Secrets of the death of Napoleon’s army: DNA reveals how bacteria and lice changed history

Researchers at the Institut Pasteur analyzed the DNA of Napoleon’s soldiers and discovered invisible diseases that contributed to the army’s 1812 disaster.

In the merciless winter of 1812, Napoleon Bonaparte’s army was retreating from Moscow, but it was not only the terrible cold and hunger that killed Europe’s bravest soldiers. More than 300,000 people lost their lives in those weeks, and until now historians have explained the disaster by the bitter cold and lack of supplies. But a recent discovery, made by analyzing the DNA of the remains of French soldiers found in Lithuania, shows that the tragedy had an unseen ally: epidemics that spread quickly among the exhausted troops, amplifying the suffering and turning the retreat into a veritable death march.

In this article, you will learn how genetic analysis of soldiers’ remains revealed the presence of fatal bacteria, how they contributed to the collapse of Napoleon’s famous army, and what these findings teach us about the role of invisible diseases in great historical events.

The withdrawal of Napoleon’s army from Russia: invisible causes and diseases. The Fatal March

Historians have debated for decades the causes of the collapse of Napoleon’s army. How was it possible for one of Europe’s most powerful military forces to fall apart almost completely in just a few months during the retreat from Russia?

More than two centuries after one of the most terrible military campaigns in history, DNA analysis offers a surprising insight: researchers have discovered, in the remains of French soldiers who died during the retreat, traces of bacterial infections that could have accelerated the tragedy.

More than 300,000 French soldiers perished during the dramatic retreat from Moscow—from cold, hunger, exhaustion, and disease. But the new findings suggest that their suffering was compounded by two newly identified bacterial infections, previously unknown to researchers.

The first clues came as early as 2006, when researchers who first analyzed the soldiers’ DNA discovered traces of two dangerous pathogens:

• Rickettsia prowazekii — the bacteria that causes epidemic typhus;
• Bartonella quintana — responsible for the so-called “trench fever”a disease common among soldiers in the wars of the 19th century.

Both infections were already suspected by historians, based on the symptoms described in the diaries of the time: high fever, skin rashes, delirium, extreme exhaustion. In addition, archaeologists had discovered body lice in the clothes and hair of the buried soldiers, confirming the presence of the parasite that transmits typhus.

DNA of Napoleon’s soldiers reveals fatal diseases. Witness over the centuries

The research team analyzed DNA taken from the remains of soldiers discovered in mass graves in Lithuania, where Napoleon’s army was decimated during the retreat from Russia. According to the scientists, the infections spread quickly among the starving and exhausted soldiers, carried by lice and made worse by the unsanitary conditions in the military camps.

The first traces of these infections were detected, as we previously mentioned, almost two decades ago, in 2006, when the analysis of ancient DNA using the polymerase chain reaction (PCR) allowed the identification of DNA fragments of some known bacteria. However, the method could not detect unknown pathogens, which made it impossible at the time to discover other infections “hidden”.

The results, recently published in the journal Current Biologyhighlighted the presence of the two already known bacteria — Rickettsia prowazekii (epidemic typhus) and Bartonella quintana (trench fever) — but also the traces of two additional pathogens, identified for the first time in the context of the campaign in Russia:

• Salmonella enterica subsp. enterica (serovar Paratyphi C) – responsible for paratyphoid fever;
• Borrelia recurrentis – which causes relapsing fever transmitted by lice.

These new pathogens may have contributed significantly to the worsening condition of the troops, hastening the collapse of the famous Grande Armée and highlighting the invisible role of disease in major historical events.

“After 20 years, the time was right to reopen the case”said Nicolás Rascovan, co-author of the study and specialist in paleogenomics at the Pasteur Institute in Paris.

Genetic analyzes rewrite the disaster of Napoleon’s army

Although historians have usually focused on freezing cold and lack of supplies as the main causes of the Napoleonic disaster, new genetic analyzes from 2025 offer a broader perspective: disease was perhaps an invisible ally of the Russian winter.

“These new results show that the reasons for the collapse of the French military are more complex than previously thought”noted the authors of the study.

“The work is a remarkable contribution — a combination of archaeology, genetics and history”added Anne Stone, a specialist in anthropological genetics at Arizona State University.

Using the most advanced sequencing techniques this time, the researchers were able to “read” traces of over two centuries old DNA and compare them to modern databases containing thousands of sequences of known pathogens. The team extracted samples from the teeth of 13 French soldiers discovered in a mass grave in Lithuania in 2002. The teeth were chosen because they best protect the genetic material, preserving “the memory” infections suffered by the body.

Through next-generation sequencing, researchers obtained millions of pieces of DNA from a single sample, allowing them to identify all the pathogens present—not just those previously suspected. The results were surprising: in addition to epidemic typhus and trench fever, traces of two more unexpected bacteria, previously unknown in the context of the Russian campaign, were discovered. These additional infections could have worsened the condition of the troops and hastened the collapse of the famed Grande Armée, researchers believe.

The invisible diseases that destroyed Napoleon’s army. The unseen death behind the legends

During the retreat from Russia, Napoleon’s army was hit from all sides: by the bitter cold, by the attacks of the Russians and, above all, by his own weak and sick body.

Lice-borne diseases—already widespread in Europe at the time—spread with devastating speed among the exhausted and starving soldiers. Each infection fueled a spiral of disaster: the sick could no longer fight or walk, and those still healthy quickly became ill, contaminating themselves through clothing, blankets and equipment.

The result was a retreat turned into an unprecedented human tragedy.

Through these paleogenomic analyses, researchers are not just filling in a chapter of history, they are rewriting the way we understand the Napoleonic disaster today. The Russian campaign was not only a strategic failure, but also a biological tragedy, in which microorganisms played a huge—but invisible—role.

The irony of history is that while the generals were planning battles and alliances, Napoleon’s real enemy turned out to be a microscopic one: an army of bacteria that won where bayonets had failed—silent but decisive.

What DNA analysis teaches us about Napoleon’s retreat

The study shows how modern science can rewrite history. More than 200 years old DNA becomes a window into the past, providing biological details where documents can no longer speak.

“This research is not just about the past,” the authors also noted, “but also about how infectious diseases shaped the fate of empires’.

For historians, it’s a humbling lesson: it’s not just military strategies or great battles that decide the course of history—but sometimes invisible organisms, carried by a single louse, can change the fate of an army.

In short, Napoleon’s retreat from Russia was not only a military defeat, but also a biological catastrophe.

Thanks to DNA, we now know that, beyond cold and hunger, bacteria were at work that silently wrote a forgotten chapter in European history—proving that the invisible can shape empires.