highly contagious and can spread through a herd with alarming speed. It can kill large numbers of infected animals, particularly young sheep, while causing significant economic losses by reducing the production of wool, meat and milk.
Ancient manuscripts preserve DNA from deadly viruses
Published in Scientific advancesthe new study reconstructs more than 3,500 years of chickenpox virus evolution. Researchers have identified viral DNA in several historically significant medieval manuscripts, revealing that documents preserved for their cultural significance may also contain valuable biological evidence.
Among the manuscripts examined were the 1,000-year-old York Gospels, considered one of the finest illuminated manuscripts of the early Anglo-Saxon period. The researchers also studied older works, including the Corpus Glossary of Corpus Christi College, Cambridge, one of the first English dictionaries, as well as other medieval manuscripts from Britain and continental Europe.
The secret lies in the parchment itself. Before paper became widely available, manuscripts were often produced from carefully prepared animal hides, including sheep, goat, and cattle hides. These materials can preserve traces of an animal’s biological history, including evidence of infections present at the time of death.
In several manuscripts, researchers detected sheeppox virus DNA on several pages. These results indicate that infected animals provided some of the skins used to produce the documents.
One particularly surprising discovery involved viral DNA found on calfskin and goatskin parchments. Since pox primarily infects sheep, the findings raise two possibilities: the virus may have occasionally infected other species of livestock, or viral material may have contaminated the hides during parchment production.
Historical books become archives of unexpected illnesses
“Recording ancient DNA from pathogens has completely changed our understanding of infectious diseases in the past, and here we show that parchment can also preserve the DNA of animal pathogens. It is possible that archives and libraries around the world also contain genetic traces of outbreaks in animals in the past,” said Louis L’Hôte, a doctoral student at UCD and lead author of the study.
“These genomes help us understand how these pathogens evolved and how they impacted past societies – like sheepskin virus, which we show has affected Eurasian sheep herds for at least three and a half millennia.”
The findings suggest that libraries and archives may hold much more information about historical diseases than previously thought. Manuscripts that have survived for hundreds of years could provide genetic evidence of livestock epidemics that left few other records.
“Scroll making has been considered a dying craft, but we are beginning to understand how much of the past it has preserved. This project shows that scrolls not only preserve our cultural history for hundreds of years, but also the disease landscape of our livestock in medieval times,” said Dr Kevin G. Daly, associate professor in UCD’s School of Agriculture and Food Sciences and supervising author of the study.
“This kind of exciting and surprising discovery is only possible when researchers from diverse disciplines come together to share their expertise and data – a generosity and trust that collaborative science depends on.”
The project brought together specialists in genetics, history, virology, protein chemistry and conservation, allowing the team to study the manuscripts from a historical and biological perspective.
Ancient sheep teeth reveal 3,700 years of disease
Medieval manuscripts were only part of the investigation. To trace the disease further into the past, scientists also examined DNA recovered from sheep teeth dating back to the Bronze Age.
Teeth are particularly useful for studying ancient infections because they can protect genetic material for thousands of years, often preserving extinct evidence of other skeletal remains.
Researchers have identified the oldest known genetic traces of clavate virus in sheep teeth recovered from ancient pastoral settlements on the Eurasian steppe. Combined with the manuscript’s findings, this evidence shows that the disease has affected livestock for more than 3,700 years.
To study how the virus developed, the team compared ancient viral DNA with genetic sequences from modern viruses. Their analysis suggests that the main branches of the capripoxvirus family (sheeppox virus, goat pox virus, and lumpy skin disease virus) separated from each other between 11,500 and 3,700 years ago.
This estimated timeline coincides with major changes in human history, including the domestication of livestock and the large-scale movement of sheep from the Eurasian steppe to Europe. These movements may have played an important role in the virus’s long history of transmission.
A deadly virus that has remained virtually unchanged for thousands of years
One of the study’s most striking findings is how little genetic change the ringworm has undergone over the past several thousand years. Unlike some other viruses, its genome appears to have remained remarkably stable despite its long history of infecting livestock.
Understanding this stability could help scientists identify the genetic changes that initially allowed the virus to become an effective pathogen for sheep.
The discovery also has immediate relevance. Smallpox remains a serious threat to livestock production, with outbreaks continuing to cause significant economic damage.
“People around the world continue to fight against this pathogen. There is currently a smallpox epidemic in Greece, causing a lot of economic damage,” said Louis L’Hôte.
“Ancient genomes can help us understand how these pathogens that affect us today evolved. We find that unlike the smallpox virus, the smallpox virus genome was very stable over the past few millennia.”
L’Host added: “This could mean that genetic changes prior to this point were very important in how the clavate virus evolved to infect its host, which could help us fight the pathogen in the future.”
By discovering viral DNA in medieval manuscripts and prehistoric animal remains, researchers have demonstrated a powerful new way to study the history of infectious diseases. Their work suggests that materials preserved for entirely different purposes may hold valuable clues about the emergence, spread, and evolution of pathogens that continue to affect the world today.
The research was funded by Taighde Éireann-Research Ireland and the European Research Council. Led by UCD, the project involved more than 30 institutions in Ireland and abroad, including Trinity College Dublin, the Helmholtz Institute for One Health, Université Paris 1 Panthéon-Sorbonne, the University of Leicester, the University of Cambridge and the University of Copenhagen.
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