Smallpox, a deadly viral disease long thought to have appeared in human populations thousands of years ago in ancient India, Egypt and China, may actually have emerged in more recent times, a new study suggests.
The pathogen that caused millions of deaths worldwide may not be an ancient disease but a much more modern killer that went on to become the first human disease eradicated by vaccination, researchers said.
The findings raise new questions about the role smallpox may have played in human history and fuels a longstanding debate over when the virus that causes smallpox, variola, first emerged and later evolved in response to inoculation and vaccination, they said.
"Scientists don't yet fully comprehend where smallpox came from and when it jumped into humans," said senior study author, Hendrik Poinar from McMaster University in Canada.
"This research raises some interesting possibilities about our perception and age of the disease," said Poinar.
Smallpox, one of the most devastating viral diseases ever to strike humankind, had long been thought to have appeared in human populations thousands of years ago in ancient Egypt, India and China, with some historical accounts suggesting that the pharaoh Ramses V - who died in 1145 BC - suffered from smallpox.
Scientists extracted the heavily fragmented DNA from the partial mummified remains of a Lithuanian child believed to have died between 1643 and 1665, a period in which several smallpox outbreaks were documented throughout Europe with increasing levels of mortality.
The smallpox DNA was captured, sequenced and the ancient genome, one of the oldest viral genomes to date, was completely reconstructed.
There was no indication of live virus in the sample and so the mummies are not infectious.
Researchers compared and contrasted the 17th Century strain to those from a modern databank of samples dating from 1940 up to its eradication in 1977.
The study shows that the evolution of smallpox virus occurred far more recently than previously thought, with all the available strains of the virus having an ancestor no older than 1580.
"This study sets the clock of smallpox evolution to a much more recent time-scale" said Eddie Holmes, a professor at the University of Sydney in Australia.
"Although it is still unclear what animal is the true reservoir of smallpox virus and when the virus first jumped into humans," said Holmes.
Researchers also discovered that smallpox virus evolved into two circulating strains, variola major and minor, after English physician Edward Jenner famously developed a vaccine in 1796.
The findings were published in the journal Current Biology.
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