From the pockmarked mummified pharaohs of ancient Egypt to the epic triumph of complete global eradication, smallpox had a remarkable history. But that lengthy history may be in for a massive revision, thanks to a little mummy found in the crypt of a Lithuanian church.

The mummy, thought to be of a child between the ages of two and four who died sometime between 1643 and 1665, teemed with the genetic remains of the bygone virus. That smallpox DNA was the oldest ever found—yet it was quite young, evolutionarily speaking. In fact, genetic analysis of the preserved smallpox blueprints, published Thursday in Current Biology, suggests that smallpox is just hundreds of years old, not millennia as many had thought. The finding stands to rewrite the virus' storied past.

Reports of blistering, puss-packed rashes have speckled historical records for thousands of years. The dimpled pharaohs and spotted plagues in China during the 4th century were considered proof that the smallpox virus—aka Variola—plagued humankind for a long, long time. Smallpox caused massive outbreaks throughout Europe in the 17th century and devastated populations in the New World. But, in 1796, it became the first disease for which there was a vaccine. And in 1979, smallpox was declared the first—and still only—infectious disease of humans to be globally eradicated. (Rinderpest, an infectious disease of cattle and some other animals, has also been eradicated.)

The latter part of smallpox's history is still solid, thankfully. But the ancient past may crumble to dust.

The study in Current Biology, led by researchers at McMaster University in Canada, came to the historically startling conclusion by piecing together the entire, crumbling genome of the virus collected from the Lithuanian mummy's skin—which was not pocked, oddly. To their surprise, the smallpox of the mid 17th century looked very similar to smallpox from the 20th.

The researchers next created an evolutionary family tree of the old smallpox with 42 younger relatives, plus ancient ancestors. (The other smallpox strains had been sequenced previously for research purposes from preserved isolates.) The tree revealed the pace at which the smallpox virus evolved. Knowing that rate, the researchers calculated backward to figure out when smallpox first came into existence, pegging the killer's birth to sometime between 1530 and 1654.

That's just in time for it to cause the large outbreaks in Europe during the 17th century and wreak havoc in the New World. But 1530 is long, long time after the Chinese reports and the scarred pharaohs. The authors argue that these ancient cases could easily have been misidentified cases of other rash-causing diseases.

In a press statement, co-author Henrik Poinar, the director of the Ancient DNA Centre at McMaster, said:

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. 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 chickenpox and measles?

To settle the issue, more research is necessary, of course. In particular, Poinar and his colleagues hope to track down when exactly in the 16th or 17th century smallpox appeared in humans and from where it came. A variety of pox viruses circulate in animals, but it’s unclear which one jumped to humans and what animal it was in before.

Current Biology, 2016. DOI: 10.1016/j.cub.2016.10.061 (About DOIs).