Analysis of the DNA of an ancient mummy found in Chile has provided the most solid scientific confirmation to date that smallpox was introduced to the Americas by European colonization.
Before being eradicated in 1980, mainly through vaccination, smallpox represented one of the most lethal diseases in human history. For centuries, the virus claimed the lives of approximately a third of those infected and left many with permanent, often disfiguring scars.
Evil epidemics ravaged Asia and Europe, later spreading to the Americas. There, colonial documents, official records, and missionary testimonies reported the deaths of millions and the annihilation of indigenous communities without prior exposure to the pathogen.
Now, irrefutable scientific proof of its spread has emerged: an investigation into Chilean mummies establishes the most robust genetic connection ever identified with the virus, similar to variants circulating outside the Americas. This deepens understanding of how the disease reached isolated areas due to colonization, as explained by geneticist Shigeki Nakagome, from Trinity College Dublin. This new evidence, dated June 13, 2024, not only corroborates historical records, but also details the molecular mechanism of the disease’s introduction, filling in gaps about the initial trajectory of smallpox on the continent and reinforcing the direct biological impact of colonization on native populations.
For the recent study, Nakagome and his team analyzed 13 bone samples previously collected at an archaeological dig in the Camarones region of northern Chile.
Researchers identified evidence of two smallpox infections in ancestral genetic material obtained from bone fragments from the legs of an adult man and woman.
Based on dating of the remains and genetic analysis, scientists determined that both individuals likely died between 1492 and 1631. There was also a comparison of the genes of this variant of smallpox with others, resulting in a precise fit between medieval and later European lineages. This represents relevant molecular evidence, pointing out that the smallpox strains that reached the Americas initially developed in Europe.
“No one would question that smallpox arrived in this hemisphere through colonization, but this proves it,” said Patricia Foster, a biologist at Indiana University who was not involved in the new research, published Thursday in the journal Science.
Those responsible for the study indicated that uncertainty persists about which population group introduced Old World smallpox to the Americas. Europeans arrived on the continent in different phases, after the expeditions of Christopher Columbus in the Caribbean, in 1492, and of Amerigo Vespucci along the South American coast, approximately ten years later. The disease may also have spread from Africa, as part of the expansion of the slave trade.
Smallpox contamination in South America was detected in a region with no previous record of the disease. This raises new questions about how the virus reached such a southern area — suggesting possible spread through indigenous trade routes that already existed long before the arrival of Europeans.
The investigation of several strains of the virus also allowed scientists to determine its chronological evolution, observing the deactivation of certain genes that made it more efficient in its lethal capacity.
In addition to validating the trajectory of smallpox, the research also illuminates the human impact of the disease. The two infected individuals examined were between the ages of 18 and 35, and smallpox was the likely cause of their deaths.
The findings demonstrate how catastrophic the disease proved to be in the Americas, decimating entire communities and making them susceptible to European domination, said work co-author Constanza de la Fuente Castro, a biological anthropologist at the University of Chile.
“It wasn’t just a cultural or demographic issue. It’s literally written in biological evidence that we can still recover and interpret today,” added de la Fuente Castro.
