DNA Study Reveals Hidden Bacterial Killers in Napoleon’s Army

By Manisha Sahu
America News World

October 25, 2025

A groundbreaking scientific study has shed new light on one of the most disastrous military campaigns in history — the ill-fated 1812 invasion of Russia by Napoleon’s Grand Army. While history has long focused on cold, hunger and the enemy as the main culprits, recent DNA evidence reveals that two deadly bacterial infections were stalking the troops, further undermining an army already in crisis.

The Campaign and the Grave

In the summer of 1812, Napoleon’s multi-national force, often estimated at around 500,000 men, crossed the Neman River into Russia. The plan was bold — to force Alexander I of Russia into submission and enforce the Continental System against Britain. However, the Russians withdrew, burning villages and supplies behind them, leaving the French army stretched, starving and exposed.

By the time the army retreated from Moscow and struggled back toward Lithuania and the Neman, it had been decimated. Thousands lay dead from battle, cold and starvation. Among the evidence of this tragedy is a mass grave discovered near Vilnius, Lithuania — containing more than 3,000 soldiers from Napoleon’s march.

In 2001, archaeologists unearthed this grave. More recently, scientists analysed 13 teeth — each containing dental pulp and vestiges of blood-borne pathogens — to investigate what diseases might have contributed to the army’s downfall.


The Two Bacterial Killers Revealed

Using modern next-generation sequencing on the dental pulp of those 13 soldiers, researchers found genetic traces of two specific pathogens:

Salmonella enterica (subspecies/paratyphi type) — the agent of paratyphoid fever, a disease transmitted via contaminated food or water. The infected soldiers suffered high fevers, abdominal pain, weakness and gastrointestinal distress.

Borrelia recurrentis — the agent of relapsing fever, transmitted by lice. This disease causes repeated bouts of high fever, intense fatigue, headache and nausea.


In the study, four of the 13 samples showed DNA evidence of Salmonella enterica and two samples detected Borrelia recurrentis.

Prior assumptions long had focused on typhus (caused by Rickettsia prowazekii) and trench fever (caused by Bartonella quintana) as the main infectious threats to the army. But this new evidence shows that, at least for these soldiers, those two newly identified pathogens were present and likely played a serious role. Notably, the team did not detect DNA for Rickettsia prowazekii in these samples.

Why This Matters for the 1812 Disaster

These findings matter for several reasons:

– Amplification of suffering: Even before the harsh Russian winter struck in full, soldiers were battling fevers, contaminated food, starvation and lice-born infections. The presence of paratyphoid and relapsing fever would have greatly weakened their strength, morale and ability to function. In one historical quote the army physician wrote about “large barrels of salted beets … which we drank the juice of when thirsty, greatly upsetting us and strongly irritating the intestinal tract.”

– Disease as an active combatant: The campaign is often portrayed primarily as a failure of logistics or a clash with nature (“General Winter”) and Cossacks, but this evidence shows that disease was a true combatant, silently thinning the ranks from within.

– Rewriting history with science: Modern paleogenomics allows researchers to reassess historical events not just from written records, but from molecular evidence preserved in human remains. The study underscores how technological advances are letting us reconstruct episodes long thought understood.

– Complex causation: The authors caution that these two pathogens were not the sole cause of the army’s collapse. Cold, hunger, exhaustion, lack of supplies, battlefield casualties and morale all played their parts. But adding disease to the mix deepens our understanding of how the disaster unfolded.


A Closer Look at Context and Conditions

Sanitation & Lice: With men packed into camps with poor hygiene, lice-borne disease like relapsing fever could spread easily. Once a soldier is weakened, even minor illnesses become dangerous when supplies and medical care are lacking.

Contaminated food and water: Historians have long documented how Napoleon’s troops ran out of regular rations, resorted to consuming whatever they could find, and sometimes drank from unsafe sources. Under such conditions, food- and waterborne pathogens like Salmonella enterica thrive.

Already at the brink: When you factor in frost, hunger, exhaustion, competition for dwindling resources and enemy action, you create a scenario where any additional strain — like an infectious disease — can tip the balance toward disaster. As the lead researcher noted, “we are talking about an army that was in such a very fragile situation—any infectious disease can really kill someone.”


What the Study Can and Cannot Tell Us

Strengths

Use of unbiased genome sequencing on ancient DNA allows detection of pathogens not previously considered.

Provides direct molecular evidence linking specific diseases to remains of the army.


Limitations

The sample size is small: only 13 teeth from one mass grave of over 3,000 bodies at that site; the broader presence of those pathogens across the entire army is unknown.

Only certain pathogens leave detectable DNA in dental pulp; other diseases (e.g., cholera or tuberculosis) might have been present but undetected.

Cannot determine how many soldiers were infected, how many died specifically because of these pathogens, or their relative impact compared with cold, hunger and combat.



Why This Matters for Us Today

While this is a story about armies and wars from over two centuries ago, it resonates today for reasons beyond historical curiosity:

It shows the persistent importance of infectious disease in human events — not just in wars, but in migrations, societies under stress and humanitarian crises.

It underscores how combining disciplines (history, archaeology, genetics) can yield richer, more nuanced understandings of the past.

It reminds us that beyond the visible threats (weapons, weather, terrain), unseen biological forces can dramatically influence outcomes.


Closing Thoughts

The story of Napoleon’s 1812 campaign has long been told as a tale of overreach, harsh winter, stretched lines of supply and military miscalculation. What this new work adds is a reminder that the collapse was also biological. The men marching into Russia were not just fighting enemy armies and the elements—they were battling microscopic foes, in the form of paratyphoid fever and relapsing fever, that compounded every other hardship.

As one historian noted, the study is “an interesting historical case study … of what … an extraordinary episode of human suffering.”  The brave and doomed soldiers of Napoleon’s army may have died for many reasons; now, thanks to tiny traces in ancient teeth, we understand just a little more of how and why.

For readers of America News World, this story is more than a dramatic episode in European history—it is a powerful lesson in how unseen forces shape human destiny.