The Ancient DNA of a Deadly Animal Virus Has Been Lurking in Medieval Manuscripts for Centuries, Researchers Find

Sheep pox is a highly contagious, often fatal disease that can devastate entire herds. Now, scientists have found traces of the virus in historic manuscripts, suggesting that it has been plaguing European farmers for thousands of years. The findings, published this month in the journal Science Advances, offer new insights into the origins and evolution of the deadly virus.

But they also indicate that animal skin parchment may be an untapped tool for exploring the history of livestock pathogens. For the study, researchers collected samples from historic medieval manuscripts from across Britain and continental Europe, held in the collections of the University of Cambridge, Yale University, the Austrian National Library and the Lambeth Palace Library, among others. Dating from the early eighth to the 14th century C.E., the manuscripts included the 1,000-year-old York Gospels, a richly illustrated masterpiece of the early medieval era, and the Corpus Glossary, an early English dictionary made around 800 C.E.

The researchers also investigated an annotated copy of the Epistles of St. Paul created around 700 C.E., and a 15th-century section of the encyclopedic Speculum Majus, compiled by Vincent of Beauvais. In a surprising twist, sheep pox virus DNA showed up not only in parchment made from sheepskin but also in pages made from calf and goat skins, as well as paper.

This discovery suggests either cross-species infections or viral contamination during the parchment-making process. For instance, the researchers note, the virus may have been introduced via the animal-derived gelatin or glue that was commonly used in the period to make paper stronger and smoother. The manuscripts suggest that the sheep pox virus has been infecting European livestock for at least 3,500 years.

The scientists also found traces of the virus in sheep teeth from Bronze Age pastoralist settlements in Russia and Central Kazakhstan, pushing its known history back another two centuries, to roughly 3,700 years. All told, the researchers recovered 21 ancient sheep pox virus genomes dating from approximately 1700 B.C.E. to 1917 C.E. Researchers recently discovered that scribes in medieval Europe sometimes wrapped their books in the skins of harbor seals, harp seals and bearded seals.

The skins were likely obtained through trade. The team compared the ancient viral DNA with modern samples, which allowed them to construct a genetic “family tree” showing how different sheep pox virus lineages are related and how they evolved over thousands of years. Their analysis suggests that the major lineages of capripoxviruses—sheep pox virus, goat pox virus and lumpy skin disease virus—began diverging from a common ancestor between 11,500 and 3,700 years ago, around the same time humans were moving and managing livestock in new ways.