New DNA analysis of soldiers from Napoleon’s 1812 retreat from Russia has identified two previously undocumented diseases—paratyphoid fever and relapsing fever—as key contributors to the army’s massive losses, challenging long-held beliefs that typhus was the primary killer.
In the summer of 1812, French emperor Napoleon Bonaparte led an army of about half a million men in an invasion of the Russian Empire. By December, only a fraction remained, with historical records often blaming typhus for the devastation. However, a new study published in the journal Current Biology uses cutting-edge genomic technology to reexamine the causes of death, revealing a different story based on evidence from soldiers’ remains.
Researchers from the Institut Pasteur in France focused on a mass grave in Vilnius, Lithuania, where they extracted ancient DNA from the teeth of 13 soldiers. Using a method called shotgun sequencing, they analyzed highly degraded DNA fragments to identify bacterial pathogens. This approach allowed them to capture a wider range of DNA sources than older techniques like PCR, which were limited by the small size of ancient DNA pieces.
The team confirmed the presence of Salmonella enterica, which causes paratyphoid fever, a severe enteric illness. They also identified Borrelia recurrentis, the bacterium responsible for relapsing fever, which is transmitted by body lice. Both diseases would have caused recurring fevers, diarrhea, and general weakness, exacerbating the soldiers’ already dire conditions during the harsh retreat.
Contrary to long-standing assumptions, the study found no traces of Rickettsia prowazekii, the cause of typhus, or Bartonella quintana, which causes trench fever. Previous research had suggested typhus was prevalent, but the new findings indicate that multiple infectious diseases were at play. This discrepancy may be due to the advanced sequencing technology used, which can detect pathogens that earlier methods missed.
The conditions during the retreat—characterized by extreme cold, starvation, and poor sanitation—created an ideal environment for these diseases to spread. Paratyphoid fever, often from contaminated food or water, and relapsing fever, spread by lice, would have rapidly weakened the malnourished and exhausted troops. The researchers propose that a combination of these factors, along with the harsh environment, led to the high mortality rate, estimated at around 300,000 deaths.
An intriguing aspect of the discovery is that the Borrelia recurrentis strain matched one found in ancient Britain from the Iron Age, about 2,000 years earlier. This suggests that this pathogen lineage persisted in Europe for millennia, though modern strains are different. Such insights highlight how ancient DNA can reconstruct the history of infectious diseases and their evolution over time, offering a window into past epidemics.
This study not only revises our understanding of Napoleon’s disastrous campaign but also demonstrates the potential of paleogenomics to uncover hidden chapters in history. By applying modern scientific methods to ancient remains, researchers can provide more accurate accounts of past events and inform contemporary disease surveillance. Future work may explore other historical epidemics, offering lessons for public health and our comprehension of human resilience and vulnerability.