Death of failed French forces in 1812 finds new explanations
Near the end of his reign, in 1812, French emperor Napoleon Bonaparte led an army of more than half a million men in an invasion of Russia. It is estimated that, six months later, after the army was forced to retreat, only tens of thousands of its soldiers will have managed to return to France.
The deaths of hundreds of thousands of soldiers were attributed to the fighting, as well as to hunger, cold and a typhus epidemic, making this one of the most costly battles in history.
Now, investigators have found evidence and DNA from soldiers’ remains that there may have been several diseases that ravaged the army, including two previously undetected types of bacteria. The study was in the journal Current Biology.
“Previously, we thought there was only one infectious disease that decimated Napoleon’s army — typhus,” said the study’s lead author, Rémi Barbieri, a former postdoctoral fellow at the Pasteur Institute in Paris who currently holds a postdoctoral position at the University of Tartu in Estonia. Instead, investigators discovered something unexpected, opening the door to the possible discovery of other infectious diseases that may have contributed to the soldiers’ deaths, he added.
Researchers found pathogens — Salmonella enterica and Borrelia recurrentis, bacteria that cause paratyphoid fever and relapsing fever, respectively — by analyzing the teeth of dead soldiers found in a mass grave discovered in 2001 in Vilnius, Lithuania.
The new discoveries not only give a clearer picture of a significant historical event, they also highlight how technology has advanced and opened the door to understanding historical circumstances, researchers say.
Cauldron of diseases
When Napoleon and his troops arrived in Moscow, they found no Russian soldiers. Instead, the city was abandoned, with crops burned and no supplies available, including safe food and clean clothing. As the harsh winter months approached, the French army was forced to retreat, but not without facing many difficulties.
Rickettsia prowazekii, the bacteria responsible for typhus, was first detected in the teeth of Napoleon’s soldiers during a 2006 study, but research was limited by technology at the time. To find out whether typhus was solely to blame for the soldiers’ deaths, the authors of the new study used a method known as high-throughput sequencing, which can sequence millions of DNA fragments at once. It allows the identification of highly degraded DNA, such as genome fragments extracted from samples that are more than 200 years old.
“This is something that can only be done with these machines that are very powerful to sequence a large amount of DNA,” said study co-author Nicolás Rascovan, research supervisor and head of the Microbial Paleogenomics Unit at the Pasteur Institute. “This type of analysis, these type of projects, can really give a much clearer picture about the infectious disease landscape in the past… and how (historical events) have also shaped the infectious disease landscape today.”
The study authors analyzed 13 samples and found no traces of typhus, but their work does not discredit the conclusions of the 2006 study, the researchers noted. The study sample is also too small to know the exact impact disease had on Napoleon’s army. “What changes (with) our study is the fact that we now have direct evidence that there were several different infectious diseases present at this site,” Rascovan said. It is likely that more diseases were at play and have not yet been detected, he added.
Cecil Lewis, an ancient DNA researcher who studies the human microbiome, said the results were not particularly surprising, but considered them a significant contribution to “our understanding of the end of Napoleon’s army.” Lewis, academic vice president at the Oklahoma School of Science and Mathematics, did not participate in the study.
“We are now in a period where studies of ancient DNA can contribute more nuance to the understanding of such historical events, which is exciting,” Lewis said in an email. “The study of historical and ancient pathogens, their place in history, offers a glimpse into the evolutionary paths that organisms have taken, some now extinct, others forming the basis of today’s pathogens. This data helps us better understand the possibilities of how pathogens can affect lives, evolve and persist, which is crucial for anticipating and managing future threats.”
Paratyphoid fever and relapsing fever still exist today, but they are not as common or deadly. Napoleon survived the retreat, but his declining army ultimately contributed to his fall from power a few years later.
“Something quite impressive is how, in such a short time, since 2006, with the first study, until today, technologies have developed so much that we can do things that were impossible to imagine a few years ago and are now possible,” said Rascovan. “So I’m really excited to think about what’s next in terms of technological developments.
Image at top: Napoleon Bonaparte in “Portrait of Napoleon I” from 1812, by Charles Auguste Steuben. Photo Josse/Leemage/Corbis/Getty Images
