By
Stuart Black / Alamy
–
DNA from ancient smallpox viruses was found in the bones and teeth of a dozen people who lived in northern Europe during the Age of the Vikings. Unexpectedly, these strains of smallpox are quite different from the strain that was wiped out in the 20th century – and possibly much less deadly.
Historical accounts and lesions found on Egyptian mummies suggest that the Smallpox virus, which causes smallpox, has been rampant for thousands of years. Barbara Mühlemann of the University of Cambridge and her colleagues now have the first unambiguous evidence.
They began by looking for viral sequences in the previously sequenced DNA of nearly 2,000 individuals who lived in Eurasia and the Americas between 30,000 and 150 years ago. “Presumably many people have died from the virus,” she says.
Publicity
In these people, viral DNA may be present in their remains and may have been sequenced with their own DNA. Indeed, the team found signs of Smallpox DNA in 26 individuals.
They then looked for more viral DNA in the original samples. They found it in 13 individuals, 11 of whom died between 600 and 1050 AD – straddling the Viking Age of 793 to 1066 AD.
Most of these people died in Scandinavia or in what is now Western Russia. Three were found on an island in the Baltic Sea called Öland, one in a ship burial around AD 700 and two more in separate burials around AD 1,000. The latter two probably died in the same outbreak.
the Smallpox The virus was also found in a man in a mass grave in Oxford, UK, which is strange given that all 35 men at that grave were brutally killed. These are believed to be Viking warriors killed in 1002 AD after Ethelred the Unready ordered the deaths of all Danes in England – the St. Brice Massacre.
In four cases, Mühlemann recovered nearly complete viral genomes. What they reveal was unexpected.
The ancestor of Smallpox The virus probably had around 200 genes, similar to some smallpox viruses still circulating in animals. The strain eliminated by vaccination in the 20th century – which killed 1 in 3 people – had lost around thirty genes.
The strains sequenced by Mühlemann had lost only half of these 30 genes. They derive from the same ancestor as the 20th century virus, but did not spawn it. Instead, they’re a now extinct side branch.
“It’s more complicated than anyone imagined,” says Terry Jones, also a fellow of the University of Cambridge.
Strains with the full set of 200 genes usually only cause mild illness, says Antonio Alcamí of the Autonomous University of Madrid, Spain, who was not on the team. He believes the Viking Age type of virus was less deadly than the 20th century type. “He was probably capable of killing but it wasn’t that bad,” he said.
This flies in the face of conventional thinking, that viruses are the most deadly when they first spread to humans and evolve to become less deadly, as viruses that cause serious illness are less likely to spread. spread.
“Why he has become more virulent does not make sense,” says Alcamí.
The team themselves aren’t making any claims one way or another, as they aren’t immunologists like Alcamí. “We think we cannot say for sure that this virus was less virulent in the past,” says Mühlemann.
One explanation for this diversity of strains is that the smallpox virus has passed from animals to humans more than once. It could mean it’s more likely to happen again than we thought, Jones says.
More and more people are becoming infected with monkeypox viruses – the normal host of which is unknown despite the name – but so far there has been no sustained human-to-human spread. The increase in cases could be due to the fact that people are no longer vaccinated against smallpox after its eradication, says Mühlemann.
Journal reference: Science, DOI: https://doi.org/10.1126/science.aaw8977
Learn more about these topics:
–
