Ancient DNA Reveals New Diseases behind Napoleon’s 1812 Russian Retreat

Napoleon’s defeat in Russia was aided by two surprising fatal illnesses

By Andrea Tamayo edited by Dan Vergano

In 1812, Napoleon Bonaparte invaded Russia with one of the largest armies in history: the “Grande Armée”, composed of approximately half a million men. But when they were forced to retreat, harsh winter conditions, famine and disease decimated the invaders. Historians estimate that around 300,000 of these men died.

Historical accounts, early DNA studies, and remains of body lice found on soldiers support the idea that typhus and trench fever contributed to the army’s downfall. However, a broader debate over the French withdrawal and the role of disease continues to fester.

“It is one of the greatest mysteries in history because ‘Why [did] Napoleon lost?’ “, says Rémi Barbieri, postdoctoral researcher at the Institute of Genomics at the University of Tartu in Estonia.

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Ancient DNA holds a clue. Genetic material recovered from historical fossils, skeletons and mummies has revealed the mysteries of our ancestors trapped in time. In a new study published in the journal Current biology, Barbieri and colleagues suggest that two previously unsuspected pathogens struck Napoleon’s massive army: Salmonella enterica, a bacteria that causes paratyphoid fever, and Borrelia recurrentis, a bacteria spread by body lice and causing relapsing fever. Both could have been fatal among soldiers suffering from starvation and intense cold.

“We expected to find the pathogens already reported,” says geneticist Nicolás Rascovan, co-author of the study and head of the microbial paleogenomics unit at the Pasteur Institute in France. But when researchers analyzed DNA from the teeth of the 13 Napoleonic soldiers, they found no bacteria that caused typhus or trench fever, two illnesses previously associated with skeletons from the site. Even if the team didn’t detect these diseases, that doesn’t mean they didn’t hit Napoleon’s army, Rascovan points out.

“What [the study] What shows is that there was a whole range of illnesses that affected these people,” he says.

“The study is very strong,” says Marcela Sandoval-Velasco, an assistant professor at the Genome Sciences Center at the National Autonomous University of Mexico, who studies molecular biology to answer questions about our past. Even though the team only had 13 samples to work with, they appreciated how the researchers clearly laid out their limitations.

In 2002, researchers excavated a site containing a mass grave housing 2,000 to 3,000 people in Vilnius, Lithuania. Napoleonic objects were scattered around the skeletons. These included ancient buttons and belts, suggesting that the remains represented soldiers from Napoleon’s army who had retreated from Russia in 1812. Rascovan and his colleagues selected only 13 individuals to preserve as many skeletons as possible. The researchers also chose this small number because they needed teeth in the best possible condition.

In the laboratory, the team opened the soldiers’ teeth. They put the scraped dental pulp into a DNA sequencing machine. Once sequenced, scientists sorted the DNA results to detect pathogenic bacteria. They compared suspected pathogenic DNA to known genomic sequences, then compared it to the two bacteria.

“By simply reading the historical accounts, [it] “It was impossible to suspect these two pathogens,” says Barbieri. But by developing this new methodology, researchers were able to identify bacteria from small fragments of DNA. “Personally, I am also very excited about the methodology.”

Looking ahead, the researchers plan to continue uncovering the role pathogens played in history, albeit in different locations. While Rascovan will focus on infectious diseases in the Americas, Barbieri will continue to focus on European history.

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