Ancient mummy DNA recovered from northern Chile has yielded the firmest genetic evidence yet that European colonization brought smallpox to the Americas, according to research published in Nature and reported in bostonglobe.com. Scientists examined 13 bone samples previously collected from an archaeological site at Camarones, finding evidence of smallpox infections in leg bone fragments belonging to an adult man and woman who lived between 1492 and 1631.
Ancient DNA From Chilean Mummies Provides Proof of Smallpox Origins
The two individuals, a woman estimated to be between 30 and 35 years old and a young man around 18 to 20 years old, were found at an archaeological site called Camarones 9 near the Pacific coast. Researchers concluded the two likely died during the same outbreak or were infected by the same strain circulating through the region, as their nearly identical viral genomes ruled out separate exposures. The discovery provided researchers with the first known ancient smallpox genomes in the Americas, a novel strain designated as CAM9, as detailed by martincid.com.
Accidental Discovery Alters Evolutionary Timeline
The finding came by accident while researchers were testing DNA analysis software to study the human history of the archaeological site, as reported by scientificamerican.com. Biological anthropologist Constanza de la Fuente Castro of the University of Chile in Santiago noted that finding traces of the disease was entirely unexpected. The project was originally intended to examine population history rather than search for pathogens, but a suggestion by Bruno Romero González of martincid.com to screen for pathogens redirected the study.
By comparing the Chilean variant to other ancient and modern smallpox genomes, scientists found that the new lineage branched off after medieval European strains but before those that gave rise to modern smallpox. This placement fits the virus neatly between European strains from medieval times and later versions, confirming that European colonizers were the source of smallpox in the region. The genomes also preserve an intermediate stage in the virus’s specialization for humans, illustrating how variola disabled unnecessary genes as it adapted to its host.
Historical Context and Unanswered Questions
Before it was eradicated in 1980 largely thanks to vaccination, smallpox was one of the deadliest diseases in human history, killing about one-third of the people it infected. While historical records and missionary reports documented how colonial epidemics devastated Indigenous populations who had never been exposed to the virus, written accounts of smallpox in Chile begin much later. The Camarones 9 site itself has no historical record of documented smallpox outbreaks.
Researchers suggest the virus may have reached the remote southern location by spreading along pre-existing Indigenous trading networks that predated the arrival of Europeans. However, study authors note that the foundation of the study relies on just two individuals from one site. While sufficient to establish CAM9’s existence and evolutionary position, additional genomes from other sites and time periods will be needed to determine how many separate introductions occurred, how rapidly the virus spread, or precisely which population brought the disease across the Atlantic following the explorations of Christopher Columbus and Amerigo Vespucci.
