Ancient viral DNA from the Viking Age brings scientists closer to the origin of smallpox
(ORDO NEWS) — While scientists are trying to figure out exactly where the coronavirus pandemic originated, other virologists are still looking for the causes of another deadly disease – smallpox.
Scientists have now discovered viral DNA from an ancient strain of smallpox in Viking Age archaeological remains from northern Europe.
Specimens dated no earlier than AD 603 provide compelling genetic evidence that smallpox originated about 1000 years earlier than it was first mentioned in historical records.
Several features of the ancient virus also suggest that it was widespread well before the 20th century, causing up to 500 million deaths.
Caused by the variola virus, smallpox remains the first and only disease that doctors have been able to eradicate from humans through vaccination – this victory was finally announced in 1980.
The spread of smallpox can be traced back to history. It struck the Moors when they invaded Spain and Portugal in the 8th century and then spread to Europe during the Crusades.
She also raged in the Egyptian and Hittite empires. A smallpox-like rash found on the ancient Egyptian mummy of Ramses V, who died in 1157 BC, suggests that smallpox existed about 3,000 years ago.
These observations are far from conclusive, unlike actual viral DNA, other historical records describing early infections like smallpox may be ambiguous.
According to current ideas, smallpox originated several thousand years ago in rodents somewhere in Africa, before it spread to humans, although scientists are still not completely sure about this.
Knowing how ancient smallpox viruses and modern strains are related can also help researchers understand how smallpox evolved into a deadly disease. In any case, this means the need to obtain more ancient samples of viral DNA.
Before the latest discovery, the earliest DNA evidence that virologists received was from a 17th century Lithuanian mummy (discovered by accident) and two specimens from the 19th and 20th centuries held in the Czech National Museum. Comparing the DNA in these samples to those of the modern smallpox virus dates their last common ancestor between 1530 and 1654 CE.
Virologist Barbara Muehleman of the Center for the Evolution of Pathogens at the University of Cambridge and colleagues searched for traces of ancient smallpox in the archaeological remains of nearly 1,870 people who lived in Eurasia and America.
“Ancient viruses, from archaeological remains, provide direct molecular evidence of past infections and can reconcile the inconsistency between historical records of possible infections and the oldest available genetic sequences,” the scientists explained in their article.
Their approach has recovered fragments of ancient viral DNA associated with modern smallpox from the bones and teeth of 26 long-dead people from northern Europe. Thirteen people had enough viral DNA material for deeper sequencing, and eleven of them were dated to the Viking Age, between 603 and 1050 A.D.
From these 11 samples, the team reconstructed nearly complete viral genomes, representing at least 96 percent of the complete virus sequence.
This result also confirms the prevailing theory that smallpox first appeared in rodents – ancient viral samples were closely related to the taterapox virus, another virus of the same poxvirus family that infects gerbils.
The now extinct ancient virus was widespread throughout northern Europe, but its seriousness cannot be said from DNA alone. “We cannot be sure that people have died as a result of infection,” the authors noted.
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