Scientists from the Institut Pasteur have uncovered new evidence showing that deadly infections likely contributed to the massive losses during Napoleon’s retreat from Russia in 1812.
In a groundbreaking study, researchers analyzed the remains of French soldiers and discovered traces of two serious diseases: paratyphoid fever and relapsing fever. These findings help explain the symptoms described in eyewitness accounts of the disastrous military campaign.
The study was first released as a preprint on July 16, 2025, and later published in the journal Current Biology. The research team included scientists from the Institut Pasteur’s Microbial Paleogenomics Unit and the Laboratory of Biocultural Anthropology at Aix Marseille University.
They examined ancient DNA samples from 13 French soldiers whose remains were found in a mass grave in Vilnius, Lithuania, in 2002.
Napoleon’s invasion of Russia, known as the “Patriotic War of 1812,” ended with a catastrophic retreat. His once-powerful army, made up of about 500,000 to 600,000 troops, lost nearly half its men. Many soldiers died from cold, hunger, and exhaustion. Now, this new study adds strong evidence that disease was also a major factor.
The scientists used advanced gene-sequencing tools to study the soldiers’ bones and teeth for signs of infection. They found DNA from two different disease-causing bacteria. Four soldiers had Salmonella enterica Paratyphi C, which causes paratyphoid fever. Two soldiers had Borrelia recurrentis, the bacterium behind relapsing fever.
Relapsing fever is spread by lice and causes waves of fever and recovery, while paratyphoid leads to severe stomach issues and weakness. Together, these infections would have made already suffering soldiers even more vulnerable.
This is the first time these two pathogens have been genetically confirmed in soldiers from Napoleon’s army. Although the sample size was small—just 13 soldiers out of thousands buried in Vilnius—the results match past reports of fevers and disease among the troops.
Earlier research had already found other disease agents, like the bacteria that cause typhus and trench fever, making it clear that Napoleon’s forces were hit by multiple epidemics during the retreat.
While this study doesn’t reveal how widespread the infections were, it shows that deadly microbes played a role alongside harsh weather and poor living conditions. It’s estimated that about 300,000 soldiers died during the campaign, many never making it back to France.
Lead scientist Nicolás Rascovan explained that studying ancient DNA helps scientists learn how diseases evolve and spread. This knowledge can improve how we fight infections today. His team used a special method that helps detect even small amounts of damaged DNA, allowing them to identify ancient bacteria and even track specific strains.
Matching the scientific results with historical records, the researchers found that the symptoms of the diseases they detected—fever, fatigue, and digestive problems—closely matched what survivors of the 1812 retreat had described.
Napoleon’s defeat in Russia was a turning point in history, leading to the decline of his empire. This study shows that alongside the freezing temperatures and lack of food, infections may have been a silent enemy that helped bring down one of history’s greatest armies.
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The study is published in Current Biology.
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