Scientists have extracted and sequenced sheeppox virus DNA from medieval manuscripts, providing a 3,500-year history of the disease. The research, led by Louis L’Hôte, a graduate student at University College Dublin, utilized parchment made from sheepskin to trace the evolution of the virus and its impact on Eurasian sheep herds.
Sheeppox, a contagious and often fatal disease for sheep, was largely eradicated in much of Europe by the 20th century, though regional outbreaks still occur, such as one in Greece last year. The earliest written evidence of sheeppox dates back to the first century CE, with Roman accounts describing skin lesions in sheep. By the Middle Ages, outbreaks were frequently documented in agricultural texts and accounting records from France, Spain, and England, referred to as “pockes” or “variola.”
While outbreaks declined in 17th-century France, they resurged in the 18th and 19th centuries, often causing high mortality rates. Great Britain did not experience a resurgence until 1847. Prior to this study, the genetic history of the sheeppox virus remained largely unknown. Researchers turned to analyzing DNA within medieval manuscripts, as the parchment was commonly made from sheep leather.
“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. It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past,” said L’Hôte. “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.” The findings were published in the journal *Science Advances*.
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