An international team of scientists has discovered for the first time that Vikings had smallpox 1,400 years ago. The experts have now genetically sequenced previously unknown strains of the virus that were found in the teeth of Viking skeletons from sites across northern Europe.
The findings suggest that Vikings helped to drive the worldwide spread of the virus, which was the deadliest in history. During the 20th century alone, an estimated 300 million people died of smallpox, before it became the only human infectious disease ever to be completely eradicated in 1980.
Study lead author Eske Willerslev is a professor in the Department of Zoology at St John’s College, University of Cambridge.
“We discovered new strains of smallpox in the teeth of Viking skeletons and found their genetic structure is different to the modern smallpox virus eradicated in the 20th century,” said Professor Willerslev.
“We already knew Vikings were moving around Europe and beyond, and we now know they had smallpox. People traveling around the world quickly spread Covid-19 and it is likely Vikings spread smallpox. Just back then, they traveled by ship rather than by plane.”
“The 1,400-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.”
Historical documents suggest that smallpox may date back to as far as 10,000 BC., but the current study has produced the first scientific proof that the virus was present before the 17th century.
While it is not known how it first infected humans, the smallpox virus is believed to have originated in animals just like COVID-19. When a pathogen jumps from an animal to a human, the resulting disease is referred to as a zoonotic disease.
The deadly disease, which spread through airborne respiratory droplets, killed about one-third of those infected and left just as many permanently scarred or blind.
“The timeline of the emergence of smallpox has always been unclear but by sequencing the earliest-known strain of the killer virus, we have proved for the first time that smallpox existed during the Viking Age,” said study senior author Professor Martin Sikora from the Centre for GeoGenetics, University of Copenhagen.
“While we don’t know for sure if these strains of smallpox were fatal and caused the death of the Vikings we sampled, they certainly died with smallpox in their bloodstream for us to be able to detect it up to 1,400 years later. It is also highly probable there were epidemics earlier than our findings that scientists have yet to discover DNA evidence of.”
The researchers found traces of smallpox across 11 Viking-era burial sites in Denmark, Norway, Russia, and the UK. They also discovered smallpox in multiple human remains from Öland, an island off the east coast of Sweden with a long history of trade.
Using four of the samples collected from these sites, the team reconstructed near-complete variola virus genomes.
Study first author Dr. Lasse Vinner is a virologist from The Lundbeck Foundation GeoGenetics Centre.
“Understanding the genetic structure of this virus will potentially help virologists understand the evolution of this and other viruses and add to the bank of knowledge that helps scientists fight emerging viral diseases,’ said Dr. Conner.
“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. We don’t know how the disease manifested itself in the Viking Age – it may have been different from those of the virulent modern strain which killed and disfigured hundreds of millions.”
Study senior author Dr. Terry Jones is a computational biologist at the Centre for Pathogen Evolution at the University of Cambridge.
“There are many mysteries around poxviruses. To find smallpox so genetically different in Vikings is truly remarkable. No one expected that these smallpox strains existed. It has long been believed that smallpox was in Western and Southern Europe regularly by 600 AD, around the beginning of our samples,” said Dr. Jones.
“We have proven that smallpox was also widespread in Northern Europe. Returning crusaders or other later events have been thought to have first brought smallpox to Europe, but such theories cannot be correct. While written accounts of disease are often ambiguous, our findings push the date of the confirmed existence of smallpox back by a thousand years.”
Dr Jones added that knowledge from the past can protect us in the present. “When an animal or plant goes extinct, it isn’t coming back. But mutations can re-occur or revert and viruses can mutate or spill over from the animal reservoir so there will always be another zoonosis.”
“Smallpox was eradicated but another strain could spill over from the animal reservoir tomorrow,” said Professor Willerslev. “What we know in 2020 about viruses and pathogens that affect humans today, is just a small snapshot of what has plagued humans historically.”
The study is published in the journal Science.
By Chrissy Sexton, Earth.com Staff Writer