Medieval manuscripts are "biological time capsules" for deadly sheeppox virus

For instance, last year we reported on research that used microbial DNA analysis of human remains to identify the likely pathogens that killed many soldiers in Napoleon’s army in 1812. Two pathogens in particular stood out: Salmonella enterica, which causes paratyphoid fever, and Borrelia recurrentis, which is transmitted by body lice and causes relapsing fever. Both are consistent with written contemporary accounts.

Evolution of a virus

The team collected samples from medieval manuscripts housed in collections at Yale University, Cambridge University, Corpus Christi College, University College Dublin, the Lambeth Palace Library, and Trinity College, among others. Those works included pages from a 15th-century Speculum Historiale; the 15th-century Clairvaux manuscripts; several 9th-century gospel text fragments; the 9th-century Achadeus Psalter; the early 11th-century Trinity Gospels; the Lambeth Bible; and the 1,000-year-old York Gospels.

Multiple pages, often from the same manuscript, were found to contain DNA from the sheeppox pathogen, which means infected animals were likely used to make the parchment—and thus, that medieval flocks experienced frequent outbreaks of sheeppox. The authors were surprised when they also found evidence of the sheeppox virus on parchment made from calfskin and goatskin, suggesting either cross-species infection or contamination when the parchment was being made.

The team also extracted DNA from Bronze Age sheep teeth collected at settlement sites in Russia and Central Kazakhstan, since teeth can preserve DNA evidence of infection over thousands of years. After comparing those ancient sequences with the medieval ones, the authors concluded that the sheeppox virus diverged from the goatpox and lumpy skin disease viruses (all members of the Capripoxvirus family) between 11,500 and 3,700 years ago. That coincides roughly with the domestication of animals in Europe. All told, the team recovered 21 ancient genomes from 1700 BCE to early modern Europe.

“Parchment making has been considered a vanishing craft, but we are beginning to understand just how much of the past it has retained,” said co-author Kevin G. Daly, also of UCD. “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. 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.”

DOI: Science Advances, 2026. 0.1126/sciadv.aeh3571  (About DOIs).