Cambridge, Trinity College, MS B.10.5, fol. 62v, the Epistles of St Paul, Ireland/Northumbria, 700–800 CE. Reproduced with kind permission of the Master and Fellows of Trinity College Cambridge
Centuries before anyone thought to look, the skins used to bind some of Europe's most treasured manuscripts—including the 1,000-year-old York Gospels—were quietly recording a history of their own. Buried in that parchment, researchers have now found genetic traces of the highly contagious and fatal sheeppox virus, revealing that it has plagued sheep herds for at least 3,500 years.
Among the works analyzed was the 1,000-year-old York Gospels, the Corpus Glossary of Corpus Christi College Cambridge—one of the earliest English dictionaries—and other medieval codices from across Britain and continental Europe.
Published in Science Advances, the study results show that multiple pages from the same manuscript were found to contain sheeppox virus DNA, indicating that infected animals were used in their production. The researchers also found 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.
The team also combined the manuscript findings with older genetic material pulled from Bronze Age sheep teeth, which can preserve infection evidence over thousands of years. That combination pushed the sheepox timeline back further still: the earliest known traces of sheeppox virus came from dental remains recovered at ancient pastoralist settlements in the Eurasian steppe, showing the disease has threatened livestock for more than 3,700 years.
Comparing ancient and modern viral sequences, the team estimated that the major lineages of capripoxviruses—sheeppox, goatpox and lumpy skin disease virus—split apart somewhere between 11,500 and 3,700 years ago, a window that lines up with the rise of animal domestication and the migration of sheep from the steppe into Europe.
Sheeppox is highly contagious, spreads rapidly and can affect large portions of a flock in a short period of time. The disease is especially harmful in young animals, and it can dramatically reduce productivity by damaging wool, meat and milk yields. But it is not just a disease of the past—sheeppox remains an active threat today, with an ongoing outbreak in Greece currently causing significant economic damage.
“Ancient genomes can help us understand how these pathogens affecting us today evolved,” said the study’s lead author, Louis L'Hôte, a PhD candidate at University College Dublin. “We find that unlike the smallpox virus, the sheeppox virus genome was very stable over the last few millennia. 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 discovery also suggests genetic evidence could be unknowingly hiding in similar archives worldwide.
“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 L'Hôte. “It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past.”