How Napoleon’s army met its doom: DNA reveals surprise illnesses had a role
Some disease-ridden French soldiers have just received a new diagnosis — although it comes about two centuries too late. While retreating from Moscow in 1812, French emperor Napoleon I lost most of his army to hunger, illness and the frigid Russian winter. Now, analysis of some of the fallen soldiers’ DNA has uncovered two unsuspected diseases that plagued the troops1.
The results reveal that the reasons for the army’s demise might be more complex than was once thought, the authors report today in Current Biology. “This paper will be really interesting to history buffs,” says Anne Stone, who researches anthropological genetics at Arizona State University in Tempe. “This study was done beautifully.”
Fatal march
Historians had long debated the factors that led to the collapse of Napoleon’s army. Eventually, in 2006, researchers studying DNA in some of the soldiers’ remains identified two disease agents2: Rickettsia prowazekii, which causes typhus, and Bartonella quintana, which causes trench fever. These two had already seemed likely culprits on the basis of symptoms described in historical records and the discovery of body lice, which spread typhus, on the soldiers’ remains.
However, these identifications relied on the polymerase chain-reaction (PCR) technique, which creates millions of copies of a short DNA segment. That technique allows researchers to detect DNA sequences for specific pathogens, so it excelled at verifying the presence of microorganisms that historians had already thought were present in the remains. But it isn’t as well suited for identifying unsuspected diseases.
After 20 years, it felt like the right time to return to the mystery, says Nicolás Rascovan, a co-author of the new study and a palaeogenomicist at the Pasteur Institute in Paris. Armed with new techniques that can screen ancient DNA for any known pathogen, the team set out to identify other microbes that might have afflicted the troops. The researchers extracted DNA from the teeth of 13 fallen soldiers whose remains had been excavated in Lithuania in 2002. They then used next-generation techniques to sequence millions of different DNA fragments from a sample. That allowed the authors to look for a wide array of pathogens all at once.
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