Ancient mummy DNA in Chile shows that colonisation brought smallpox to the Americas

Published on 31/07/2026 - 16:08 GMT+2

Ancient mummy DNA recovered in Chile offers the clearest genetic evidence yet that European colonisation brought this disease to the Americas, according to a new study.

Smallpox was one of the deadliest diseases in human history before it was eradicated in 1980, largely thanks to vaccination. For centuries, the virus had killed about one-third of the people it infected and left most survivors with deep and sometimes disfiguring scars.

The first historically documented smallpox outbreak in the Americas occurred in 1518, during the Spanish conquest of the Caribbean. The disease then spread rapidly across North, Central and South America, killing millions of people, particularly among Indigenous populations who had no prior immunity.

In the new study, published in the journal Science, researchers from Trinity College Dublin examined 13 bone samples previously collected from an archaeological site at Camarones, in northern Chile.

The analysis provides the strongest genetic link yet between smallpox found in the Americas and strains that circulated elsewhere in the world, offering new insights into how the virus reached remote populations following European colonisation, the authors said.

They found evidence of two smallpox infections in ancient DNA from the leg bone fragments of an adult man and woman, who were between 18 and 35 years old and whose cause of death was likely smallpox.

By dating the remains and analysing the viral DNA, the scientists concluded that the two individuals likely died between 1492 and 1631. They also compared this version of the smallpox virus with other known strains and found that it fell genetically between medieval European strains and later variants.

This was important molecular evidence, suggesting that the strains of smallpox infecting people in the Americas descended from strains circulating in Europe.

“Nobody would ever question that smallpox came to this hemisphere from colonisation, but this proves it,” said Patricia Foster, a biologist at Indiana University, who did not participate in the study.

Exactly which population brought smallpox to the Americas from Europe remains unclear, said the study authors. Settlers came in different waves to the Americas following the explorations of Christopher Columbus in the Caribbean in 1492 and Amerigo Vespucci along the South American coast about a decade later.

The disease may also have spread via Africa during the expansion of the transatlantic slave trade.

The infections were identified in an area with no previous record of smallpox, raising new questions about how the virus reached such a remote part of South America. It may have spread along Indigenous trading networks that predated the arrival of Europeans.

Studying different strains of the virus also allowed scientists to trace how it evolved over time, including the loss or inactivation of certain genes that may have helped it adapt to humans.

The findings point to how devastating the disease was across the Americas, wiping out entire populations and leaving them vulnerable to European conquest, said study coauthor Constanza de la Fuente Castro, a biological anthropologist at the University of Chile.

“It wasn't just cultural or demographic. It's literally written into biological evidence that we can still recover and read today,” de la Fuente Castro said.