It has been known for a very long time that the ancient rashes that scar the faces of Egyptian mummies are evidence that smallpox ravaged the region more than three thousand years ago. A study of viral DNA extracted from a child mummy that dates back to the 17th century—the oldest known sample of any virus—suggests that the most lethal form of smallpox emerged in humans much more recently. This was just in time for it to hitchhike with explorers to the New World and decimate populations all over the world.
According to historian Kyle Harper of the University of Oklahoma in Norman, who was not involved in the work, if the team’s analysis is correct, it would “challenge many of the current beliefs about one of the most notorious pathogens in human history.”
Accidentally, the group working on the new study managed to isolate the virus that causes smallpox. Researchers from Lithuania and Finland collected tissue from the mummified remains of a young child. The remains were discovered in the crypt of the Dominican Church of the Holy Spirit in Vilnius, which dates back to the mid-17th century. The researchers were hoping to obtain DNA from a less common virus. Ana Duggan, a postdoc working in Hendrik Poinar’s ancient DNA lab at McMaster University in Hamilton, Canada, received a shocking revelation after the researchers sent a sample of the child’s DNA there. The child did not have any obvious signs of pox on their body. The team reports in today’s issue of Current Biology that the sample contained a significant amount of variola, the virus that is responsible for causing smallpox. The researchers were able to create a high-quality copy of the virus’s genome for the first time ever from such an old virus because they had access to a large quantity of the virus. (The most ancient pathogens sequenced have been derived from bacterial DNA, including one that was responsible for spreading the plague over a thousand and six hundred years ago.)
The team was also taken aback by the discovery that the ancient viral DNA extracted from the child mummy shared many distinct characteristics with modern strains of the variola virus, including several mutations, which indicated that the two viruses were likely closely related. The researchers constructed a family tree consisting of 49 modern strains as well as the ancient strain that was found in the child, and they followed the lineage of evolution of all of the strains back to a common ancestor that emerged between 1530 and 1654 C.E.
This date is astonishingly recent, falling only a few decades or so before the time of the child mummy and a significant amount of time after the dynasties of Egyptian pharaohs. It is also much later than other accounts of epidemics that have been attributed to smallpox by historians, such as pustulous rashes from the fourth century China and the Antonine Plague in Rome in 165 C.E. According to Poinar, these individuals may have been infected with chickenpox, measles, or a different type of pox that was less fatal but has since become extinct. Alternatively, they may have been infected with a pox that has since become extinct.
But where did this new strain of variola that was so lethal emerge from during the 16th and 17th centuries? There is a chance that it was latent in an animal host and then jumped to humans. This is one possibility. Another possibility is that the variola virus that infects humans underwent a mutation that made it more lethal. According to Poinar, even if it did originate in animals, the virus could linger in their populations and have the potential to infect humans once more.
“raises interesting questions about the diversity of strains that were present in the prevaccination era,” says Anne Stone, a biological anthropologist at Arizona State University in Tempe. “The study raises interesting questions about the diversity of strains that were present in the prevaccination era.” According to Ann Carmichael, a professor emerita of history at Indiana University in Bloomington, the first thing that needs to be done in order to solve this mystery is to reproduce the team’s result. She personally searched through the death records in Italy and France, but she was unable to locate any real evidence of smallpox epidemics that occurred prior to the 17th century. Carmichael has a premonition that researchers studying ancient DNA will set out on a similar journey. They are going to search in every location where mummies are known to exist.
