The discovery of smallpox virus in skeletal and dental remains from the Viking Age shows that the world’s deadliest infectious disease ever was already widespread 1,000 years earlier than previously thought.
Vikings were historical superspreaders of deadly viruses and bacteria, carrying them all over Europe.
One such disease was smallpox, and a new study pushes back the timeline for the world’s deadliest virus for humans by 1,000 years.
The researchers behind the study believe that the discovery has several perspectives, including that that the Vikings were superspreaders and that researchers have now obtained unique insight into the making of a microbial mass murderer.
However, the study also indicates the importance of knowing about the genetic development of viruses so that we can be prepared if smallpox once again ravages humanity and spreads death and destruction.
“Although smallpox has been eradicated in humans, it is still present in cows, monkeys and other animals. Similar to COVID-19, smallpox might one day be transmitted to humans again, and so knowing how smallpox evolved historically into a deadly disease is extremely important,” explains a researcher behind the study, Eske Willerslev, Professor and Director, Lundbeck Foundation GeoGenetics Centre, Globe Institute, University of Copenhagen.
The research has been published in Science.
Insight into how smallpox develops
The new study provides researchers with additional knowledge on how to combat the smallpox virus if it re-emerges one day in a new and dangerous version.
This is the assessment of Jan Pravsgaard Christensen, Professor at the Department of Immunology and Microbiology at the University of Copenhagen. He is not connected to the new study, but he has read it and thinks it is very interesting.
“Imagine that smallpox virus re-emerges at some point in the future. We may not recognize it as smallpox virus if we only compare it with the version of smallpox we eradicated in 1980. The new study provides insight into what the smallpox virus might also look like, and this can be used to quickly identify such viruses as being smallpox and also to find a way to combat the virus if the smallpox vaccine we used to eradicate the 1980 version turns out not to be effective against a new version,” he says.
The deadliest infectious disease ever
Smallpox has killed more people than any other infectious disease in history.
In the 20th century alone, between 300 and 500 million people died a painful death with blisters all over their bodies. The mortality rate was between 20% and 60%, and smallpox has killed more people than all epidemics of the plague combined.
The researchers screened genetic material from hundreds of Viking skeletal and dental remains that have been found throughout Europe for DNA from bacteria and viruses to determine the Vikings’ illnesses.
Thirteen of the Vikings were apparently infected with smallpox, which also indicates that the disease was surprisingly common. However, the new research results cannot say anything about how ill smallpox made people in the Viking Age.
“When we found DNA from smallpox in our samples, the virologists we work with froze because, in their world, smallpox represents the greatest fear of a global pandemic. They were decidedly panicked at the thought of having to work with this virus, although of course it was harmless and fragmented in our findings. Nevertheless, WHO also got involved in the project because today smallpox is only present in two places: in maximum-containment laboratories in the United States and Russia. This virus is not to be trifled with,” explains Eske Willerslev.
Perspectives in the new discovery
According to Eske Willerslev, the discovery has many perspectives.
The researchers found the world’s oldest smallpox. The oldest previous discovery dates back to the 17th century, and the 13 new discoveries are up to 1,000 years older.
“This shows that smallpox has existed in humans for much longer than we previously thought,” says Eske Willerslev.
Second, the smallpox virus the researchers discovered differs from the modern one. According to Eske Willerslev, this indicates that smallpox has made the zoonotic leap from being able to infect animals to being able to infect humans not just once but probably several times.
“The insight into this second strain of smallpox improves our understanding of what makes smallpox dangerous and contagious. Then we can start screening for these genetic traits in the smallpox viruses that we find in animals and try to predict when they will have the characteristics necessary to make this zoonotic leap again. If a virus has once taken this leap, it is only a matter of time before it does so again, and then we must be prepared so that it does not take us by surprise,” explains Eske Willerslev.
Catalogue of mutations that can make smallpox dangerous
Understanding the mutations in the smallpox virus in a historical perspective may also advance researchers’ knowledge about what would make the current smallpox virus vaccine ineffective.
Eske Willerslev belongs to the last generation that was vaccinated against smallpox, but it is not certain that this vaccine will protect against the disease if it reappears.
If smallpox leaps again from animals to humans, it may look completely different and sneak past the vaccine’s protective shield.
“This information cannot be obtained by solely studying smallpox from the 20th century. We can cause several mutations and determine whether smallpox virus can survive individual mutations, but this study provides a catalogue of the mutations that may lie in the virus’s DNA that can make it contagious and dangerous. From the Viking Age to the present, the smallpox virus has streamlined its genetic mechanism and has become better at infecting humans, and we can determine how it has done this,” says Eske Willerslev.
Unprotected Bronze Age sex?
The study also sheds light on the health of the Vikings.
Many people may have the impression that the Vikings were blonde, beautiful women and men with a strong physique and good health.
The study appears to refute this impression.
Instead, the Vikings spread many different diseases that have ravaged people, villages, towns and countries. There is a good reason why life expectancy was much shorter 1,000 years ago than it is today.
“They were infected with all sorts of stuff, and the idea of the pure Viking woman with long blonde hair is pure fantasy. Having unprotected Bronze Age sex with her was a really bad idea,” smiles Eske Willerslev.
“Diverse variola virus (smallpox) strains were widespread in northern Europe in the Viking Age” has been published in Science. The Danish National Research Foundation, Innovation Fund Denmark, Lundbeck Foundation, Novo Nordisk Foundation, Carlsberg Foundation and Villum Foundation funded the study.