The real killer of Napoleon’s army revealed by DNA testing
Napoleon Bonaparte’s catastrophic invasion of the Russian Empire remains one of the greatest military errors in history. In the summer of 1812, the French emperor crossed the Neman River into Eastern Europe with more than 615,000 soldiers of the Grande Armée, intending to force his enemy to accept a continental blockade against the United Kingdom. In less than six months, more than half a million of Napoleon’s soldiers succumbed to hunger, hypothermia and disease.
The failed excursion is still studied today, with historical accounts suggesting that typhus was a leading cause of death. However, recent microbial analysis conducted on the remains of soldiers from the Grande Armée indicates that at least two other pathogens played a central role in the deaths of thousands. According to a study published today in the journal Current biologyit was not necessarily typhus that killed thousands of Napoleon’s men, but rather a pair of unpleasant illnesses known as enteric and relapsing fever.
It’s easy to see why the typhus theory remained popular for decades. According to early accounts from French doctors and soldiers, the infectious disease may have killed more soldiers than the Russians themselves. The discovery of the main vector of typhus – body lice – on body remains coupled with traces of DNA from the bacterial cause of typhus (Rickettsia prowazekii) also supported this narrative.
In recent years, technological advances have opened the door to a re-examination of the Grande Armée’s losses. It is with this in mind that a team of microbial paleogenomics led by Nicolás Rascovan of the Institut Pasteur in France decided to revisit the common narrative. To do this, they would need to examine the remains of some of the many victims of the Napoleonic excursion. Their sources came from a mass grave located in Vilnius, Lithuania, a stop during the French army’s retreat in December 1812. After extracting and sequencing DNA from the teeth of 13 soldiers, they then cleaned their samples of any surrounding environmental contamination and looked for evidence of disease-causing bacteria.
None of the men had any trace of typhus. Instead, the team discovered fragments of Enteric Salmonella And Recurrent Borrelia. The first bacteria is responsible for enteric or typhoid fever, while the second causes relapsing fever. Interestingly, both pathogens help explain the earlier theory of typhus. The name typhoid fever refers to its symptomatic similarities (“typhoid” means “typhus-like” after all) and was not recognized as a distinct disease until later in the 19th century. Meanwhile, relapsing fever is often transmitted by body lice.
Rascovan’s team also dismissed previous work that detected R. prowazekii or trench fever (Bartonella Quintana) among soldiers buried in the same mass grave. They believe the reason for earlier misidentifications likely came from the use of different sequencing technologies. Previous studies relied on the polymerase chain reaction (PCR), a system that multiplies copies of a single DNA segment when the source material is limited.
“Ancient DNA is heavily degraded into pieces too small for PCR to work,” Rascovan said in a statement. “Our method is able to cast a wider net and capture a greater number of DNA sources based on these very short ancient sequences.”
The study authors also made another unexpected discovery. The tension of B. recurrentis that we see on Napoleon’s soldiers dates back to the same lineage that other researchers have recently discovered and which is thought to have existed around 2,000 years earlier in Iron Age Britain. Although every day B. recurrentis The strain sequenced so far belongs to an entirely different lineage, the one identified by Rascovan’s team appears to have at least survived long enough to devastate the French army.
“It’s very exciting to use technology that we have today to detect and diagnose something that has been buried for 200 years,” Rascovan said.
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