Smallpox virus found in 300-year-old mummies

The variola virus, which causes smallpox, was recently found in the DNA of five 300-year-old mummies buried in northeastern Siberia.

Smallpox, a killer of millions in the 20th century alone and a potential bioweapon, was eradicated in 1979, but the find could provide clues about the disease's past progression, according to the New England Journal of Medicine.

In 2004, researchers discovered several graves frozen in permafrost. Most of the graves contained a single body, but one contained five frozen bodies, including two children and three adults. They appeared to have been buried immediately after death.

Tissue samples from one of the mummies, a 23-year-old female, included evidence of a hemorrhagic episode that investigators believed was caused by a sudden and lethal infection. DNA sequencing confirmed their suspicions, and also showed the presence of fragments of the variola virus, according to the Los Angeles Times.

The DNA fragments represent a new strain, now called PoxSib, but no entire viral particles survived. Before the discovery of PoxSib, the oldest samples of variola had been obtained by samples taken from patients more than 50 years ago.

"This genetic information could provide clues to past epidemics," the team wrote, the New England Journal of Medicine reports.

Investigators have been unable to determine with any precision where the strain fits into the smallpox family tree. They think it could potentially be a direct progenitor of more modern strains of the disease or part of more ancient lineage that did not cause any 20th century outbreaks.

The authors said that PoxSib might be linked to a 1714 outbreak that could have been carried into Siberia during Russian conquests of the region.