During the Middle Ages, documents were commonly inscribed on parchment, a writing material produced from the skins of sheep, goats, and cattle.
Researchers have discovered evidence in renowned medieval manuscripts that sheds light on the historical evolution of the deadly sheep pox virus—a highly contagious viral disease causing fever, skin lesions, and mortality in sheep. Such biological traces offer valuable insights into pathogen evolution and their impact on past societies.
An international consortium of geneticists, historians, virologists, protein chemists, and conservators, spearheaded by University College Dublin researchers, successfully extracted DNA from the animal skins used to create these ancient documents.
“The ability to identify ancient pathogen DNA has revolutionized our understanding of historical infectious diseases. This study demonstrates that parchment also preserves animal pathogen DNA,” explained Louis L’Hôte, lead author of the research.
The analysis included the 1,000-year-old York Gospels, a prime example of late Anglo-Saxon illuminated manuscripts, as well as earlier works like the Corpus Glossary from Corpus Christi College, Cambridge—one of the earliest English lexicons. Additional medieval texts from across Britain and continental Europe were also examined.
“Archives and libraries worldwide likely contain genetic traces of historical animal disease outbreaks,” noted the research team.
Sheep pox is a highly contagious disease rapidly spreading through flocks, resulting in substantial economic losses due to reduced milk production, inferior hide and wool quality, and trade restrictions. Importantly, this disease does not infect humans.
Published in Science Advances, the study revealed that specific manuscripts contained traces of the sheep pox virus DNA across multiple pages, implying that infected animals were used for parchment production. By combining DNA from these manuscripts with ancient sheep teeth from the Bronze Age, researchers determined the disease has plagued livestock for over 3,700 years.
“Ancient genomic data aids in understanding the evolution of contemporary pathogens. Unlike smallpox, the sheep pox virus genome remained remarkably stable over millennia,” added L’Hôte.
This stability suggests that early genetic mutations were critical to the virus’s adaptation to its host, offering potential strategies to combat future outbreaks.
