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

When Napoleon’s half-million-strong army retreated from Russia in 1812, around half the men were wiped out by disease, starvation and the extreme cold. Now, state-of-the-art DNA analysis has revealed which pathogens contributed to the catastrophe.

In the summer of 1812, Napoleon gathered as many as 600,000 troops for his invasion of Russia. However, the Tsar’s forces had abandoned Moscow and emptied the city of supplies, forcing Napoleon to retreat to the Polish border for the winter. Between October and December 1812, at least 300,000 French soldiers perished from starvation, cold and disease.

Historical reports from survivors suggested that typhus and trench fever were the main causes of death and illness among the troops, and this was backed up by genetic testing nearly two decades ago.

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

Instead, the team confirmed the presence of Salmonella enterica, which causes paratyphoid fever, and Borrelia recurrentis, which is transmitted by body lice and causes relapsing fever.

The earlier studies relied on a technique that amplifies specific DNA sequences already suspected to be present. Rascovan and his colleagues used more advanced metagenomic analysis, which can detect the genetic material of any pathogens in a sample, making it much more comprehensive.

“In light of our results, a reasonable scenario for the deaths of these soldiers would be a combination of fatigue, cold and several diseases, including paratyphoid fever and louse-borne relapsing fever,” write Rascovan and his colleagues in their report, which is yet to be peer-reviewed. The team declined to comment for this story.

While not necessarily fatal, the louse-borne relapsing fever could significantly weaken an already exhausted individual, say the researchers.

Sally Wasef at the Queensland University of Technology in Australia says the symptoms recorded in historical accounts could match several infectious diseases besides the ones suggested in the new study.

The microbial DNA recovered from the ancient individuals was in low quantities, says Wasef. “In my view, this means the results are more suggestive than conclusive.”

Wasef says more soldiers who died in 1812 need to be studied to confirm which diseases were present, as Rascovan and his colleagues also state in their study.

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

“This kind of work has strong potential to clarify the role of disease in past population declines, particularly where written records are incomplete or biased,” says Wasef.