Sheeppox, a deadly virus that has plagued sheep for thousands of years, has revealed its genetic history through medieval manuscripts. Scientists extracted and sequenced sheeppox DNA from animal skins used for parchment, providing insights into the evolution of this virus over the last 3,500 years. This pioneering research, published in Science Advances, suggests that archives and libraries worldwide might hold the genetic traces of past animal diseases.

The earliest written evidence of sheeppox infection dates back to the first century CE, with Roman accounts describing outbreaks of skin lesions. By the Middle Ages, more frequent mentions of ‘pockes’ or ‘variola’ in sheep appear in agricultural texts and accounting documents from France, Spain, and England. Despite a decline in outbreaks in 17th-century France, they resurged in the 18th and 19th centuries, often with high mortality rates. Britain experienced a resurgence in 1847, further highlighting the virus’s enduring presence.

According to co-author Louis L’Hôte, a graduate student at University College Dublin, 'These genomes help us understand how these pathogens evolved and how they impacted past societies—such as sheeppox virus, which we show has been affecting Eurasian sheep herds for at least three and a half millennia.' This breakthrough not only aids in understanding historical diseases but also underscores the potential of medieval manuscripts as invaluable sources for genetic research.

The study’s findings have implications beyond just sheeppox. They suggest that archives and libraries worldwide might contain the genetic traces of past animal diseases, offering a unique perspective on the history of infectious diseases. This could revolutionize the way we study and understand the evolution of pathogens, providing a new layer of insight into the biological and historical records of the past.