Researchers sequencing DNA from two mummified human remains in northern Chile have uncovered genetic evidence confirming that smallpox arrived in the Americas from Europe, according to reporting by Nature. The remains belonged to individuals who lived in a small settlement between 1492 and 1631, both infected with Orthopoxvirus variola at the time of their deaths.
The study, published on July 30 in Science, shows that the viral variant found in Chile split off from a European branch of the disease around the thirteenth century. The genetic sequence directly points to European colonizers as the source of the pathogen in the region.
Accidental discovery
Scientists discovered the smallpox variant while evaluating software designed to analyze ancient human DNA. The team had originally set out to study the human history of the Chilean archaeological site rather than search for ancient pathogens. Finding traces of the virus was entirely unexpected, according to study co-author Constanza de la Fuente Castro, a biological anthropologist at the University of Chile in Santiago.
Smallpox killed an estimated 300 million people in the twentieth century alone, and historical records indicate its arrival in the Americas caused catastrophic mortality across two continents. Physical archaeological evidence of viruses remains exceptionally rare, with only two other pre-twentieth-century smallpox genomes ever recovered: sequences from seventh-century Viking remains and a single sequence from a seventeenth-century Lithuanian mummy.
Genomic reduction
Comparative analysis reveals that smallpox lost active genes over centuries as it adapted to human hosts. Seventh-century smallpox genomes were larger and contained more active genes than strains circulating in the twentieth century. Terry Jones, a computational virologist at Charité — University Medicine Berlin, noted that such studies provide rare insights into pathogen history, an area where scientists currently know very little about recent viral evolution. Researchers suggest that related viruses, including the pathogen responsible for mpox, may be using a similar gene-loss mechanism today.
