Medieval parchment has become a record of sheeppox virus
Medieval manuscripts kept in European libraries have yielded an unexpected form of infectious-disease evidence: viral DNA preserved in parchment made from animal skin. In documents including the 1,000-year-old York Gospels, researchers detected traces of sheeppox virus, a highly contagious pathogen that still threatens sheep flocks today. The finding pushes the genetic record of the virus deep into the past and links cultural artifacts to the history of livestock disease.
The work matters because parchment was made from hides, and hides carry biology. When an infected animal died and its skin was processed for writing material, fragments of pathogen DNA could survive in the finished pages. In several manuscripts, viral DNA appeared on multiple pages, a pattern that points to infected animals being part of the parchment supply chain rather than a single isolated contamination event. The same logic turns manuscripts into accidental archives of animal health.
One particularly striking detail came from parchment made of calfskin and goatskin. Because sheeppox virus primarily infects sheep, those samples raise two possibilities: the virus may have crossed into other livestock species on occasion, or viral material may have reached the skins during parchment production. Either way, the result expands the historical trail left by a pathogen that has shaped sheep farming for millennia.
Bronze Age teeth extend the timeline to more than 3,700 years
The manuscript evidence did not stand alone. To push the timeline farther back, the investigators also examined DNA from sheep teeth dating to the Bronze Age. Teeth are unusually valuable in ancient DNA research because they can shield genetic material for thousands of years, often after softer tissues have vanished completely.
Those teeth carried the oldest known genetic traces of sheeppox virus recovered so far. Combined with the parchment findings, the data show that the disease has affected livestock for at least 3,700 years. That is a long evolutionary runway for a virus that remains economically damaging in the present day, especially in regions where outbreaks still sweep through sheep populations.
A single sentence captures the clinical and agricultural consequence: the virus has outlasted kingdoms, scripts, and the manuscripts that now preserve its DNA.
A remarkably stable viral genome across millennia
The genetic story is not one of rapid viral churn. One of the most consequential findings was how little the sheeppox virus genome appears to have changed over several thousand years. Compared with many pathogens that accumulate visible genomic drift, this virus has remained remarkably stable. That stability may help narrow the set of mutations that mattered most when the virus first adapted to sheep as a host.
The researchers compared ancient viral sequences with modern ones and estimated that the main branches of the capripoxvirus family — sheeppox virus, goatpox virus, and lumpy skin disease virus — split sometime between 11,500 and 3,700 years ago. The timing overlaps with major shifts in livestock management and the movement of sheep from the Eurasian steppe into Europe. Those human-driven animal movements likely helped shape the virus’s long spread across regions and herds.
In practical terms, a stable genome can be both a clue and a warning. It suggests that some of the most important host-adaptation steps happened early, before the virus reached the long historical phase captured in the study. It also means modern outbreaks may be driven by a pathogen lineage that has retained the same broad biological strategy for a very long time.
What parchment, libraries, and virology now share
The project was built on unusually broad collaboration, bringing together genetics, history, virology, protein chemistry, and conservation science. That combination made it possible to read the manuscripts as both cultural objects and biological specimens. It also opens a new route for disease history: archives may contain pathogen DNA from animals that lived and died centuries ago, even when no veterinary record survives.
The lead investigator described ancient DNA work as having changed how infectious disease is understood in the past, and the parchment findings extend that approach beyond bones and sediments. Libraries and archives may hold far more biological history than once assumed. Manuscripts that survived because they were treasured for their text may also preserve the disease burden of the animals that supplied their pages.
Why the finding still matters for livestock today
Sheeppox remains a serious threat to animal health and agricultural economies. The disease can spread rapidly through a flock, killing many infected animals, particularly young sheep, while also reducing wool, meat, and milk production. Current outbreaks still cause substantial financial harm, and the paper links that modern burden to a pathogen lineage with a very long evolutionary past.
The study also has direct relevance for outbreak science. Ancient genomes can reveal which parts of a pathogen’s history were stable and which changes likely mattered most for host infection. For a livestock virus still causing damage today, that information may help scientists refine how they think about emergence, persistence, and control.
A current outbreak in Greece, cited in the study, gives the historical findings a sharper present-day edge. Ancient DNA is not just an archaeological curiosity here; it is a way to understand a pathogen that remains active in the real world.
A new use for old materials
The broader implication is simple and unusual: materials preserved for art, religion, or scholarship may also preserve the biology of the animals that made them. Medieval parchment has now joined Bronze Age teeth as a source of viral history, and both point to the same conclusion — sheeppox virus has been circulating among Eurasian sheep for far longer than written veterinary history could show.
The study was supported by Taighde Éireann-Research Ireland and the European Research Council, and it drew on more than 30 institutions in Ireland and internationally. Its central message is concrete rather than speculative: old manuscripts can carry more than text, and the DNA they preserve can reshape what is known about enduring livestock pathogens.