A 200-year-old mystery over what destroyed Napoleon’s armies as they retreated from their invasion of Russia may finally have been solved after DNA analysis of remains found in Lithuania.

Having assembled his Grande Armée of more than 600,000 men, it took less than three months for Napoleon’s forces to reach Moscow by September 1812 but they arrived to find the city abandoned and ablaze.

The French armies remained in Moscow for a month waiting for a peace deal from the tsar that never came before Napoleon decided to withdraw to Poland. As they retreated between October and December 1812, the French forces were harried by Russian attacks, beset by starvation and battered by the harsh winter. Disease was also thought to have played a central role in decimating the troops. Typhus was thought to be the main culprit after the discovery of lice on remains.

Researchers have now extracted DNA from the teeth of 13 French soldiers buried in Vilnius, the capital of Lithuania, and found signs of two strains of fever-causing bacteria that are likely to have overwhelmed the exhausted and beleaguered troops.

“The team found traces of Salmonella enterica, a bacterium that causes enteric fever, and Borrelia recurrentis, responsible for relapsing fever, which is also transmitted by body lice,” according to the French study, which was published in the journal Current Biology. The study found that it was likely the soldiers suffered from a form of paratyphoid fever.

“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,” the researchers said.

Nicolás Rascovan, from the Institut Pasteur in France, said: “It’s very exciting to use a technology we have today to detect and diagnose something that was buried for 200 years.”