Smallpox could be way younger than we thought

Those ancient smallpox victims may have succumbed to something else entirely

The rise and fall of smallpox may be a short blip instead of a long reign. It was officially eradicated in 1980, but the disease we killed off may have been only a couple hundred years old, not many thousands as previously thought.

Historical records have long suggested that smallpox is an ancient disease dating back to about the 4th century in China, Egypt, and India. A new genetic analysis of a mummified Lithuanian child dates the smallpox virus to only around the late 16th century, suggesting that modern forms of smallpox are at most a few hundred years old. They estimated some strains may be as little as 200 years old. Ancient accounts of the disease relied on descriptions of the main symptom—namely, the rash that it produces—to assign a diagnosis. When smallpox was still around, doctors used laboratory tests to confirm that the rash and high fever were being caused by the variola virus, which causes the disease we call smallpox, as opposed to some other poxvirus.

Drawings of Aztec smallpox victims
These drawings of Aztec smallpox victims might depict the very early form of virulent smallpox that spread around the world Wikimedia Commons user Graham Beards

Smallpox has been a cemented part of history books for many years. It helped shape the course of human exploration. As European explorers reached far areas of the globe they carried the disease with them, decimating native people as they went. Central America lost a huge chunk of its inhabitants to the disease when Hernán Cortés and his fellow Spaniards arrived, making their conquest all the easier. That epidemic lies just beyond the estimate for the smallpox common ancestor.

The international group of authors published their analysis in *Current Biology * and estimated the modern strain of variola virus originated around 1588-1645. A slightly looser estimate puts it back as far as 1530. The Spanish conquest of Central American occurred in the 1520s.

Their estimate doesn’t preclude smallpox as the cause of the Central American epidemic. But it does cast much of the disease’s history into a new light. If early cases of the disease were, in fact, smallpox, this new genetic analysis suggests that they were caused by other forms of smallpox that weren’t around in the 20th century.

Crypt where the Lithuanian mummy was found
This is the crypt where the Lithuanian mummy was found, preserved well enough for the variola virus to be genetically analyzed Kiril ?achovskij

They may also have been less virulent—not as contagious nor as deadly. Major epidemics of smallpox started around the 16th century and became more commonplace in the 17th and 18th centuries. The Lithuanian child mummy that this group studied died in the mid 1600s, and so may have died from a more modern, virulent strain of the disease. Two major groups of smallpox strains, one highly virulent and the other more benign, separated at some point between the 16th and 18th centuries. This split coincides with an era of worldwide exploration and slave trade, which likely contributed to the evolution of different types of smallpox virus.

None of this can override the historical record by itself, but with more research the history of smallpox might have a very different timescale than we thought. We may have to literally rewrite history, or at least the textbook version. Or maybe just Wikipedia.

Sara Chodosh

Sara Chodoshis an associate editor at PopSci where she writes about everything from vaccine hesitancy to extreme animal sex. She got her master's degree in science journalism at NYU's Science Health and Environmental Reporting Program, and is getting a second master's in data visualization from the University of Girona. Contact the author here.