The story of a Medieval European plague is coming into focus through historic manuscripts, but not in the way you might think. Instead of providing mere historical accounts, the animal skins from which these Medieval volumes are constructed provide genetic evidence for reconstructing the 3,500-year story of the sheepox virus (SPPV), which decimated European livestock.

In a recent paper published in Science Advances, an international team of interdisciplinary researchers ranging from geneticists and virologists to historians and conservators explored the history of this pre-modern plague.

The new work combs through Medieval history to reveal the lineages of diseases plaguing modern herds, providing new insight into the viruses threatening modern animal agriculture.

Medieval Texts

Chosen for the work were some of the most important Medieval manuscripts that Europe has to offer, including the millennium-old York Gospels, one of the best surviving examples of an early Anglo-Saxon illuminated manuscript. Another work used in the study was one of the earliest known English dictionaries, the Corpus Glossary of Corpus Christi College, Cambridge. Beyond these notable examples, the team exploited a variety of English and continental European works.

Medieval volumes did not contain paper pages like modern books, but instead, vellum pages made of calfskin, as well as the skins of goats and sheep. Therefore, these works are preserved as hundreds-of-years-old biological specimens for modern geneticists.

SPPV tends to target younger animals, such as the calves from whom vellum is made, and is highly contagious, rapidly spreading through large portions of a herd. While these factors made the disease easier for modern researchers to study via vellum samples, it also made it devastating to wool, meat, and milk production.

Extracting DNA

“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. It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past,” said lead author Louis L’Hôte, PhD candidate at the University of Cambridge, Dublin.

“These genomes help us understand how these pathogens evolved and how they impacted past societies – such as sheeppox virus, which we show has been affecting Eurasian sheep herds for at least three and a half millennia,” L’Hôte added.

With the rapid spread of SPPV across herds, many manuscripts contained SPPV DNA on multiple pages within the same manuscript. Additionally, finding SPPV DNA on pages made from both calf and goat skin marks it as a rare example of cross-species infection.

“Parchment making has been considered a vanishing craft, but we are beginning to understand just how much of the past it has retained. 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,” said supervising author Dr Kevin G. Daly, Associate Professor at UCD School of Agriculture and Food Science.

“This kind of exciting, surprising discovery is only possible when researchers from a range of disciplines come together to share their expertise and data,” Day said, calling this “a generosity and trust that collaborative science depends on.”

Exploring Medieval DNA

The Medieval manuscripts combine with even older surviving biological records, such as teeth, to show the virus reaching back 3,700 years. Between the manuscripts and archaeological finds, the team identified 41 samples containing related viruses.

Along with the goatpox virus and the lumpy skin disease virus, SPPV belongs to a category called capripoxviruses. The new research allowed the team to compare the ancient and modern sequences to determine that the division between the various viruses in the group occurred between 3,700 and 11,500 years ago, around the time animal domestication took hold in Europe as sheep came off the steppe.

“Ancient genomes can help us understand how these pathogens affecting us today evolved. We find that, unlike the smallpox virus, the sheeppox virus genome was very stable over the last few millennia,” L’Hôte concluded. “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.”

The paper, “3,500 years of Sheeppox Virus Evolution Inferred from Archaeological and Codicological Genomes,” appeared in Science Advances on September 2, 2026.

Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.

Sheeppox is a highly contagious, often fatal viral disease that was largely eradicated from much of European livestock in the 20th century. But there is still the occasional regional outbreak, such as the one that afflicted many flocks of sheep in Greece last year. In order to reconstruct how the virus has evolved over the last 3,500 years, scientists extracted and sequenced sheeppox DNA preserved in the animal skins used for the parchment of numerous medieval manuscripts. They reported their findings in a new paper published in the journal Science Advances.

“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. It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past,” said co-author Louis L’Hôte, a graduate student at University College Dublin. “These genomes help us understand how these pathogens evolved and how they impacted past societies—such as sheeppox virus, which we show has been affecting Eurasian sheep herds for at least three and a half millennia.”

Per the authors, the earliest known written evidence of sheeppox infection dates to the first century CE, when Roman accounts described outbreaks of skin lesions ("pustules") in the animals. There are more frequent mentions of deadly outbreaks of "pockes" or "variola" in sheep by the Middle Ages, recorded in various agricultural texts and accounting documents in France, Spain, and England. There seemed to be a decline in outbreaks in 17th-century France, although frequent outbreaks re-emerged in the 18th and 19th centuries, often with high mortality rates in the flocks. Great Britain did not experience a sheeppox resurgence until 1847.

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New evidence for the existence of “lost” ancient medieval manuscripts, long forgotten from memory, is now being uncovered by researchers using agent-based computer simulations.

The findings, reported by Jean-Baptiste Camps and colleagues, relied on a novel approach to uncovering evidence for these long-lost texts: a complexity science approach that allowed them to estimate the volumes of lost ancient literature that once existed, by inferring references to such texts from existing chivalric narratives beginning in the 12th century.

The team’s findings also bring to attention a new concern for historians, since according to their simulations, as much as 60% of all ancient texts from this period, and more than 95% of manuscripts once believed to have existed, may have been lost to time. The findings were recently reported in PNAS Nexus.

Evidence of “Lost” Medieval Manuscripts?

The names we commonly associate with epic tales passed down to us from ancient literature are not the only heroes of yore that existed—they are merely the ones whose stories survived.

For every Gilgamesh, Thor, and King Arthur, it is possible that several more heroic characters from undiscovered ancient epics also exist. However, based on Camps and his team’s findings, they are probably unrecoverable stories, lost to time apart from scant references that occasionally appear in the few surviving manuscripts that have made their way down to us throughout time.

Some of the problems that have contributed to this concerning loss of ancient knowledge are technological. In the days before the invention of the printing press, texts had to be copied manually—a process that led to both innovations, but also errors and inconsistencies as these early copies were made.

From existing copies of surviving ancient texts, scholars can often infer a significant amount of information based on subtle (or in some cases, not-so-subtle) changes that appear from one version to the next. Philologists, researchers who study the structure, historical development, and relationships between languages, refer to the evolutionary “trees” encompassing such texts and their evolution through time as stemmata.

What’s ‘Stemmata’ With You?

Since modern stemmata are based only on existing copies, they lack the full evolutionary history of texts and fail to account for versions that have been forever lost, which may have contained significant differences or additional information.

Jean-Baptiste Camps and his colleagues’ new model has revealed a key discovery: that the early years of a text’s creation, and the number of copies that were made during that time, are of crucial importance to their survival.

As one might guess, the fewer copies that are made, the more endangered the text becomes. However, another implication based on the team’s modeling is that if no copies of the original work are made, all the surviving derivatives generally form what scholars recognize as a subsidiary branch of that manuscript’s family tree.

And therein lies the issue: one that has sobering implications for the preservation of knowledge from ancient times.

Roland’s Unknown Song

As an example, the researchers point to the Song of Roland, an 11th-century account of the Frankish military leader Roland’s deeds at the Battle of Roncevaux Pass. The events in question took place in AD 778, during the reign of Charlemagne, and the account remains the oldest single surviving major work of French literature.

However, the version of the tale we know today comes to us from several different manuscript copies that were made over time. While this speaks to the tale’s popularity in the Medieval world of the 12th to the 16th centuries, it also underscores the fact that its oldest, original versions are probably unknowable to us today.

But how is such knowledge lost to time? Arguably, one of history’s most famous examples involves the famous burning of the library at Alexandria—a story which is itself somewhat contested by modern scholars, in that rather than one catastrophic loss of information resulting from the destruction of a single building, a range of factors over an extended period are more likely to have resulted in the loss of this wealth of knowledge from the ancient world.

This is merely one example; a range of other instances involving random occurrences, accidents, and cataclysmic events point to additional reasons for the fragility of knowledge. One that Camps and his colleagues point to is obvious: the Black Death, which, in addition to raging through Europe and decimating human populations, also likely contributed significantly to the destruction of ancient manuscripts.

Knowledge must be protected, in other words, and the team’s recent findings only underscore how fragile it is—and also how easily it can be lost.

The team’s study, “On the transmission of texts: Written cultures as complex systems,” appeared in PNAS Nexus on July 7, 2026.

Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.