Virus DNA from a deadly disease found in thousand-year-old medieval manuscripts

Pages that preserve the trace of flocks

According to UCD, as relayed by ScienceDaily, several manuscripts of historical importance yielded DNA from sheeppox virus (SPPV). Among them are the York Gospels, considered one of the most beautiful illuminated manuscripts of the early Anglo-Saxon period, as well as the Corpus Glossary, held at Corpus Christi College, Cambridge, one of the oldest English dictionaries.

The researchers found the virus on several pages of certain documents, indicating that infected animals had supplied some of the skins used to make them.

Parchment, the biological memory of the animal

Before paper spread, manuscripts were written on carefully prepared skins from sheep, goats or cattle. These materials can retain traces of the animal's biological history, including infections present at the time of its death.

One finding surprised the team: viral DNA was found on parchments made from calf and goat skin. Since the virus mainly infects sheep, two hypotheses are proposed: other farm species may have been affected, or the viral material may have contaminated the skins during manufacture.

Bronze Age sheep teeth

To reach further back in time, the team analysed DNA extracted from sheep teeth dating to the Bronze Age. Teeth protect genetic material effectively for millennia, often better than other skeletal remains.

The oldest known genetic traces of the virus were identified in teeth from pastoral sites on the Eurasian steppe. Combined with the manuscript data, they show that the disease has affected flocks for more than 3,700 years.

A remarkably stable virus

By comparing ancient DNA with sequences of modern viruses, the researchers estimated that the main branches of the capripoxvirus family (sheeppox, goatpox and lumpy skin disease) diverged between 11,500 and 3,700 years ago. This period coincides with animal domestication and the major movements of sheep into Europe.

Notably, the sheeppox virus genome has changed very little over the millennia, unlike that of human smallpox. According to Louis L'Hôte, a doctoral student at UCD and first author, this stability suggests that earlier genetic changes played a key role in the virus's adaptation to its host.

A health issue still relevant today

Sheeppox remains a threat to livestock farming: an outbreak is currently under way in Greece, according to Louis L'Hôte, who stresses the significant economic losses it causes. It can kill many animals, especially young ones, and reduce production of wool, meat and milk.

For Kevin G. Daly, professor at UCD and supervisor of the study, libraries and archives may hold many other traces of past animal diseases. The team, drawing on more than thirty institutions, combines genetics, history, virology and conservation.