Researchers have recovered damaged genetic fragments of the variola virus—the causative agent of smallpox—from naturally mummified remains in northern Chile dating between 1492 and 1631, according to a study discussed by Professor Aris Katzourakis of the University of Oxford in The Conversation. These remains, belonging to two Indigenous people, provide the first ancient smallpox genomes recovered from the Americas, offering direct molecular evidence that illuminates how the virus spread during early European colonisation.
Ancient Smallpox Genomes Recovered in Chile
Smallpox remains the only human infectious disease completely eradicated worldwide, following a World Health Organisation (WHO) campaign that declared eradication in 1980 after the last naturally acquired case in Somalia in 1977. For centuries, the disease caused devastating epidemics with variola major killing roughly 30% of infected individuals. According to the study, the newly recovered genetic material consists solely of damaged fragments preserved for centuries in mummified tissue from northern Chile. These samples span the transition from Inca rule to the Spanish colonial period, filling a critical gap between medieval European strains and later lineages.
Evolutionary Origins and Reductive Evolution
By computationally assembling the fragmented DNA, researchers mapped the Chilean viruses onto an evolutionary family tree. According to the analysis, the strains belonged to a now-extinct lineage that diverged around 1296, branching after early medieval European genomes and before later centuries’ strains. This placement supports historical records showing smallpox arrived in the Americas following European contact, starting with the first documented outbreak on Hispaniola in 1518. Furthermore, the genomes illuminate reductive evolution, tracking how variola lost accessory genes as it specialised exclusively for human hosts, though gene loss alone does not explain the historical severity of the disease.
Did You Know?
Live variola virus is officially retained today at only two high-security WHO-designated laboratories for approved research. By contrast, the genetic material found in Chile consists only of degraded, non-viable fragments sequenced computationally without creating physical viruses.
Investigating Skin Lesions and Environmental Arsenic
The mummified remains in Chile exhibited visible skin lesions. Earlier research led by bioarchaeologist Bernardo Arriaza linked these marks to chronic arsenic exposure, supported by elevated arsenic levels found in tissue samples. According to the study, the newly confirmed variola DNA introduces smallpox as another possible explanation for the lesions. However, researchers note that the genetic data cannot definitively establish what caused those particular marks or whether smallpox caused either person’s death. Natural arsenic contamination remains plausible because local rivers carried geological runoff into regional food and water supplies.
Frequently Asked Questions
Can ancient smallpox return from these mummified remains?
No. Researchers recovered only damaged genetic fragments and short pieces of DNA lacking the viral machinery and proteins needed to reproduce, meaning they cannot spontaneously cause smallpox or create a route for its return.
How did smallpox arrive in the Americas?
Historical records note the first documented outbreak occurred on Hispaniola in 1518, and the new genetic evidence confirms the Chilean viruses are closely related to prior European strains linked to colonisation.
What is reductive evolution in the variola virus?
Reductive evolution refers to the gradual loss or disabling of non-essential accessory genes as the virus evolved to infect exclusively humans rather than multiple animal species.
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