Some Vikings may have died from now-extinct strains of one of humankind’s deadliest pathogens: smallpox.
Researchers collected DNA from viruses in the remains of northern Europeans living during the Viking Age, some of whom were likely Vikings themselves, and found that they were infected with extinct but related versions of the variola virus that causes smallpox, the team reports in the July 24 Science. The new finding pushes back the proven record of smallpox infecting people by almost 1,000 years, to the year 603.
Researchers had previously discovered ancient traces of variola virus DNA in a mummy from the mid-1600s, which put the common origin of modern strains in the 16th or 17th century (SN: 12/8/16).
It is still uncertain when the virus that causes smallpox first began to infect people. The disease is estimated to have killed as many as 500 million people and is the only human pathogen to have been eradicated globally.
Written records from more than 3,000 years ago have documented smallpox-like symptoms, and scientists have identified possible smallpox skin lesions on mummified remains. But it’s difficult to prove that the smallpox virus was the cause.
“This is really exciting work,” says Ana Duggan, an evolutionary geneticist at McMaster University in Hamilton, Canada, who was not involved in the study. “Our understanding of this historical and devastating disease just got a lot wider. We are uncovering [variola virus] diversity that was unknown and unappreciated until right now.”
Martin Sikora, a computational biologist at the University of Copenhagen, and his colleagues isolated viral DNA from the teeth and bones of 1,867 humans who lived approximately 31,000 to 150 years ago. Of those people, 13 had remnants from the variola virus. Eleven remains belonged to people — including some thought to be Vikings — who had lived in northern Europe, western Russia and the United Kingdom during the Viking Age more than 1,000 years ago. Two others lived in western Russia during the 19th century and were infected with variola virus strains closely related to modern versions.
The team reconstructed nearly complete genetic blueprints of four of the 11 ancient viruses, which reveal that the Viking-era strains belong to a now-extinct group of variola viruses. During that period, smallpox may have been widespread throughout Europe and could have caused serious disease, Sikora says. It’s also possible that if Vikings were infected, they may have spread the disease as they traveled.
Though the ancient variola viruses are now gone, remnants of their DNA help uncover humans’ extensive relationships with pathogens. “These kinds of pandemics have been part of our history,” Sikora says. “What we see today is only the tip of the iceberg of what was around.”