- Smallpox was a viral infection that caused disfiguring sores and even death
- It is believed to have come from rodents but its history and origins are a mystery
- Experts hunted for traces of smallpox in archaeological sites across Europe
- They found evidence of the disease in teeth from various 7th Century burial sites
- The findings indicate that smallpox was prevalent across Europe at that time
- However, analysis revealed that the strains were different from the modern one
Viking raiders were responsible for spreading the deadly smallpox to Britain and around the globe, genetic information extracted from ancient teeth has revealed.
The teeth samples contained extinct strains of smallpox — different to the modern virus that was declared eradicated in 1980 — that dated back to the 7th Century.
The findings indicate that smallpox was widespread in northern Europe during that period — pushing back the disease's first known case by some 1,000 years.
Smallpox is a viral infection that causes a fever, vomiting, headaches and a rash which turns into disfiguring sores and pustules that could leave permanent scars.
In around 30 per cent of cases, smallpox infection proved fatal.
The international research team said that it is unclear if the ancient smallpox strains were as deadly — but that the Vikings likely helped the spread of the disease.
Knowing more about the evolutionary history of viruses such as smallpox, they added, may help in the battle against new and emerging infectious diseases.
'Knowledge from the past can protect us in the present,' said paper author and computational biologist Terry Jones of the University of Cambridge.
'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 — a disease which can be transmitted to humans from animals,' he explained.Caused by the variola virus, smallpox was one of the most hostile human diseases, killing more than 300 million people in the 20th century alone.
This virus became the first human disease to be eradicated — with the last natural case reported in Somalia in 1977 — following an extensive global vaccination effort.
However, concerns remain that the virus could re-emergence, with the possibility of another strain spilling over from animals at any moment.
Scientists say that the exact origin and evolution of smallpox in humans remains a mystery — however, some virologists believe that the variola virus may have been first transmitted to humans from rodents thousands of years ago.
To find out more, Dr Jones and colleagues searched for evidence of ancient smallpox at various archaeological sites.
The team found extinct strains of the variola virus in the skeletons of humans at 11 different burial sites — located in Denmark, Norway, Russia and the UK — and all from the Viking era.
More evidence of these viral strains was found in human remains from Öland, an island that lies off of the southeast coast of Sweden.
Analysis revealed that the genetic structures of the ancient smallpox strains were 'remarkably' different from their modern counterpart — suggesting the virus evolved, the researchers said.