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New discovery may reduce historic timeline of smallpox virus

The discovery of smallpox DNA in a 17th Century child mummy may reduce the timeline of this deadly infectious disease’s history, according to a research.

This highly infectious and fatal disease was eradicated in the late 1970s through a vaccination campaign on a global scale and samples of the smallpox-causing variola virus now exist only in the freezers of a secured laboratory. However, the sources of the virus are yet to be discovered.

“There have been signs that Egyptian mummies that are 3,000 to 4,000 years old have pockmarked scarring that have been interpreted as cases of smallpox,” said Ana Duggan, a postdoctoral member at the McMaster University Ancient DNA Centre in Canada.

“The new discoveries really throw those findings into question, and they suggest that the timeline of smallpox in human populations might be incorrect.”

The smallpox virus in the DNA of a skin sample of a mummified child, found in a grave underneath a Lithuanian church, could throw some light on its origin and development, said researchers in a study printed in the US scientific journal Current Biology.

The entire genome of the ancient strain of the virus was further recreated and compared with versions of the variola virus genome recording from the mid-1900s and before its eradication in the late 1970s.

According to the study, all the samples shared a common viral ancestor that originated sometime between 1588 and 1645. During that time, exploration, migration and colonisation might have aided smallpox spread all over the world.

“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 said.

The director of the Ancient DNA Centre at McMaster University said that the results project suspicion on the recorded historical evidence dating back to Egypt’s Ramses V up to the 1500s. The researchers were also able to identify distinct periods of viral evolution from the 17th-Century virus.

An evolution example occurred around the era of Edward Jenner, 18th-century pioneer of smallpox vaccine, English physician, and scientist. During this time, the variola virus apparently split into two parts, variola major and minor. That vaccination may have modified the selection pressures acting on the virus resulting in a split, according to the researchers.

“Now we know all the evolution of the sampled strains dates from 1650, but we still don’t know when smallpox first appeared in humans, and we don’t know what animal it came from, and we don’t know that because we don’t have any older historical samples to work with,” said Edward Holmes, a professor at the University of Sydney in Australia.

“Our historical knowledge of viruses is just the tip of the iceberg,” Holmes said.

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