Ancient DNA Reveals Diseases That Decimated Napoleon’s Army

In a recent study, scientists have uncovered vital information about the illnesses that ravaged Napoleon Bonaparte’s army during its disastrous invasion of Russia in 1812. An analysis of ancient DNA retrieved from the teeth of 13 soldiers has revealed that in addition to the widely acknowledged louse-borne disease, typhus, two other significant infections were present: paratyphoid fever and relapsing fever.

Napoleon’s campaign began in the summer of 1812, with around half a million troops advancing into Russia. As the Russian forces retreated, they employed scorched-earth tactics that devastated the landscape, leaving Napoleon’s army in a beleaguered Moscow. By autumn, many of the soldiers returned to encampments along the Russian border, where approximately 300,000 men succumbed, not to enemy fire, but to a combination of harsh weather, starvation, and illness.

The new findings stem from a study published in the journal Current Biology by a research team at Institut Pasteur. They discovered fragments of microbial DNA from Salmonella enterica, known to cause paratyphoid fever, and Borrelia recurrentis, responsible for relapsing fever. These pathogens were identified in samples taken from the dental remains of soldiers unearthed in a mass grave in Vilnius, Lithuania, where over 3,000 troops were buried.

Historically, typhus has been blamed for the high mortality rate among Napoleon’s troops. This view is echoed in the writings of Stephan Talty, author of *The Illustrious Dead: The Terrifying Story of How Typhus Killed Napoleon’s Greatest Army*. Talty remarked, “There’s something perversely romantic about seeing typhus as the force that almost singlehandedly destroyed Napoleon’s army.” He noted that while the study’s sample size is limited, it strongly suggests that other infections contributed to the chaos faced by the army.

The mass grave was first discovered in 2001 during construction work at a former Soviet Army barracks. Excavations revealed the grim conditions of the burial site, where horse skeletons were found alongside human remains. The disarray suggested that bodies had been hastily disposed of, with many buried in their boots and frozen in the positions they died.

Two decades ago, an initial study focused on identifying DNA from the typhus-causing bacterium, Rickettsia prowazekii. Researchers found DNA fragments from both typhus and Bartonella quintana, known to cause trench fever. Recently, Remi Barbieri, a postdoctoral researcher at Institut Pasteur, sought to revisit these samples using modern genomic sequencing techniques.

Barbieri, along with Nicolas Rascovan, head of the microbial paleogenomics unit, employed a comprehensive approach to sequence all DNA present in the samples. This unbiased method allowed them to identify additional pathogens beyond their initial expectations. “We started like this, but we found other stuff than expected,” Barbieri noted.

The research revealed that four of the samples contained DNA related to a variant of Salmonella enterica linked to paratyphoid fever. Additionally, evidence of Borrelia recurrentis was found in one or possibly two samples. While these diseases are generally not life-threatening today, the context of Napoleon’s army was dire. Rascovan pointed out that under such desperate conditions, even a less severe pathogen could prove fatal.

Importantly, the study does not negate the presence of typhus; rather, it highlights the multifaceted suffering faced by the troops. Historical accounts describe gastrointestinal distress that could be attributed to contaminated food sources. An account from army physician J.R.L. de Kirckhoff from 1812 detailed the severe diarrhea suffered by soldiers, which he linked to consuming salted beets that had caused significant irritation to their intestinal tracts.

The insights gained from this research not only advance our understanding of historical military campaigns but also illustrate the evolving nature of microbial genetics. As the field progresses, findings like these provide a richer narrative of past events that have shaped nations. Talty succinctly summarized the implications: “This new study reinforces how impossible the whole enterprise was; in a time before railroads and antibiotics, the invasion was doomed before it even began.”