Some of Europe's most well-known historic manuscripts, including the York Gospels, have proven to be biological time capsules for uncovering the 3,500-year history of the sheeppox virus (SPPV).
By extracting DNA from the animal skins used to make the documents' centuries-old parchment, an international team of geneticists, historians, virologists, protein chemists and conservators, led by University College Dublin have provided the first genetic evidence of how this devastating disease plagued European farmers' herds long before the modern era.
A highly contagious disease, sheeppox spreads rapidly and can affect large portions of a flock in a short time.
The disease is particularly dangerous because it can cause very high mortality rates, especially in young animals, and dramatically reduces productivity by damaging wool, meat and milk yields.
"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. It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past," said Louis L'Hôte, PhD candidate at UCD and lead author of the study.
"These genomes help us understand how these pathogens evolved and how they impacted past societies - such as sheeppox virus, which we show has been affecting Eurasian sheep herds for at least three and a half millennia."
In a new study, published in Science Advances, reconstructing over 3,500 years of sheeppox virus evolution, researchers identified traces of the disease in medieval manuscripts, including several of significant historical importance.
Among the works analysed was the 1,000-year-old York Gospels, one of the finest illuminated manuscripts surviving from the early Anglo-Saxon period, and earlier manuscripts such as the Corpus Glossary of Corpus Christi College Cambridge, one of the earliest English dictionaries, and other medieval codices from across Britain and continental Europe.
In several cases, multiple pages from the same manuscript were found to contain sheeppox virus DNA, indicating that infected animals were used in their production.
Because the parchment used in the making of these documents was made from the hides of livestock like sheep, goats, and cattle it serves as a unique bio-archive, preserving the health of the animal at the time of its death centuries ago.
One of the most unexpected findings from the new study was the detection of sheeppox virus on parchment made from calfskin and goatskin, suggesting either rare examples of cross-species infections or that there was contamination during the parchment-making process.
"Parchment making has been considered a vanishing craft, but we are beginning to understand just how much of the past it has retained. 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," said Dr Kevin G. Daly, Associate Professor at UCD School of Agriculture and Food Science and the study's supervising author.
"This kind of exciting, surprising discovery is only possible when researchers from a range of disciplines come together to share their expertise and data - a generosity and trust that collaborative science depends on."
By combining the study of manuscripts with even older samples from Bronze Age sheep teeth, the study reveals that Sheeppox has threatened livestock for over 3,700 years.
Unlike other skeletal material, teeth can preserve genetic evidence of infection over thousands of years, providing a valuable record of past outbreaks.
The research team identified the earliest known detections of sheeppox virus from dental remains recovered from ancient pastoralist settlements in the Eurasian steppe.
By comparing these ancient sequences with modern ones, they estimate that the major lineages of capripoxviruses (sheeppox virus, goatpox virus, and lumpy skin disease virus) diverged between 11,500 and 3,700 years ago.
This timeline aligns with the rise of animal domestication and the major translocation of sheep from the steppe into Europe.
"People around the world are still fighting against this pathogen - there is currently an outbreak of sheeppox in Greece, causing much economic damage," said Louis L'Hôte .
"Ancient genomes can help us understand how these pathogens affecting us today evolved. We find that unlike the smallpox virus, the sheeppox virus genome was very stable over the last few millennia."
Adding: "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."
This study was funded by Taighde Éireann-Research Ireland and the European Research Council, and led by researchers at UCD in collaboration with over 30 Irish and international institutions including 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.
