Medieval Manuscripts Reveal 3,500 Years of Sheeppox Virus Evolution

Scientists have successfully extracted and sequenced DNA from the sheeppox virus preserved in animal skins used for medieval manuscripts, providing a 3,500-year evolutionary timeline of this historically significant pathogen. Sheeppox is a highly contagious and frequently fatal viral disease that, while largely eradicated from much of European livestock in the 20th century, still causes regional outbreaks, such as one affecting Greek sheep flocks in the previous year. The research, published in the journal *Science Advances*, demonstrates that parchment can serve as a viable medium for preserving animal pathogen DNA, suggesting that archives and libraries globally may hold genetic traces of past animal disease outbreaks.

Co-author Louis L’Hôte, a graduate student at University College Dublin, stated that the recording of ancient pathogen DNA has fundamentally altered the understanding of historical infectious diseases. He emphasized that the sheeppox virus genomes obtained from manuscripts offer insights into the pathogen's evolution and its impact on past societies, confirming its presence in Eurasian sheep herds for at least three and a half millennia. The earliest documented evidence of sheeppox infection dates back to the first century CE, with Roman accounts describing skin lesions, termed "pustules," in affected animals. More frequent mentions of deadly outbreaks, referred to as "pockes" or "variola" in sheep, appear in medieval agricultural texts and accounting documents from France, Spain, and England.

The study indicates a decrease in sheeppox outbreaks in 17th-century France, followed by a resurgence with high mortality rates in the 18th and 19th centuries. Great Britain did not experience a significant resurgence of the disease until 1847. This extensive historical record, derived from the biological material of manuscripts, allows researchers to trace the virus's genetic changes and its epidemiological patterns over centuries. The findings highlight the potential of historical documents not only as cultural artifacts but also as invaluable biological archives for understanding the long-term history of infectious diseases and their co-evolution with host populations. The methodology employed could be applied to other animal pathogens preserved in similar historical materials, expanding the scope of paleovirology and historical epidemiology.