Napoleon Bonaparte assembled a massive army of approximately 600,000 men in the summer of 1812 to invade Russia. Although the Grande Armée reached Moscow by late summer, they found the city deserted. Isolated and lacking supplies due to the scorched earth tactics employed by the Russians, the French decided to retreat to their winter quarters near Poland before the harsh cold trapped them in the Russian capital. This withdrawal became one of the greatest military disasters for the French emperor.
During this retreat, extreme cold and food shortages allowed pathogens to thrive, resulting in an estimated 300,000 soldiers perishing along the way. Recent research led by scientists from the Institut Pasteur has identified two bacteria present in the remains of French soldiers. While these pathogens typically do not cause death under normal circumstances, they proved fatal for the ill-fated troops.
Among the first to enter Moscow was Dr. J.R.L. de Kirckhoff, a physician assigned to the headquarters of the Third Corps of the French Army. Years later, he documented the diseases that plagued the imperial soldiers during their retreat, including typhus, diarrhea, dysentery, pneumonia, and jaundice. “At that time, it was not yet understood that microorganisms could cause infectious diseases, so the description of an illness was based solely on symptoms,” noted Nicolás Rascovan, head of the microbial paleogenomics unit at the Institut Pasteur and senior author of the study published in Current Biology.
A team led by Rascovan recovered the remains of 13 soldiers from the Grande Armée buried in Vilnius, Lithuania, among approximately 3,000 others. Their goal was to find evidence of typhus, which, since Kirckhoff”s time, has been regarded as the disease that most severely affected Napoleon”s troops during their retreat. To locate the pathogen, they examined the soldiers” teeth, which preserve well in the fossil record. “If the pathogen infecting any of them was circulating in the blood at the time of death, the bacterial DNA would be preserved in the blood that reaches the dental pulp, acting as a blood sample of the individual,” explained Rascovan.
During the invasion, the French army experienced minimal casualties in their few encounters with the Russians. However, the extreme conditions and high mortality rate during their retreat were captured by Adolph Northen in his painting “The Retreat from Russia.” The researchers did not find traces of typhus or any other diseases listed by Dr. Kirckhoff. However, the teeth of four soldiers tested positive for Salmonella enterica Paratyphi C, which is associated with paratyphoid fever. In another two cases, they discovered DNA from Borrelia recurrentis, the bacterium responsible for relapsing fever.
While these diseases differ, they can cause similar symptoms, including high fever, fatigue, and digestive issues. Like typhus, the vector for relapsing fever is body lice, a different species than those often found on schoolchildren”s heads each September. The origin of paratyphoid fever can be traced back to unsanitary water, contaminated food, or contact with feces containing the bacteria. Under normal circumstances, neither pathogen is fatal. “But if you are on the brink of disaster, immunocompromised, starving, and freezing, any little bug can push you over the edge,” Rascovan stated.
Although salmonellosis from food contamination is common, relapsing fever has not been seen in Europe for over a century. Thanks to the work of Louis Pasteur and Robert Koch on the causal relationship between many microorganisms and diseases, a few hygiene and public health measures have eradicated a significant number of these illnesses. “There are only seven sequenced genomes of current strains of B. recurrentis. It is so difficult to find that only one study has successfully isolated several, all identical,” Rascovan remarked. “This disease is hard to find and is primarily present in Africa, especially in the Horn of Africa.” This region has been the most affected by famine and wars since the 1980s.
“Their sanitary conditions might resemble those that existed in Europe during that time,” concluded Rascovan. The absence of DNA from the typhus-causing agent, bacteria from the genus Rickettsia, does not imply that Dr. Kirckhoff made an incorrect diagnosis. In fact, in 2006, after excavating a mass grave in Vilnius, a study of the dental remains of 35 soldiers from the same burial site identified Rickettsia prowazekii DNA in three of them. In another seven, signals of Bartonella quintana, which causes trench fever, were found. Both bacteria use body lice as transmission vehicles. The study”s authors also found several specimens of the parasite among the soldiers” uniforms.
The teeth of the soldiers are crucial; the team has recovered pathogen DNA from the dental pulp. In the image, a French soldier”s jawbone is displayed alongside a button from his uniform, which belonged to the 17th Infantry Regiment. Combining the teeth analyzed in 2006 with those from the current study reveals that one-third of the samples contained some pathogen in their bodies. Although the authors are cautious and refrain from extrapolating, if this percentage were applied not only to the nearly 3,000 buried in Vilnius but also to the other 300,000 who left Moscow but did not return alive from Russia, infectious diseases played a significant role in defeating Napoleon Bonaparte in the east, alongside the harsh winter and famine.
“During Napoleon”s retreat from Moscow in the winter of 1812, sanitary and living conditions completely collapsed,” recalled Remi Barbieri, the first author of the study and a postdoctoral fellow at the Institut Pasteur during the research. “Temperatures dropped below -30 °C, food and shelter were almost nonexistent, and exhausted soldiers marched hundreds of kilometers through snow and mud in tattered uniforms infested with lice,” Barbieri added, who delved into the history of the retreat. The combination of poor hygiene, starvation, and extreme cold created the perfect breeding ground for epidemics. “In such desperate conditions, diseases transmitted by lice and water, such as typhus, relapsing fever, paratyphoid fever, and trench fever, spread rapidly among the ranks,” he detailed. “These multiple infections acted in concert, devastating an already weakened army due to exhaustion and hunger, turning the retreat from Moscow into one of the deadliest episodes in military history,” concluded Barbieri, now a researcher at the Institute of Genomics at the University of Tartu in Estonia.
For Francesco Maria Galassi, an associate professor of anthropology and paleopathology at the University of Łódź in Poland, the work of Barbieri and Rascovan represents a significant advancement: “Paleogenetic analyses allow for a better understanding of the role of infectious diseases in major military campaigns, such as the Napoleonic Wars, as well as in many other conflicts throughout history.” In fact, Galassi, who did not participate in this work, recalls that “even today, infections related to poor hygiene and the collapse of sanitary systems remain a critical issue in current conflicts, from the Middle East to Ukraine.”
