VILNIUS, Lithuania — More than two centuries after Napoleon Bonaparte's disastrous invasion of Russia, new DNA evidence is shedding light on the invisible enemies that decimated his Grande Armée. Researchers analyzing ancient genetic material from soldiers' teeth have uncovered traces of two deadly fevers that likely contributed to the staggering losses during the 1812 retreat, challenging long-held assumptions about the primary culprits behind the army's collapse.
The study, published in the journal Current Biology, examined dental remains from 13 soldiers discovered near Vilnius, where thousands perished in mass graves during the brutal winter retreat. According to the findings, the soldiers were afflicted by pathogens causing paratyphoid fever and relapsing fever, diseases that would have spread rapidly amid the squalid conditions of the fleeing army.
"Ever since 1812, people have thought that typhus was the most prevalent disease in the army," said Nicolás Rascovan, head of the microbial paleogenomics unit at the Institut Pasteur and a lead author of the study. Using advanced shotgun sequencing techniques, his team identified "two previously undocumented pathogens" in the samples.
Specifically, the researchers detected Salmonella enterica from the Paratyphi C lineage, the bacterium responsible for paratyphoid fever, as well as Borrelia recurrentis, which causes louse-borne relapsing fever. These infections, Rascovan explained, thrive in environments with "very poor sanitary conditions or hygiene," conditions that were rampant among Napoleon's troops as they trudged through snow and mud, weakened by hunger and exposure.
The symptoms described in historical accounts—fever, diarrhea, and debilitating weakness—align closely with those caused by these diseases, the study noted. "A reasonable scenario for the deaths would be a combination of fatigue, cold, and several diseases, including paratyphoid fever and louse-borne relapsing fever," the researchers wrote. They added that while relapsing fever is "not necessarily fatal," it could "significantly weaken an already exhausted individual."
Napoleon's campaign began in June 1812 when he led an estimated 600,000 soldiers across the Niemen River into Russian territory, assembling what was then the largest army in European history. Aimed at forcing Tsar Alexander I to comply with France's continental blockade against Britain, the invasion initially progressed with sweeping victories. However, as the French advanced toward Moscow, Russian forces employed a scorched-earth strategy, burning crops and villages to deny the invaders supplies.
By September, Napoleon entered a deserted Moscow, but the city was soon set ablaze, reportedly by Russian saboteurs. With no decisive battle and winter approaching, the emperor ordered a retreat in October. What followed was one of the most harrowing episodes in military history: blizzards, subzero temperatures, and relentless Cossack attacks whittled away at the army. Historians estimate that by the time the remnants crossed back into friendly territory in December, around 300,000 men had died, many from disease, starvation, and cold rather than direct combat.
The Vilnius site, where the studied remains were found, holds particular significance. In 2002, construction workers unearthed a mass grave containing thousands of skeletons, believed to be from Napoleon's soldiers who succumbed during the retreat. The Lithuanian capital, then part of the Russian Empire, served as a brief staging point, but overcrowding and lack of provisions turned it into a death trap.
Rascovan's team chose teeth for analysis because dental pulp preserves ancient DNA well, shielded from environmental contamination. Their method allowed for a broad scan of genetic material, revealing the presence of these specific bacteria in multiple samples. "We confirmed the presence of Salmonella enterica belonging to the Paratyphi C lineage," Rascovan told reporters, highlighting the bacteria's role in causing severe gastrointestinal illness.
Relapsing fever, transmitted by body lice, would have been especially virulent in the lice-infested ranks. Soldiers, packed together in unheated shelters or marching in tattered uniforms, provided ideal conditions for louse-borne diseases to spread. Historical diaries from the campaign describe men shivering with recurrent fevers, their bodies racked by chills and sweats, symptoms that match Borrelia recurrentis infection.
This new research builds on but also contrasts with earlier studies. A 2006 investigation, which examined remains from the same Vilnius graves, detected evidence of typhus and trench fever in four out of 35 individuals. That study, limited by the DNA sequencing technology available at the time, used targeted probes rather than the comprehensive shotgun approach employed now.
Rascovan emphasized that the older findings remain valid and complement the current ones. "Finding four different pathogens in such a number of individuals, it really shows that there were a high prevalence of infectious diseases of all kinds," he said. His team's analysis found no traces of typhus or trench fever in their 13 samples, suggesting that while typhus may have been present, other fevers played a more significant role than previously thought.
While not necessarily fatal, the louse-borne relapsing fever could significantly weaken an already exhausted individual.
The discrepancy highlights the patchy nature of ancient DNA preservation and the challenges of sampling from mass graves. Experts say the combined evidence paints a fuller picture of a multifaceted health crisis, where multiple infections compounded the effects of the Russian winter and logistical failures.
Beyond rewriting the medical history of the 1812 campaign, the study underscores the timeless threat of infectious diseases in warfare. "Even an emperor, it seems, can’t outmarch a microbe," noted Freddie Clayton, the journalist who reported on the findings for NBC News. Modern parallels abound, from the role of disease in World War I trenches to recent outbreaks in conflict zones.
Researchers hope to expand their analysis to more samples, potentially uncovering additional pathogens. For now, the discovery serves as a reminder of how microscopic foes can topple empires. As Rascovan put it, the Grande Armée met its match not in muskets or cannon fire, but in the relentless assault of bacteria that no general could command.
The implications extend to paleopathology, the study of ancient diseases, offering insights into how pathogens have evolved over time. Paratyphoid fever, for instance, remains a concern in parts of the developing world today, while relapsing fever has largely been controlled through improved hygiene. By tracing these lineages back to 1812, scientists can better understand their historical spread and mutations.
Historians, too, may revisit accounts of the retreat. Eyewitness reports from figures like General Armand de Caulaincourt, Napoleon's aide-de-camp, described soldiers dropping dead from "fever" without specifying types. The new data provides a scientific backbone to these narratives, suggesting that paratyphoid's diarrhea and relapsing fever's episodic attacks accelerated the army's disintegration.
In Vilnius, the mass graves continue to yield secrets. Local archaeologists have preserved many remains, and ongoing excavations could provide more material for genetic studies. Lithuanian officials have expressed interest in collaborating on further research, viewing it as a way to honor the dead and educate about this chapter of European history.
As the bicentennial of the campaign passed in 2012, interest in Napoleon's Russian debacle has endured, inspiring books, films, and debates about hubris in leadership. This latest scientific twist adds a layer of humility: even the most ambitious conquerors are vulnerable to the smallest of adversaries.
Looking ahead, Rascovan's team plans to apply similar techniques to other historical sites, potentially revealing disease patterns in events like the Black Death or colonial expeditions. For Napoleon's ill-fated army, the story is far from over—each DNA sequence unearthed brings the past a little closer, illuminating the human cost of ambition on a microbial scale.