When Napoleon Bonaparte led his Grand Army into Russia in 1812, he commanded the largest military force Europe had ever seen — an estimated 600,000 men. By the time his battered troops stumbled out of an empty Moscow months later, fewer than 100,000 remained. Just 30,000 would barely make it back home alive.
This was one of the worst debacles in military history. Napoleon’s army’s collapse is traditionally pinned on starvation, freezing temperatures, and an outbreak of typhus. But a new study of DNA extracted from the teeth of soldiers buried in mass graves outside Vilnius, Lithuania, points to two previously undocumented infections.
Instead of the expected culprit — Rickettsia prowazekii, the bacterium responsible for typhus — scientists found two microbial foes: Salmonella enterica (causing paratyphoid fever) and Borrelia recurrentis (the agent of louse-borne relapsing fever).
“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,” write Rémi Barbieri, Nicolás Rascovan, and their co-authors from the Institut Pasteur.
A Fractured Alliance Turns to War
The roots of Napoleon’s disastrous Russian campaign lay in a fragile peace. After the 1807 Treaty of Tilsit, France and Russia were nominal allies. But the arrangement had been little more than a diplomatic performance. Tensions festered. Russia chafed under Napoleon’s Continental System, the economic embargo meant to isolate Britain. In 1810, Alexander I retaliated by imposing tariffs that crippled French trade. Napoleon, in turn, seized the duchy of Oldenburg, a territory connected to the Russian royal family.
Then came the final insult: the failure of Napoleon to secure a Russian bride. The refusal of Grand Duchess Anna Pavlovna’s hand was the last straw.
In 1811, Russia braced for war. Alexander made peace with Turkey and allied with Sweden. Though he failed to rally Prussia and Austria, he prepared his nation for the coming storm. France, meanwhile, gathered an army of staggering size—some 600,000 men drawn from across Europe, though fewer than half were French. Among them marched Prussians, Austrians, Italians, Poles, Dutch, and Swiss. Few spoke the same language. Fewer still would survive.
Napoleon’s armies entered Russian territory in late June, 1812 under a blistering sun. The emperor expected a swift and decisive victory — perhaps one great battle to bring Alexander to the negotiating table. He never got it.
Instead, Russian generals — first Barclay de Tolly, then the aging and calculating Mikhail Kutuzov — refused to offer a direct engagement. They withdrew deeper into Russia, torching villages, destroying supplies, and luring Napoleon ever farther from his own lines. The Russian Second Army, under Prince Pyotr Bagration, skillfully joined with Barclay’s forces. Napoleon’s plan to crush them separately failed.
As the French pressed forward, they found not glory but emptiness. Russian peasants had fled. Crops were torched and wells were poisoned. The heat was stifling. Water was scarce. Disease began to gnaw at the ranks. Soldiers from foreign contingents, unused to the harsh conditions and unfamiliar with the foraging tactics required, deserted in droves.
The army dwindled as it advanced.
The Battle that Left a Mark
In early September, the Russians finally turned to fight. On the road to Moscow, near the village of Borodino, Kutuzov made a stand.
The battle on September 7 was the bloodiest single day of the Napoleonic Wars. Both sides suffered staggering losses — more than 70,000 killed, wounded, or missing. Napoleon claimed victory, but his army was shattered. He declined to commit his elite Imperial Guard, perhaps fearing it was his last reserve. The Russians retreated in good order. Moscow lay on the horizon undefended, but the price had been high.
When Napoleon entered Moscow on September 14, he found no tsar, no delegation, and no surrender. The city was empty. Then it began to burn.
For days, fire ravaged the ancient capital. Flames lit the sky. Whether set by Russian arsonists or accidental sparks, the result was the same: Napoleon’s supposed prize was a smoking ruin, devoid of supplies or strategic value.
Still, he waited for Alexander to sue for peace. No offer came.
The Retreat into Nightmare
On October 19, with snow in the air and his men starving, Napoleon gave the order to retreat.
The retreat from Moscow marked the true beginning of the catastrophe. The Grand Armée, now only 110,000 strong, retraced its path through the barren countryside it had already stripped bare. The Russian army shadowed them. Peasant militias and Cossack raiders attacked from the flanks. The temperature plunged, with snow covering the corpses that now lined the road.
The climax came in late November at the Beresina River. Russian forces blocked the crossings. Napoleon’s engineers built makeshift bridges under enemy fire. Thousands drowned or were cut down. The river choked with bodies. It was the final death knell of the invasion.
Napoleon escaped, but barely. On December 6, he left what remained of his army and rode for Paris. He arrived on December 18 to find his political enemies already spreading rumors of his death.
His arrival had been preceded by an announcement in the Moniteur, the official government news organ, which blamed the French defeat not on the Russian army but instead on the Russian winter. The announcement concluded with a stunning tribute to Napoleon’s egotism: “His Majesty’s health has never been better.”
Elsewhere, on December 14, Marshal Ney led the last survivors across the Niemen River. Fewer than 30,000 remained of the original 600,000. Many were maimed. Few were whole.
A Campaign Derailed by Disease
For decades, historians and microbiologists have pointed to typhus and trench fever — spread by lice in crowded, filthy conditions — as the prime culprits behind the Grand Army’s collapse. Earlier DNA studies using PCR-based methods reported fragments of Rickettsia prowazekii (typhus) and Bartonella quintana (trench fever), apparently confirming that view.
But the new study, relying on a more powerful and comprehensive DNA survey technique, found no trace of either microbe.
Instead, in four of the 13 sampled individuals, the scientists identified genetic material from Salmonella enterica serovar Paratyphi C — an ancient strain that causes paratyphoid fever, a gastrointestinal infection spread through contaminated food or water. In another two individuals, they found sequences matching Borrelia recurrentis, the bacterial cause of relapsing fever, which is transmitted by lice.
“While not necessarily fatal,” the authors note, “the louse-borne relapsing fever could significantly weaken an already exhausted individual.”
These infections likely didn’t act alone. The researchers emphasize that they cannot rule out the presence of other pathogens, including typhus. But their metagenomic approach — which captures all DNA present in a sample, rather than only targeting known suspects — provides stronger authentication for what was truly there.
A Diary of Suffering
The clinical picture revealed by these pathogens aligns closely with firsthand accounts from the retreat. In 1812, French army physician J.R.L. de Kirckhoff reported diarrhea and dysentery as common among soldiers in Lithuania, writing:
“We encountered in almost every house, from Orcha to Wilna, large barrels of salted beets… which we ate and drank the juice of when we were thirsty, greatly upsetting us and strongly irritating the intestinal tract.”
This description closely mirrors the symptoms of paratyphoid fever, including stomach pain, diarrhea, and fever. Yet at the time, doctors lacked the tools to distinguish between different fevers—typhus, typhoid, relapsing—based on symptoms alone.
Indeed, the bacterial agents behind these diseases weren’t even discovered until the late 19th and early 20th centuries.
In the cold, filthy trenches of Vilnius, where the remains of Napoleon’s soldiers were discovered, lice were ubiquitous, and the men were malnourished, dehydrated, and sleep-deprived. This was an ideal environment for both relapsing fever and gastrointestinal infections to spread.
Not The Full Picture
The team’s findings came from just 13 teeth, recovered from a mass grave in Vilnius, Lithuania. These teeth, with their dense structure, can preserve traces of pathogens that once circulated in the blood.
Using tools like KrakenUniq and BLASTN for DNA classification, the researchers authenticated old DNA from the pathogens and placed the strains on the bacterial family tree. They showed that the paratyphoid strain belonged to the Paratyphi C lineage, which has appeared in ancient European remains before. The Borrelia recurrentis strain they found seems to have descended from a lineage that had persisted in Europe for millennia, stretching back to the Iron Age.
Still, they caution that their sample size is small and that more research is needed.
Ancient DNA studies have revealed the long presence of paratyphoid strains in Europe, including during the Roman period and the Middle Ages. And while relapsing fever is rare today in most of Europe, it once lurked in the seams of every soldier’s uniform.
“Our study confirms the presence of two previously undocumented pathogens,” the authors write, “but 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.”
The past may not always repeat itself, but it does sometimes linger — in mass graves, in old bones, and, now, in fragments of ancient DNA. And when we listen carefully, as these researchers have, the microbes tell their story too.
Armies through history, from ancient Rome to 20th‑century conflict, have often suffered more from disease than from bullets. Napoleon’s retreat was no exception. He lost tens of thousands to fever, poisoning, and dehydration — many more than to direct combat.
Today, disease remains a threat in armed forces: from malaria in tropical deployments to novel infections like Ebola and Hantavirus. Napoleon’s army reminds us that even great commanders can be undone by illness.
The new findings appeared in the preprint server bioRxiv.
