Ancient Smallpox DNA Found in Chilean Mummies: Can it Be Revived?
Smallpox remains the only human infectious disease to have been eradicated worldwide, and the newly analyzed material consists entirely of fragmented genetic sequences rather than viable, infectious viral particles.
- Scientists recovered degraded DNA fragments of the variola virus from two mummified individuals in northern Chile, dating between 1492 and 1631.
- The genetic material lacks the necessary viral machinery and intact genomes required to spontaneously cause smallpox or recreate a physical virus.
- The findings provide direct molecular evidence of how historical Chilean strains evolved, branching off from a now-extinct lineage that diverged around 1296.
For centuries, smallpox caused devastating epidemics globally. Its severe form, variola major, killed roughly 30 percent of those infected, though mortality rates fluctuated across different outbreaks and populations. Following European contact, successive epidemics in the 16th century contributed to catastrophic losses of Indigenous life in the Americas, beginning with the first documented outbreak on the island of Hispaniola in 1518. Decades later, the World Health Organization launched an intensified eradication program in 1967 combining vaccination, surveillance, and containment, which ultimately led to the declaration of global eradication in 1980 after the last naturally acquired case occurred in Somalia in 1977.
Genomic Reconstruction Versus Physical Resurrection
According to the published findings, the researchers recovered only short, chemically altered fragments of viral DNA. Because ancient DNA degrades over time, scientists must sequence surviving pieces and use computers to determine how they fit together. As a result, the reconstructed genomes represent digital assemblies of genetic information rather than physical viruses.
A functional poxvirus particle requires an intact genome alongside specific proteins and enzymes needed to reproduce inside a host cell. These ancient fragments lack that essential viral machinery. While researchers successfully assembled horsepox virus in a laboratory setting in 2018 using synthetic DNA and specialized helper poxviruses, the Chilean study involved sequencing naturally degraded historical DNA, establishing no plausible route for smallpox to return from these remains.
Pathogenesis, Evolutionary Lineage, and Clinical Context
As viruses replicate over time, genetic mutations accumulate, allowing researchers to plot samples on an evolutionary family tree. The genetic analysis shows that the two Chilean viruses belonged to a distinct, now-extinct lineage that diverged from other known variola strains around 1296. This estimated branching date predates the arrival of Europeans in the region, adding molecular context to historical records indicating how the virus spread following contact.
The mummified remains also displayed small skin lesions. Bioarchaeologist Bernardo Arriaza, a co-author of the study, had previously linked these skin marks to chronic arsenic exposure, a hypothesis supported by elevated arsenic levels found in the tissues. Because northern Chile’s rivers carried naturally occurring arsenic from the surrounding geology, contaminating local food and water sources, arsenic remains a plausible contributor. While the recovered variola DNA confirms that both individuals were infected with smallpox, researchers note that the molecular data cannot definitively establish the cause of the skin lesions or whether smallpox caused either person’s death.
Future Research Trajectory and Clinical Surveillance
The recovery of 500-year-old variola DNA highlights the power of modern paleogenomics to illuminate historical disease pathways without creating biological risks. Live variola virus is officially restricted and retained at only two high-security, WHO-designated laboratories globally for approved research.