Toward the end of his leadership, Napoleon Bonaparte, the French emperor, launched an ambitious campaign in 1812, leading an army of more than 500,000 soldiers into Russia. Within half a year, after a grueling retreat, only a fraction—tens of thousands—managed to make it back to France.

This ill-fated military effort is remembered as one of history’s most devastating campaigns, with massive casualties resulting not only from combat, but also from famine, freezing temperatures, and widespread disease outbreaks.

Recently, scientists analyzing DNA from the remains of these soldiers uncovered evidence of more than one infectious disease. In addition to known illnesses, two previously undetected bacterial infections were identified. The research was published in the journal Current Biology.

“For a long time, typhus was thought to be the single disease responsible for most deaths,” explained lead researcher Rémi Barbieri, formerly a postdoctoral fellow at the Institut Pasteur and currently affiliated with the University of Tartu in Estonia. However, the findings revealed something unexpected—other serious infections may have played a key role in the high mortality rate.

Skeleton discovered in modern-day Russia is believed to belong to one of Napoleon's generals, shedding light on this turbulent period.

The two newly detected pathogens—Salmonella enterica and Borrelia recurrentis—are responsible for causing paratyphoid and relapsing fever, respectively. These bacteria were identified from dental remains of soldiers found in a mass grave site discovered in 2001 in Vilnius, Lithuania.

These discoveries not only deepen our understanding of historical events but also highlight the power of modern genetics to unlock secrets of the past, according to the research team.

A Complex Web of Illness

When Napoleon's army arrived in Moscow, they found the city deserted. The Russian forces had burned crops and abandoned supplies, leaving the French troops with no food or decent clothing. Facing a bitter winter, they began their retreat under extremely difficult conditions.

A study in 2006 first identified the presence of Rickettsia prowazekii—the bacteria responsible for typhus—in the remains of the fallen soldiers. However, technology at the time limited deeper analysis. In the recent study, scientists used high-throughput sequencing, which processes millions of DNA fragments at once, making it possible to analyze degraded samples over 200 years old.

“These powerful sequencing tools allow us to analyze a vast amount of ancient DNA,” said study coauthor Nicolás Rascovan, head of the Microbial Paleogenomics Unit at the Institut Pasteur. “Research like this paints a clearer picture of past epidemics and helps us understand how those events influenced present-day disease patterns.”

The scientists examined genetic material from 13 individuals and surprisingly found no typhus traces in those samples, though this does not necessarily contradict earlier studies. The sample size was small, and the researchers acknowledged that its results alone cannot determine disease prevalence in the entire army. “Our findings confirm the presence of multiple infectious diseases at this site,” Rascovan noted. He also suggested that other undetected illnesses may have affected the troops.

Cecil Lewis, an expert in ancient DNA who specializes in the human microbiome, remarked that while the results were not entirely unexpected, the study marked an important advancement in understanding the downfall of Napoleon’s troops. Lewis, who serves as vice president of academics at the Oklahoma School of Science and Mathematics, was not involved in the research.

“We’re entering an era where ancient DNA research offers new insights into historical events,” Lewis said. “It sheds light on the evolution of diseases over time, revealing a lineage between now-extinct pathogens and those we deal with today. Understanding these patterns is key to managing future health threats.”

Although paratyphoid and relapsing fever still exist, they are now rare and much less deadly. Napoleon himself survived the campaign, but the heavy losses his army suffered led to the decline of his empire in the years that followed.

“It’s astonishing how rapidly technology has advanced since 2006,” Rascovan commented. “What seemed impossible a few years ago is now achievable, and I'm excited to see what developments lie ahead.”

Written by Taylor Nicioli, a freelance journalist based in New York.