A team of researchers has uncovered the first direct genetic evidence identifying two infectious diseases that caused the terrible losses of Napoleon Bonaparte’s army in its retreat from Russia in 1812. The findings, released as a preprint on bioRxiv, challenge a long-standing ᴀssumption that epidemic typhus was the major cause of death among the retreating army.

Napoleon’s retreat from Moscow, by Adolph Northern, 1851. Credit: Public domain / Wikimedia Commons

By advanced genetic sequencing of DNA extracted from the teeth of 13 soldiers buried in a mᴀss grave in Vilnius, Lithuania, researchers confirmed the presence of Salmonella enterica Paratyphi C, the bacterium responsible for paratyphoid fever, in four of them, and Borrelia recurrentis, the louse-borne relapsing fever pathogen, in two. No authenticated DNA from Rickettsia prowazekii (typhus) or Bartonella quintana (trench fever) was found, overturning decades of ᴀssumptions based on previous, less accurate research.

Napoleon’s invasion of Russia in June 1812 started with an army of as many as 600,000 men from all over Europe. Early hopes of a swift triumph unraveled when Russian commanders Mikhail Kutuzov and Barclay de Tolly refused direct confrontation, retreating into the depths of Russia and destroying supplies. By the time Napoleon eventually reached Moscow in September, the city had been evacuated and soon engulfed in flames. Faced with no peace offer from Tsar Alexander I and the arrival of winter, Napoleon gave the retreat order in mid-October.

The retreat was calamitous. Harried by Russian troops, Cossacks, and militiamen, frostbitten and starving soldiers trudged back along bare roads. Disease broke out under the cold, unsanitary conditions. French army doctor Dr. J.R.L. de Kirckhoff reported widespread diarrhea and dysentery in Lithuania, blaming some of it on soldiers consuming salted beetroot and brine from abandoned homes. These symptoms align with paratyphoid fever, an illness that causes fever, abdominal pain, diarrhea or constipation, and weakness.

Napoleon in burning Moscow by Albrecht Adam, 1841. Public domain

Relapsing fever, caused by lice that infested dirty uniforms, would have contributed to the misery, causing cycles of high fever, muscle pain, and exhaustion. While neither disease in itself was necessarily life-threatening, when combined with malnutrition, hypothermia, and battlefield wounds, they were a ᴅᴇᴀᴅly mix. Skeletal analysis of the Vilnius remains indicated little evidence of violent trauma, but rather illness, cold, and starvation as the primary killers.

The genetic analysis used a metagenomics approach, identifying all the DNA in the samples rather than targeting specific pathogens. Tools such as KrakenUniq and BLASTN confirmed ancient microbial DNA through damage patterns and positioned the pathogens into long-established European lineages. The Paratyphi C strain found among the soldiers has also been identified in ancient skeletons from the Roman era, and the Borrelia recurrentis lineage goes as far back as the Iron Age.

Battle of Moscow, 7th September 1812 by Louis-François Lejeune, 1822. Public domain

The Vilnius mᴀss grave holds more than 3,000 sets of remains from Napoleon’s retreat, but only 13 individuals have been sampled so far. The researchers stress that more extensive sampling is needed to fully map the range of the disease that ravaged the Grande Armée. They caution that typhus and other diseases cannot yet be ruled out.

Historians estimate that fewer than 30,000 of the soldiers returned from the retreat — a fraction of the initial army. The new research points out that Napoleon’s defeat was not only due to Russian war strategy or winter conditions, but also to microscopic enemies thriving in the turmoil of war.

This study not only solves part of a 200-year-old mystery but also reminds us that, in war, disease has repeatedly proven to be as ᴅᴇᴀᴅly as any weapon.

More information: Barbieri, R., Fumey, J., Kabral, H., Scheib, C. L., Signoli, M., Costedoat, C., & Rascovan, N. (2025). Paratyphoid fever and relapsing fever in 1812 Napoleon’s devastated army. doi:10.1101/2025.07.12.664512