A landmark study has revealed the deep history of sheeppox, a highly contagious viral disease that threatens sheep populations and rural economies worldwide.
By analyzing ancient DNA from archaeological remains and historical artifacts, including medieval manuscripts, researchers led by University College Dublin and international collaborators including The Pirbright Institute traced the virus back at least 5,000 years, making it one of the oldest known viral livestock pathogens.
Sheeppox virus (SPPV) can decimate flocks, with mortality rates reaching up to 50% in adults and nearly 100% in young animals. Infected sheep suffer fever, loss of appetite, eye discharge, and distinctive skin lesions, often leading to losses in meat, milk, and wool production. The disease is classified as notifiable by the World Organisation for Animal Health.
In the largest study of its kind, scientists led by University College Dublin (UCD) screened more than 750 samples from across Eurasia, spanning 14,000 years of history, and reconstructed 22 ancient viral genomes. They identified 39 ancient cases of sheeppox, including well-preserved viral genomes recovered from Bronze Age sheep remains in central Asia.
The findings confirm sheeppox was already infecting domesticated sheep herds nearly four thousand years ago when pastoralist societies relied on livestock for survival.
In a surprising discovery, the research team detected sheeppox DNA in medieval manuscripts made from animal skins. Documents from the UK, France, and central Europe contained traces of the virus, suggesting infected animals were commonly used in parchment production.
Photo credit: Cambridge, Trinity College, MS B.10.5, fol. 62v, the Epistles of St Paul, Ireland/Northumbria, 700–800 CE.
Reproduced with kind permission of the Master and Fellows of Trinity College Cambridge.
Some manuscripts date back to the 8th century, indicating sheeppox was widespread in medieval Europe. The findings raise the prospect that other historical artifacts may preserve genetic evidence of ancient diseases.
Dr Kevin Daly, Assistant Professor at UCD’s School of Agriculture and Food Science, said:
“The findings open new avenues for collaborative research with Pirbright, including the potential recovery of ancient genomes from related viruses such as goatpox and lumpy skin disease, which could further clarify the evolutionary history of this important group of pathogens.”
Pirbright’s Head of Genomics, Dr Tim Downing, and Dr Jonas Albarnaz, a specialist in capripoxvirus biology at the Institute, contributed to the study. Dr Downing said:
“By leveraging the expertise gained through our investigations into capripoxvirus biology and genomics, we were able to help understanding the complex phylogenetic relationships of the ancient sheeppox genomes with modern capripoxviruses.”
Dr Albarnaz added: “This study is a major advance towards uncovering the mechanisms of coevolution of capripoxviruses with livestock hosts over millennia, informing about viral pathogenesis, and development of control strategies.”
By reconstructing 22 ancient viral genomes, researchers were able to map the evolution of sheeppox over thousands of years. Their analysis suggests that the virus diverged from related livestock viruses around 5,000 years ago, likely following the domestication of sheep.
The study also identified a now-extinct medieval European lineage of the virus, distinct from modern strains, which appears to have circulated widely during the Middle Ages.
The presence of sheeppox in early pastoralist communities is likely to have had a profound impact on food supply, textile production and trade. The disease may also have spread along ancient trade and migration routes. By tracking how pathogens adapt over millennia, scientists say they can better understand current disease dynamics and future risks.
The research was funded by Taighde Éireann - Research Ireland and the European Research Council (ERC).
Read the Paper: 3,500 years of sheeppox virus evolution inferred from archaeological and codicological genomes.