Multiple diseases may have devastated Napoleon’s army in 1812

By Taylor Nicioli, CNN

(CNN) — Near the end of his reign, French emperor Napoleon Bonaparte led an army of over half a million men in an invasion of Russia in 1812. Six months later, after the army was forced to retreat, an estimated tens of thousands of his soldiers made it back to France.

Known as one of the costliest wars in history, the death of hundreds of thousands of soldiers has been attributed to battle, as well as starvation, cold and a typhus epidemic that broke out.

Now, researchers have found evidence in the DNA remains of the soldiers that there may have been multiple diseases that devastated the army, including two previously undetected types of bacteria. The study was published Friday in the journal Current Biology.

“Previously, we just thought that there was one infectious disease that decimated the Napoleon army — the typhus,” said lead author Rémi Barbieri, a former postdoctoral fellow at the Institut Pasteur in Paris who currently holds a postdoctoral position at Estonia’s University of Tartu. Instead, the researchers found something unexpected, opening the door to potentially uncovering other infectious diseases that could have contributed to the soldiers’ deaths, he added.

The researchers found the pathogens — Salmonella enterica and Borrelia recurrentis, bacteria that cause paratyphoid fever and relapsing fever, respectively — by analyzing teeth from the fallen soldiers who were found in a mass grave uncovered in 2001 in Vilnius, Lithuania.

The new findings not only give a clearer picture of a significant historical event, but they highlight how technology has advanced and opened the door to understanding historical circumstances, researchers say.

Mixing pot of disease

When Napoleon and his troops reached Moscow, they weren’t met with Russian soldiers. Instead, the city was abandoned, with burnt crops and no supplies available, such as safe food to eat or clean clothing. As the harsh winter months approached, the French army was forced to retreat, but not without facing many hardships.

Rickettsia prowazekii, the bacterium responsible for typhus, was first detected in the teeth of Napoleon’s soldiers during a 2006 study, but the research was limited by the technology at that time. To find out if typhus was the sole culprit for the demise of soldiers, the authors of the new study used a method known as high-throughput sequencing, which can sequence millions of DNA fragments at a time. It allows for highly degraded DNA to be identified, such as the genome fragments extracted from samples more than 200 years old.

“This is something that can be only done with these machines that are very powerful to go and sequence a lot of high quantity of DNA,” said study coauthor Nicolás Rascovan, supervisor of the research and head of the Microbial Paleogenomics Unit at the Institut Pasteur. “This sort of analysis, these kinds of projects, can really give a much clearer picture about the landscape of infectious disease in the past … and how (historical events) have also shaped the landscape of infectious diseases today.”

The study authors looked at 13 samples and found no traces of typhus, but their work does not discredit the findings of the 2006 study, the researchers noted. The study sample is also too small to know the exact impact the diseases had on Napoleon’s army. “What changes (with) our study is the fact that now we have direct evidence there were several different infectious diseases present in this site,” Rascovan said. It is likely that more diseases were at play that have yet to be detected, he added.

Cecil Lewis, an ancient DNA researcher who studies the human microbiome, said the results were not particularly surprising, but he called it a meaningful contribution to “our understanding of the demise of Napoleon’s army.” Lewis, vice president of academics at the Oklahoma School of Science and Mathematics, was not involved with the study.

“We are now in a period where ancient DNA studies can contribute more nuance to the understanding of such historic events, which is exciting,” Lewis said in an email. “Studying historical and ancient pathogens, their place in history, offers a glimpse into the evolutionary paths organisms have taken, some now extinct, others forming the foundation of present-day pathogens. These data help us better understand the possibilities for how pathogens can impact lives, evolve and persist, which is crucial for anticipating and managing future threats.”

Paratyphoid fever and relapsing fever are still around today but are not as common or as deadly. Napoleon survived the retreat, but his dwindling army ultimately contributed to his fall from power a few years later.

“Something that is quite impressive is how, in so little time, since 2006 with the first study to today, the technologies have been developed so much that we can do things that were impossible to even conceive a few years ago and now are possible,” Rascovan said. “So I am very excited to think what is going to be next in terms of technological developments.”

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