Ancient DNA reveals paratyphoid and relapsing fever among Napoleonic troops

Scientists from the Institut Pasteur genetically analyzed the remains of former soldiers who retreated from Russia in 1812. They detected two pathogens, those responsible for paratyphoid fever and relapsing fever, that correlate with the symptoms described in historical accounts. The study was published as a preprint on bioRxiv on July 16, 2025. It will be published in the journal Current Biology on October 24.

The famous Russian campaign led by Napoleon in 1812, also known as the “Patriotic War of 1812”, ended with the retreat of the French army. Scientists from the Institut Pasteur’s Microbial Paleogenomics Unit, in collaboration with the Biocultural Anthropology Laboratory at Aix Marseille University, set out to investigate which pathogens may have caused large outbreaks of infectious diseases that contributed to this historic episode. They extracted and analyzed the DNA of 13 soldiers from Napoleon’s army exhumed in Vilnius, Lithuania in 2002 during excavations led by the Aix-Marseille University team specializing in archaeoanthropology. The scientists then used next-generation sequencing techniques applied to ancient DNA to identify potential contaminants.

Their research identified the genetic signatures of two infectious agents: Salmonella enterica subsp. enterica (serovar Paratyphi C), responsible for paratyphoid fever, and Borrelia recurrentisresponsible for relapsing fever, a louse-borne disease characterized by bouts of fever followed by periods of remission. Although these two diseases are different, they can cause similar symptoms such as high fever, fatigue and digestive problems, and their simultaneous presence may have contributed to worsening the condition of the soldiers, especially as they were already weakened by cold, hunger and lack of hygiene.

Of the 13 Napoleonic soldiers exhumed in Vilnius, the teeth of four tested positive S. enterica Irregular C and two for B. recurrentis. This study provides the first genetic evidence of these two largely unsuspected infectious agents, although their exact role in the high death toll in Grande Armée during his retreat from Russia is not known. The confirmation of the presence of these two bacteria comes after a previous study that identified the typhoid agent, Rickettsia prowazekiiand the trench fever factor, Bartonella quintanapathogens long thought to be associated with the retreat based on historical evidence.

Given the small number of samples analyzed compared to the thousands of corpses found, it is impossible to determine the extent to which these pathogens contributed to the extremely high mortality observed. The scientists’ analysis was based on a limited number of samples (13 of the more than 3,000 corpses in Vilnius and about 500,000 to 600,000 soldiers in the military force, about 300,000 of whom died during the retreat).

“Access to the genomic data of pathogens circulating in historical populations helps us understand how infectious diseases evolved, spread and disappeared over time and identify the social or environmental contexts that played a role in these developments. This information provides us with valuable insights to better understand and treat infectious diseases today”, explains Nicolás Rascovan, Head of the Microbial Paleogenomics Unit at the Pasteur Institute and last author of the study.

To achieve these results, the team worked in collaboration with scientists from the University of Tartu in Estonia to develop an innovative multi-step authentication workflow, including a phylogeny-based interpretive approach for the highly degraded genome fragments recovered. This method enables scientists to pinpoint pathogens even if their DNA yields only low coverage, in some cases even indicating a specific lineage.

“In most ancient human remains, the pathogen’s DNA is highly fragmented and only present in minute amounts, making obtaining whole genomes very difficult. We therefore need methods capable of clearly identifying pathogens from these weak signals, and sometimes even tracing lineages, to explore past pathogen diversity“, he adds.

This new study reveals a correlation between historical descriptions of the diseases suffered by Napoleon’s army and the typical symptoms of paratyphoid and relapsing fever. It offers new evidence to support the theory that infectious diseases were a cause of the collapse of the 1812 campaign, along with many other factors such as exhaustion, extreme cold, and harsh conditions.

The Russian campaign led by Napoleon in 1812 ultimately ended in military defeat, resulting in the disastrous retreat of the French army. This enabled the Russian army to regain control of Moscow and dealt a huge blow to the Emperor’s strategy.