December 9, 2016
Mummified smallpox virus shows the disease isn’t as old as we thought
The mummy of a young boy discovered buried in a crypt beneath a Lithuanian church contains the oldest-known complete set of smallpox genes, and scientists hope that the discovery will shed new light on the history of the infamous pathogen, according to NPR and BBC News reports.
Save for a few secured, frozen samples, smallpox was eradicated following a global vaccination campaign during the 1970s, but to this day, little is known about the origins of the disease. Now, a team of scientists from Ontario’s McMaster University discovered DNA from the smallpox virus-- the Variola virus, in a skin sample obtained from the 17th-century remains.
As evolutionary geneticist Hendrik Poinar, senior author of a new paper published Thursday in the journal Current Biology, said in a statement, “Scientists don’t yet fully comprehend where smallpox came from and when it jumped into humans. This research raises some interesting possibilities about our perception and the age of the disease.”
Experts had long thought that smallpox had been around for thousands of years, affecting those living in ancient China, India and Egypt – including pharaoh Ramses V, who according to some accounts suffered from the disease before his death in 1145 BC. By sequencing the DNA of this newfound sample, they found that the disease has likely only been around for hundreds of years.
Condition appears to be far younger than previously thought
The newly obtained Variola virus samples are the oldest human virus ever to be sequenced, Dr. Edward Holmes of the University of Sydney told BBC News. Radiocarbon dating showed that the boy lived sometime around 1650 AD (a period when smallpox was common across Europe) but the evolutionary history of the disease itself led to a surprising discovery.
“This fossil tells us that the virus' evolutionary history is much more recent than we thought- it's actually only hundreds of years rather than thousands of years,” Dr. Holmes explained. But he added that it was not possible to determine exactly where the disease came from, when it may have first appeared in humans, and what its ancestor might have been.
Interestingly, the researchers told NPR that the mummified child showed no signs of the disease, including pockmarks. Study co-author Henrik Poinar told the media outlet that the disease seems to be “human specific,” unlike other pox viruses, which tend to affect other animals. If smallpox did begin in a different creature before affecting humans, scientists have no clue which creatures it might have originally affected, which Poinar said he finds “fascinating.”
The study authors compared the new Variola virus samples, which are not alive and which pose no threat of transmission, to strains contained in a modern databank dating back to 1940. Based on that comparison, they were able to determine that the evolution of the virus is far more recent than previously believed, and that all available smallpox strains originated from an ancestor dating no further back than 1580, the researchers said in a statement.
This discovery “raises important questions about how a pathogen diversifies in the face of vaccination,” noted Ana Duggan, a post doctoral fellow in the McMaster Ancient DNA Centre and one of the researchers involved in the new study. “While smallpox was eradicated in human populations, we can’t become lazy or apathetic about its evolution – and possible reemergence – until we fully understand its origins.”
Image credit: Kiril Cachovski/Lithuanian Mummy Project