Napoleons retreating army may have been plagued by these microbes

In 1812, the French Emperor Napoleon Bonaparte commanded an ill-fated army in a catastrophic retreat from Russia. Facing severe food shortages, the brutal onset of winter, and rampant diseases, hundreds of thousands of troops ultimately lost their lives. Recent scientific investigations have identified certain microbes that may have contributed to their plight. 

DNA extracted from the teeth of soldiers from Napoleonic times has uncovered two species of fever-inducing bacteria, as reported by geneticist Nicolás Rascovan and his colleagues from the Institut Pasteur in Paris in the October 24 issue of Current Biology. Historians have long suspected that these soldiers lived in an environment rife with infectious diseases.

According to historian Rafe Blaufarb, who specializes in the Napoleonic era, the findings correlate with historical accounts documented over two centuries ago. Medical professionals at the time noted symptoms among the soldiers, including fever, diarrhea, pneumonia, and various signs indicative of bacterial infections. This new research, which has identified two previously unconnected bacteria associated with the fateful retreat, injects some “DNA-level biological details into the narrative,” says Blaufarb, affiliated with Florida State University in Tallahassee.

Napoleon’s ambitious campaign into Russia initially seemed promising. The military leader commanded over 500,000 troops and had already achieved significant victories across Europe. However, upon reaching Moscow, they found a desolate city, laid waste by the retreating Russians. Winter was fast approaching.

With no alternatives left, Napoleon elected to retreat, Blaufarb explains. The army began a grueling withdrawal through harsh winter conditions accompanied by scarce food supplies. There is no dispute regarding the causes of death among the soldiers. The frigid temperatures, lack of sustenance, and the sheer exhaustion of trekking hundreds of kilometers over ice and snow made survival nearly impossible. “It’s just a bad, bad, bad scene. It’s as bad as it can be,” he asserts.

Illnesses also ravaged the troops. In 2006, DNA analyses from remains of Napoleonic soldiers confirmed the presence of bacteria that cause typhus and trench fever, supporting historical documentation. However, that study focused solely on those two bacteria, overlooking others that might have been present.

The current research adopted a broader strategy. “We went ahead and searched for any known pathogen,” Rascovan states. Their methodology, known as shotgun sequencing, captures numerous DNA fragments found within a sample. This encompasses DNA from the remains of soldiers, the bacteria that may have infected them, and soil microbes in the environment. It’s akin to using a large net for fishing rather than a rod aimed at a specific species.

The research team examined the teeth of 13 soldiers unearthed from a mass grave in Lithuania. In four individuals, they detected Salmonella enterica, which is responsible for paratyphoid fever. In two others, evidence of the lice-borne Borrelia recurrentis, the bacteria that causes relapsing fever, was discovered.

Rascovan stresses that their investigation examined merely a small subset of the vast number of soldiers who perished, making it impossible to determine the overall prevalence of these infections. “We aren’t asserting that these two pathogens were primary killers in the army,” he notes. Nevertheless, when combined with the intense cold and hunger, it’s likely that these and other pathogens contributed to the soldiers’ downfall.

As Blaufarb aptly summarizes: “The real mystery is how any of them managed to survive at all.”