Medieval manuscripts reveal 3,500-year evolutionary history of sheeppox virus

An international research team has discovered DNA from the sheeppox virus (SPPV) preserved within the parchment of medieval manuscripts. The findings, led by University College Dublin (UCD), demonstrate that ancient texts can serve as biological archives for the diseases that plagued early European livestock.

Using manuscripts such as the York Gospels and the Corpus Glossary, the team detected SPPV DNA in documents dating from the 8th to the 14th century. These samples originated from Britain, France, Austria, and the Upper Rhine region. By integrating this data with genetic material from Bronze Age sheep teeth found in Russia (c. 1336–1130 BC) and Kazakhstan (c. 1875–1645 BC), the researchers reconstructed a 3,500-year evolutionary history of the virus. The study, published in Science Advances, highlights how the animal skins used to create parchment preserve the biological state of the livestock at the time of death.

The biological archive

While European treatises from the 13th to 16th centuries contain written records of "pockes" or "variola" in sheep, this genetic evidence pushes the known presence of the disease in Europe back to at least the 8th century. Parchment, made from the skins of sheep, goats, and cattle, effectively traps genetic traces of pathogens.

"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," said Louis L’Hôte, a PhD candidate at UCD and the study's lead author. Associate Professor Kevin G. Daly of UCD added that the project proves parchments preserve not only cultural history but also the "landscape of disease" in medieval livestock.

Implications for modern science

The discovery suggests that global libraries and archives may hold vast, untapped genetic records of past animal disease outbreaks. Beyond historical curiosity, the study provides critical genomic insights. Researchers found that the sheeppox genome has remained remarkably stable over millennia, a stark contrast to the rapid evolution seen in the smallpox virus.

This stability offers a window into how the pathogen evolved to infect its hosts. Understanding these evolutionary patterns may provide essential data for scientists currently fighting active sheeppox outbreaks, such as those causing significant economic damage in Greece today.

Future directions

The research opens the door for wider screening of archival materials to map the spread of ancient zoonotic diseases. While the core evolutionary timeline is now established, researchers continue to investigate the specifics of how these pathogens persisted across different regions of Europe and Asia. The study confirms that the physical medium of the written word can provide biological answers that the text itself does not contain.