Variola virus DNA found in bones of people from Denmark to Russia around Viking era
The Vikings are known for their intrepid seafaring, fearsome fighting and extensive trading, but it seems it may not only have been goods and weapons they carried on their travels – they could also have carried a deadly disease.
Researchers say they have found the world’s earliest confirmed case of smallpox, revealing the disease was widespread across northern Europe during the Viking age.
“I think it is fair to assume the Vikings have been the superspreaders,” said Eske Willerslev, professor of ecology and evolution at the University of Cambridge and director of the Lundbeck Foundation GeoGenetics Centre at the University of Copenhagen, who led the research.
Smallpox, a deadly infectious disease with symptoms including pus-filled blisters, is caused by the variola virus. Once described by the 18th-century English physician Edward Jenner as the “most dreadful scourge of the human species”, in the 20th century alone the disease is thought to have killed between 300 million and 500 million people.
A global vaccination programme led to the World Health Organization declaring the disease eradicated in 1980: the virus is now stored in just two laboratories in the world.
But despite its heavy mark on human history, the origins of smallpox have remained murky.
The ancestor of the variola virus is thought to have crossed from rodents to humans thousands of years ago in Africa. Indeed written accounts and mummified remains, including those of Ramses V, suggest smallpox may have been present in ancient Egypt. Before the new research, however, the earliest case of smallpox confirmed by genetic data was that of a 17th century child found mummified in Lithuania.
Writing in the journal Science, Willerslev and colleagues report how, as part of a wider project studying the remains of 1,867 humans, they found variola virus DNA in the teeth or bones of 11 men and women from Denmark to Russia, dating from about AD600 to AD1050 – a period that overlaps with the Viking age.
“It is the oldest confirmed case of smallpox,” Willerslev said.
While the researchers note the 11 individuals were likely infected with the variola virus when they died, it is unclear if it killed them. Indeed one individual from Oxford seems to have had a particularly grisly death, having been stabbed from behind either as part of a widespread massacre of Danes or the killing of a group of Viking raiders.
The researchers extracted near-complete viral genomes from four of the individuals, with subsequent analysis revealing that this now-extinct Viking age variola virus differs from modern strains, likely evolving in parallel from a common ancestor that existed about 1,700 years ago.
The team say the findings chime with written accounts that smallpox was in western and southern Europe by the late sixth century, and debunks the idea the disease was introduced to England by the Normans or brought back to Europe by Crusaders.
While it is not clear how or when the modern forms of smallpox turned up in northern Europe, Willerslev said one possibility is that their ancestor was already present during the Viking age, but was simply less abundant than the newly discovered strain.
Crucially, said Willerslev, the findings shed light on the evolution of variola virus and could even provide clues on how other pox diseases in animals could mutate and potentially pose a risk to humans.
Hendrik Poinar, director of the Ancient DNA Centre at McMaster University, who was not involved in the work, described the research as exciting, but said how the Viking age variola virus manifested was likely to remain a mystery given researchers would not be allowed to carry out experiments.
However Sanjoy Bhattacharya, professor in the history of medicine and director of the World Health Organization’s Collaborating Centre for Global Health Histories at the University of York likened the findings to a “storm in a teacup”.
He said: “It is known from Egyptian mummies that smallpox existed in ancient times. We also know that trade links were widespread, and this carried disease around the world. So, why should smallpox amongst the Vikings be such a surprise?”