Sheeppox, a highly contagious and often fatal viral disease, was largely eradicated from European livestock in the 20th century, although regional outbreaks still occur, such as one that afflicted flocks in Greece last year. To trace the virus's evolution over roughly 3,500 years, researchers turned to an unconventional source: the parchment pages of medieval manuscripts.
“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 co-author Louis L’Hôte, a graduate student at University College Dublin, in a statement. “It is possible that archives and libraries around the world also contain the genetic traces of disease outbreaks in animals in the past.”
L’Hôte added that 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 earliest written evidence of sheeppox infection dates to the first century CE, with Roman accounts describing outbreaks of skin lesions, known as pustules, in sheep. By the Middle Ages, deadly outbreaks of “pockes” or “variola” in sheep were frequently recorded in agricultural texts and accounting documents in France, Spain, and England. Outbreaks appeared to decline in 17th-century France before re-emerging with high mortality in the 18th and 19th centuries; Great Britain did not see a resurgence until 1847.