DNA analysis reveals what really killed Napoleon’s army in 1812

When the army of half a million Napoleon withdrew from Russia in 1812, about half of the men were destroyed by illness, famine and extreme cold. Now, the analysis of advanced DNA has revealed which pathogens have contributed to the disaster.

In the summer of 1812, Napoleon brought together up to 600,000 soldiers for his invasion of Russia. However, the Tsar forces had abandoned Moscow and emptied the city of supplies, forcing Napoleon to retire to the Polish border for the winter. Between October and December 1812, at least 300,000 French soldiers died of famine, colds and illness.

The historical relationships of the survivors suggested that the typhus and the fever of the trenches were the main causes of death and illness among the troops, and this was supported by genetic tests almost two decades.

Now, Nicolás Rascovan at the Institut Pasteur de Paris and his colleagues examined the DNA of the teeth of 13 of the soldiers buried in Vilnius, Lithuania, where many soldiers died during the retreat, and found no proof of typhus or fever of the trench.

Instead, the team confirmed the presence of Salmonella Entericawhich causes paratyphoid fever, and Recurrent Borreliawhich is transmitted by the lice of the body and causes a fever relapse.

Previous studies have relied on a technique that amplifies specific DNA sequences already suspected of being present. Rascovan and his colleagues used a more advanced metagenomic analysis, which can detect the genetic material of all pathogens in a sample, which makes it much more complete.

“In the light of our results, a reasonable scenario for the death of these soldiers would be a combination of fatigue, cold and several diseases, in particular paratyphoid fever and fever revised by the thumb”, write Rascovan and his colleagues in their report, which has not yet been examined by peers. The team refused to comment on this story.

Although it is not necessarily fatal, the relapse fever transmitted by the thumb could considerably weaken an already exhausted individual, say the researchers.

Sally Wasef of Queensland University of Technology in Australia claims that the symptoms recorded in historical accounts could match several infectious diseases in addition to those suggested in the new study.

The microbial DNA recovered from ancient individuals was small quantities, explains Watef. “In my opinion, this means that the results are more suggestive than conclusive.”

Wasef says that more soldiers who died in 1812 must be studied to confirm what diseases were present, because Rascovan and his colleagues also say it in their study.

Research highlights the potential of new tools to identify possible infectious agents in historical populations, explains Watef. She would like to see the methods used to study diseases in the post-contact populations of the Americas or Australia.

“This type of work has great potential to clarify the role of the disease in previous population decreases, especially when written recordings are incomplete or biased,” explains Watef.