Medieval manuscripts preserve genetic traces of a sheep disease that has threatened herds across Eurasia for more than 3,700 years, according to a new study.
Researchers recovered ancient DNA from sheeppox virus, or SPPV, in animal skins used to make parchment. The team studied manuscripts from Britain and mainland Europe, along with older remains from Bronze Age sheep. Together, the samples provide a record of SPPV evolution from about 1700 BCE to the Early Modern period.
Sheeppox is highly contagious and spreads fast through flocks. The disease often kills young sheep and reduces wool, meat and milk production. Such losses threatened food supplies and farming communities.
The study, published in Science Advances, reports 21 new ancient SPPV genomes. Several came from medieval parchment, including material linked to important English manuscripts.
One sample came from the roughly 1,000-year-old York Gospels, a major illuminated manuscript from early Anglo-Saxon England. Researchers also found viral DNA in parchment linked to the Corpus Glossary of Corpus Christi College, Cambridge, one of the earliest English dictionaries.
Some manuscripts held SPPV DNA on several pages. The pattern suggests infected animals supplied skins for parchment production. Parchment makers prepared these skins from livestock such as sheep, goats and cattle, leaving biological traces behind.
The findings also raised questions about the virus’s host range. Researchers detected SPPV DNA on calfskin and goatskin parchment. These traces might reflect rare infections in other animals or contamination during skin processing.
Parchment therefore serves as more than a record of human writing. Its animal origins also preserve evidence about livestock health at the time of slaughter. Libraries and archives hold vast amounts of old parchment, offering more material for future study.
The team pushed the history of sheeppox further back by examining ancient sheep teeth from pastoralist settlements on the Eurasian steppe. Teeth often preserve DNA from past infections for thousands of years. The oldest SPPV evidence in the study dates to the Bronze Age, around 1700 BCE.
Genetic comparisons also helped place SPPV within the wider capripoxvirus group. The researchers estimate that the main lineages leading to sheeppox virus, goatpox virus and lumpy skin disease virus split between about 11,500 and 3,700 years ago.
This period overlaps with major changes in sheep farming. Domestication expanded, and sheep moved from the Eurasian steppe into new regions, including Europe. The timing links early virus history with shifts in sheep populations and farming practices.
The ancient genomes also point to long-term stability in SPPV. Unlike smallpox virus, sheeppox virus showed little genetic change across the period covered by the study. Some gene losses linked to SPPV and goatpox virus were already present in the oldest genomes examined.
The disease still affects sheep farms today. An outbreak in Greece has caused economic losses, showing how a virus with an ancient history continues to threaten livestock.
Ancient viral DNA lets researchers compare past and present strains. The new study shows how parchment, alongside archaeological animal remains, preserves a record of disease long after outbreaks disappeared from written history.
