DNA analysis reveals that a different version of the disease existed a thousand years earlier than previously thought in Northern Europe.
Genetic analysis of teeth from different Viking skeletons discovered in northern Europe revealed the presence of extinct strains of the smallpox virus.
The study, published this week in the journal Science, proves for the first time that the disease existed 1400 years ago – a thousand years earlier than previously thought.
Smallpox spreads from person to person through infectious droplets. It is highly lethal: in the 20th century alone, it killed approximately 300 million people. The eradication of the disease did not happen until 1980, thanks to a global mass vaccination effort.
“We already knew Vikings were moving around Europe and beyond, and we now know they had smallpox. People travelling around the world quickly spread Covid-19 and it is likely Vikings spread smallpox,” explained Eske Willerslev, who led the research. “Just back then, they travelled by ship rather than by plane. The 1400-year-old genetic information extracted from these skeletons is hugely significant because it teaches us about the evolutionary history of the variola virus that caused smallpox.”
Historians believe that smallpox has existed since 10,000 BC, but until now there was no scientific evidence that the virus was present before the 17th century.
It is not known how it first infected humans, but it is likely to be a zoonosis, a pathogen that jumped from another species to a human host.
“The early version of smallpox was genetically closer in the pox family tree to animal poxviruses such as camelpox and taterapox, from gerbils. It does not exactly resemble modern smallpox which show that virus evolved,” said Lasse Vinner, co-author of the study.
According to Terry Jones, one of the senior authors of the study, finding strains of smallpox genetically different in Vikings was a surprise, because until then it was thought that the disease occurred regularly in Western and Southern Europe at that time. “We have proved that smallpox was also widespread in Northern Europe,” Jones said.