He raised a huge army of nearly 600,000 men in the early summer of 1812 to invade Russia. The Grande Armée arrived in Moscow at the end of the summer, but found it empty. Isolated and without supplies due to the Russians’ scorched earth practice, the French chose to retreat to their winter quarters, near Poland, before the cold trapped them in the city of the tsars. The retreat was the Gallic emperor’s greatest military disaster. The very low temperatures and lack of food made the work of the pathogens easier: it is estimated that around three hundred thousand soldiers died along the way. Now, work led by researchers at the Pasteur Institute has identified two in the remains of Napoleonic soldiers. Under normal conditions, they don’t kill, but for those unfortunate people it was the finishing touch.
Among the first to enter Moscow was Dr. JRL de Kirckhoff, a doctor attached to the headquarters of the French Third Army Corps. Years later he would write a book detailing the diseases that plagued the imperial soldiers in their retreat. Specifically, it documented the prevalence of typhus, diarrhea, dysentery, pneumonia or jaundice. “At that time it had not yet been discovered that microorganisms could cause infectious diseases, so the description of a disease was based only on the symptoms,” recalls , head of the microbial paleogenomics unit at the Pasteur Institute and senior author of this research, published in .
A group of experts led by Rascovan recovered the remains of 13 Grande Armée soldiers buried in Vilnius (Lithuania) along with three thousand others. They were looking for evidence of typhus which, since Kirckhoff, is considered the disease that most punished the Napoleonic troops in their retreat. To find it, they looked at the teeth of the fallen, which is best preserved in the fossil record: “If the pathogen that infected 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 as if it were a blood sample from the individual,” explains Rascovan.
They found no trace of typhus or any other of the pathologies listed by Dr. Kirckhoff. But the teeth of four of them tested positive for Salmonella enterica Paratyphi C, from the salmonella group and which is behind paratyphoid fever. In two others, what they found was DNA Borrelia recurrentisa bacteria responsible for the so-called relapsing fever. Although these two diseases are different, they can cause similar symptoms, such as high fever, fatigue, and digestive problems. As with typhus, the vector of relapsing fever is body lice, a different species than the one that appears on the heads of many schoolchildren every September. The etiology of paratyphoid fever is different; its origin can be in unsafe water, contaminated food or contact with feces that contain the bacteria.
Under normal conditions none of these normal pathogens are fatal. “But if you are on the edge of the abyss, if you are immunosuppressed, you are starving, you are freezing to death, any little bug pushes you and you fall,” says Rascovan. Although salmonellosis due to food contamination is very common, relapsing fever disappeared from Europe more than a century ago. After the work on the causal connection between many microorganisms and disease, a few hygiene and public health measures were enough to banish a good part of them.
“There are only seven sequenced genomes of current strains of the B. recurrentis. It is so difficult to find that there is only one study that managed to isolate several, all identical,” says Rascovan. “It is very difficult to find this disease and it is found above all on the African continent, specifically in the horn of Africa.” This part of the world has been, since the 80s of the last century, the region most affected by hunger and wars. “Its sanitary conditions are perhaps more similar to those that existed at the time in Europe,” he concludes. the Pasteur Institute scientist.
That they have not found DNA of the causative agent of typhus, bacteria of the genus Rickettsiadoes not mean that Kirckhoff’s doctor was wrong in his diagnosis. In fact, in 2006, after the excavation of the Vilnius mass grave, he (from the same burial, but different individuals), identified the DNA of the Rickettsia prowazekii in three of them. In another seven, what they found was the sign of Bartonella quintana, which causes the so-called trench fever. Both bacteria use the human body louse as a transmission vehicle. The authors of this work also located several specimens of the parasite among the military’s uniforms.
Adding the teeth analyzed in 2006 and those now, it turns out that a third of the samples had some pathogen in their bodies. Although the authors are cautious and do not extrapolate, if this percentage were applied not only to the almost three thousand of those buried in Vilnius, but to the other three hundred thousand who left Moscow, but did not leave Russia alive, infectious diseases were among those that defeated Napoleon Bonaparte in the east, along with the so-called general winter and famine.
“During Napoleon’s withdrawal from Moscow in the winter of 1812, health and living conditions completely collapsed,” recalls Remi Barbieri, first author of the study, a postdoctoral fellow at the Pasteur Institute during the research. “Temperatures dropped below -30°C, food and shelter were almost non-existent, and exhausted soldiers marched hundreds of kilometers through snow and mud in tattered, lice-infested uniforms,” adds Barbieri, who delved into the history of the retreat. The combination of poor hygiene, hunger and extreme cold created the perfect breeding ground for epidemics. “Under such desperate conditions, lice- and water-borne diseases, such as typhus, relapsing fever, paratyphoid fever, and trench fever, spread rapidly through the ranks,” he details. “These multiple infections acted together, devastating an army already weakened by exhaustion and hunger, and turning the withdrawal from Moscow into one of the deadliest episodes in military history,” concludes Barbieri, now a researcher at the Institute of Genomics at the University of Tartu (Estonia).
For Francesco Maria Galassi, associate professor of anthropology and paleopathologist at the University of Łódź (Poland), the work of Barbieri and Rascován represents a great advance: “Paleogenetic analyzes allow us to better understand the role of infectious diseases in major military campaigns, such as the Napoleonic, and in many other wars throughout history.” In fact, Galassi, who was not involved in this work, recalls that “even today, infections associated with lack of hygiene and the collapse of health systems continue to be a crucial problem in current conflicts, from the Middle East to Ukraine.”
