Scientists have recovered sheeppox virus DNA from the animal skins used to make the parchment of medieval manuscripts, reconstructing roughly 3,500 years of evolution of a disease that once devastated European flocks. The study, published in Science Advances, suggests libraries and archives worldwide may hold genetic traces of past livestock outbreaks hidden in their oldest books.
Sheeppox is highly contagious and often fatal; it largely disappeared from European livestock in the 20th century, though regional outbreaks still occur, including one in Greece last year. Because pathogens do not fossilize, little was known about the virus's genetic history. But parchment made from animal skin — often sheep leather — can preserve DNA for centuries.
A team led by University College Dublin researchers sampled manuscripts held at Yale, Cambridge, Corpus Christi College, the Lambeth Palace Library and Trinity College, including the Trinity Gospels, the Lambeth Bible and the roughly 1,000-year-old York Gospels. Multiple pages carried pathogen DNA, showing infected animals were used for the parchment. Surprised, the researchers also found the virus on calfskin and goatskin parchment, hinting at cross-species infection or contamination. Bronze Age sheep teeth from Russia and Central Kazakhstan let the team push deeper: sheeppox diverged from goatpox and lumpy skin disease viruses between 11,500 and 3,700 years ago, roughly coinciding with animal domestication in Europe. In all, 21 ancient genomes were recovered, spanning 1700 BCE to early modern Europe.
"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 co-author Kevin G. Daly. Colleague Louis L'Hôte added: "It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past."
