Thanks to vaccination efforts, smallpox — killer of hundreds of millions people around the world over the course of the 20th century alone — was eradicated in 1979. But even today the lethal variola virus, which causes the disease, is not completely impossible to come by.
A team of French and Russian researchers recently found new snippets of smallpox DNA in 300-year-old mummies from Siberia, according to an article in the New England Journal of Medicine released Wednesday.
While in northeastern Siberia in 2004, researchers discovered several burial sites, each containing frozen wooden graves buried in the permafrost. It seemed that most of the burials were individual and involved only one body, but one grave contained five frozen mummies — two children and three adults — which appeared to have been buried shortly after death.
Tissue samples from the lungs of mummy 2, a female adult determined to be less than 23 years old, had “iron inclusions” typical of blood from a hemorrhagic episode, the team reported. That evidence suggested that she had suffered a “sudden and lethal infection,” perhaps from smallpox.
They confirmed their theory through DNA sequencing, which revealed the presence of short fragments of variola genome. Genetic analysis also showed that only snippets of DNA from the new strain, called PoxSib, remained and that no intact viral particles had survived.
Before PoxSib, the oldest samples of DNA from variola had been obtained from patients 50-60 years ago, the study said.
“This genetic information could provide clues to past epidemics,” the team wrote, though they were unable to determine with complete precision where PoxSib fit on the smallpox family tree.
According to the research report, the virus “could be a direct progenitor of modern viral strains or a member of an ancient lineage that did not cause outbreaks in the 20th century.” The authors suggested that PoxSib might have been linked to a 1714 epidemic and could have been carried into Siberia “during Russian conquest.”
The new finding isn’t the first study of mummies to offer insight into disease. As Los Angeles Times reporter Thomas H. Maugh II reported in 2009, archaeologists found that ancient Egyptian mummies, some as much as 3,500 years old, had hardened artieries — suggesting that disease can stem from causes other than the modern lifestyle. A genetic analysis of King Tut’s remains showed that the young pharaoh suffered from malaria.
Here, the PBS show "Secrets of the Pharoahs" provides more information about extracting and studying DNA from mummies.
Read the scientists’ brief report in the New England Journal of Medicine, “Variola Virus in a 300-Year-Old Siberian Mummy.”