Scientists have uncovered new DNA evidence that challenges long-held assumptions about Napoleon’s disastrous 1812 invasion of Russia. As his Grande Armée – nearly half a million strong – advanced towards Moscow, it faced fierce resistance, dwindling supplies and the onset of a brutal winter.
By the time the troops began their retreat, starvation and disease had taken hold. Now, analysis of soldiers’ remains suggests that, rather than typhus being the main force behind the army’s demise, a mix of infectious diseases may have helped decimate the French Emperor’s troops.
In a new study led by Dr Nicolás Rascovan at the Institut Pasteur in Paris, researchers extracted genetic material from the teeth of 13 soldiers buried in a mass grave in Vilnius, Lithuania.
Using ancient DNA sequencing, they found no trace of typhus, the infection caused by Rickettsia bacteria long believed to have ravaged Napoleon’s troops. Instead, the team identified two different pathogens: Salmonella enterica, which causes enteric fever (such as typhoid), and Borrelia recurrentis, responsible for relapsing fever.
“What our study adds on top of what has been done before is that now we can go and redefine pathogens that were not necessarily suspected before,” Rascovan told BBC Science Focus.
Previous studies had used PCR testing – the same method used in modern COVID-19 tests – to search only for specific microbes. The technology available today allows scientists to “cast a wider net,” Rascovan said, and identify fragments of any microbial DNA present.
“These techniques allow us to see things we just wouldn’t have been able to 10 years ago,” Rascovan said.
“If we put together work from previous studies plus the study that we’re doing now, we find a total of four different diseases present in just a few individuals. What does it indicate? That not one single pathogen killed all these 3,000 people, but rather that these people were infected with the whole range of pathogens.”
In other words, conditions were so grim for Napoleon’s army as they fell back from Russia that a whole host of diseases were able to thrive among the troops. If one disease didn’t get you, another almost certainly would.
The findings also revealed that one strain of Borrelia recurrentis found in the remains was genetically identical to one circulating in Iron Age Britain 2,000 years earlier – a lineage that has since vanished.
“This was an ancestral branch of this pathogen that doesn’t exist anymore, or if it does, we don’t know where it’s hiding,” Rascovan said. “From this, we learn that something in the hygiene and sanitary conditions changed, alongside the arrival of antibiotics, in the last 200 years to completely eradicate the disease – which was, until very recently, widespread.”
For Rascovan, these ancient microbes are more than grim curiosities. They’re historical witnesses. “Of course, for the person who was infected, this was not amazing,” he said. “But for me, it’s amazing because I can reconstruct things.
“These pathogens are allowing us to really learn something about the populations and the dynamics of the populations in the past.”
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