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When Napoleon and his legion of multinational soldiers retreated from Russia in 1812 in the face of dwindling supplies and fierce Russian resistance, little did they know how much worse was yet to come.
While withdrawing from Russia, at least half of the 600,000-strong force were ravaged by the extremes of winter, starvation, and disease. A new study has now identified which pathogens helped decimate the weakened forces.
"It's very exciting to use a technology we have today to detect and diagnose something that was buried for 200 years," says metagenomics researcher Nicolás Rascovan of the Institut Pasteur in France.
Physicians at the time documented typhus, with symptoms that include fevers, headaches, and rashes. But researchers found no traces of the bacterium Rickettsia prowazekii, which would have been responsible for the disease.
After extracting and analyzing ancient DNA from the teeth of 13 soldiers they instead found evidence the men suffered from a combination of paratyphoid caused by a strain of Salmonella enterica, and a relapsing fever caused by a bacterium called Borrelia recurrentis, which is transmitted by body lice .
"While not necessarily fatal, the louse-borne relapsing fever could significantly weaken an already exhausted individual," the researchers explain in their paper.
The scientists caution that just because their analysis did not detect typhus doesn't mean it didn't contribute to the infamous loss of soldiers, as they only took samples from 13 individuals. Over 3,000 bodies lie in the mass graves found in Vilnius, Lithuania, in 2001.
Other researchers have pointed out several diseases match the historical accounting of symptoms, including typhus.
Many of the men were buried in their uniforms and with horses, too. The lack of weapons suggests these people did not die in battle, Barbieri and his team explain.
"The analysis of a larger number of samples will be necessary to fully understand the spectrum of epidemic diseases that impacted the Napoleonic army during the Russian retreat," they write.
"In light of our results, a reasonable scenario for the deaths of these soldiers would be a combination of fatigue, cold, and several diseases, including paratyphoid fever and louse-borne relapsing fever."
This paper has been uploaded to Current Biology.
An earlier version of this article was published in August 2025.