Toronto, Dec 10 (IANS): Smallpox, a 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, suggests genetic research.

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 Pharaoh Ramses V - who died in 1145 BC -- suffered from smallpox.

The new findings, published in the journal Current Biology, fuel a longstanding debate over when the virus that causes smallpox, variola, first emerged and later evolved in response to inoculation and vaccination.

"This study sets the clock of smallpox evolution to a much more recent time-scale" said Eddie Holmes, Professor at the University of Sydney, Australia.

In an attempt to better understand its evolutionary history, and after obtaining clearance from the World Health Organisation (WHO), the team of scientists extracted the heavily fragmented DNA from the partially mummified remains of a Lithuanian child.

The child is believed to have died between 1643 A.D. and 1665 A.D., 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.

Researchers compared and contrasted the 17th century strain with those from a modern databank of samples dating from 1940 up to its eradication in 1977.

Strikingly, the research showed 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.

"So now that we have a timeline, we have to ask whether the earlier documented historical evidence of smallpox, which goes back to Ramses V and includes everything up to the 1500s, is real," senior author of the study Hendrik Poinar from McMaster University in Hamilton, Canada, said.

"Are these indeed real cases of smallpox, or are these misidentifications, which we know is very easy to do, because it is likely possible to mistake smallpox for chicken pox and measles," Poinar pointed out.

"It is still unclear what animal is the true reservoir of smallpox virus and when the virus first jumped into humans," Holmes noted.