A 3,700-Year-Old Virus Hiding in a Medieval Book Just Killed 500,000 Animals

4 min readHere’s what you’ll learn when you read this story:Researchers who sampled ancient and medieval parchment found the DNA of the sheeppox virus, which devastated herds in the past and continues to do so even today.Based on their analysis, which also extended to Bronze Age sheep teeth, the scientists were able to trace the evolution of the virus back at least 3,700 years.It’s likely that sheeppox epidemics first broke out among the pastoral peoples of the Caucasian and Eastern European steppes through trade and contact between herds.In medieval Europe, it was often thought that sick livestock were the victims of witches who cast spells on them after dark. But what was believed to be black magic was actually the work of microbes. The sheeppox virus, a relative of the human smallpox virus, devastated entire herds, and it remained trapped in skins used to make parchment. That parchment ended up being put to use in the form of pages of religious manuscripts, which are revealing the history of something much less holy.Hiding in some of the most famous European manuscripts from the Middle Ages is genetic evidence of a pathogen that was once mistaken for witchcraft: sheeppox. Affected animals showed symptoms that included fever, loss of appetite, eye discharge, and lesions on parts of the body not covered in wool. Their mouths, trachea, and lungs were also attacked by the virus, as well as their urogenital and digestive systems. The virus also spread rapidly. Herds that hadn’t been exposed before could suffer a 75-90% loss, which meant huge economic losses. Even in sheep that survived, milk, wool, and meat production were affected, with parchment made from the skin sometimes blotched by lesions. And sheeppox never vanished. Just this year, an outbreak in Greece has claimed the lives of nearly 500,000 animals and threatens its cheese industry.While vaccines for sheeppox do exist, that was an impossibility when the York Gospels were written with ink on sheepskin parchment a thousand years ago. The pages of these and other historical documents were examined by a team of researchers led by Louis L’Hôte of the Molecular Population Genetics Lab at University College Dublin. Through sampling from ancient and medieval manuscripts, including the Corpus Glossary and one of the earliest known English dictionaries, the researchers were able to trace the evolution of this virus back over 3,500 years. An analysis of Bronze Age sheep teeth extended that timespan to at least 3,700 years. The preserved teeth recovered from what were once pastoralist settlements in the Eurasian steppe, as far as the Altai mountains in Siberia, are now the earliest known evidence of the virus.“By the Bronze Age period, domestic sheep herds of the Eurasian steppe region were afflicted by a pathogen that today is highly infectious and virulent,” L’Hôte said in a study recently published in Science Advances. “Yersinia pestis, the bacterial agent of the plague, has also been detected in sheep from this region and period, suggesting that herding societies in the steppe may have contended with a diverse burden of [livestock] diseases.”Also known as Capripoxvirus sheeppox, this disease is closely related to the variola virus that causes smallpox in humans. It’s one of three Capripoxvirus variants, along with the goatpox virus, which attacks goats, and the lumpy skin disease virus, transmitted by insects to cattle and domestic water buffalo. Sheeppox first appears in written records from Rome in the first century C.E. Writer Lucius Columella describes skin lesions on animals as “pustules” in his works entitled On Agriculture, and medieval documents, such as accounting records for livestock and agricultural treatises, refer to it as “pockes” or “variola.” Many of these documents show severe declines in agricultural production when it surged. Every time the virus reemerged after a long hiatus, it was seen as something unknown.Early epidemics of sheeppox are thought to have occurred in the Eastern European and Caucasian steppe regions. Pastoralists in the steppes made clothing from wool, like the felted garments found on a Scythian mummy from the Altai region, and they relied on sheep for meat, dairy, fat, and skins in the often harsh environment. Some of the larger settlements in the steppe were trading hubs for metals and ceramics. Infected animals or products from them would come into contact with these items, and after foreign traders returned, sheeppox would break out in their home regions. Herds that encountered each other through seasonal moves were also at risk. When L’Hôte sampled medieval manuscripts, he found more virus DNA on the flesh side of the skin than the outside. It’s possible that the disease emerged with domestication.“Our findings provide a molecular understanding of SPPV in pre-Modern times,” the researchers said. “Although present in the Bronze Age, we find a particularly high number of SPPV genomes in the medieval period, associated with animal skin-based documents, implying that infection of sheep was a frequent challenge to European societies of this time.”Watch Our Science VideosElizabeth Rayne is a creature who writes. Her work has appeared in Popular Mechanics, Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.