The Impact of Smallpox on Indigenous Peoples in the Americas
Historians have long believed that Europeans brought smallpox to the Americas, leading to the deaths of countless Indigenous peoples. Recent genetic evidence supports this theory.
A new study published in Science revisits two mummies found in northern Chile in 1990, utilizing advanced DNA analysis. The individuals, who likely passed away between the late 15th and early 17th centuries, carried a previously unknown strain of the variola virus responsible for smallpox, closely related to strains affecting Europeans in that same era.
Shigeki Nakagome, a geneticist at Trinity College Dublin and co-author of the study, remarked, “This discovery provides the first molecular confirmation that smallpox was carried to the Americas during the colonial period. Beyond tracking the disease’s entry, our research illuminates how smallpox evolved.”
Unexpected Discoveries
Interestingly, the team did not initially set out to find ancient smallpox DNA. Instead, they aimed to examine the ancestry and population history of northern Chileans, as noted by co-author Constanza de la Fuente Castro, an anthropologist at the University of Chile. The mummies, including a woman in her 30s and a man in his 20s, are believed to have been Inca and were buried in an Indigenous site.
Further DNA analysis revealed evidence of smallpox in both mummies—nearly identical strains—suggesting they perished during the same outbreak, according to de la Fuente Castro. Earlier examinations had identified skin lesions, which were thought to be caused by arsenic exposure, but now seem to indicate smallpox infections.
A Lost History
The genetic findings also enabled the researchers to trace the evolution of the variola virus globally. The analysis revealed that the strain evolved between the medieval European varieties and those emerging later. Strikingly, the virus evolved at a slower rate during the colonial expansion, likely due to a lack of immunity in Indigenous populations, which allowed it to spread with minimal adaptation, as explained by co-author Lara Cassidy, also a geneticist at Trinity College Dublin. This pattern shifted around the 19th century when Edward Jenner introduced the smallpox vaccine.
With a vaccine now in place, the virus began evolving again, although the overall rise in vaccination provided increased protection to the populace. In 1980, the World Health Organization declared smallpox officially eradicated.
Another Beginning
Experts not involved in the study praised the findings. Ana Duggan, acting chief at the Public Health Agency of Canada’s National Microbiology Laboratory, noted that while two genomes may seem limited, they significantly enhance our understanding of variola viruses in historical contexts. Patricia Foster, a biologist at Indiana University, expressed that while it’s well-established that smallpox arrived from colonization, this research offers concrete proof.
Bruno Romero González, the lead author and PhD student at Trinity College Dublin, added that these findings illustrate how major historical events—including colonization, population changes, and vaccination—likely influenced the evolution of one of humanity’s deadliest diseases, highlighting how ancient DNA can help clarify ongoing historical debates.
