Napoleon I led an army of around 550,000 soldiers to invade Russia in June 1812, and though they made it to Moscow, they did so without achieving a decisive victory. The army was faced with a destroyed city, so they opted to retreat. Winter camps were constructed along the Polish border that October, and over the next couple of months, this catastrophic retreat ended with the near total loss of the Napoleonic army. Historical records have indicated that cold, starvation, and typhus caused the losses.
Now, scientists have tested this theory by analyzing DNA from thirteen dead soldiers’ teeth, and performing a paleogenomic assessment to determine what microbes lived there. This work did not reveal any evidence of typhus. Instead, the researchers found two other pathogens: traces of Salmonella enterica, a bacterium that can cause enteric fever, and Borrelia recurrentis, which is can be transmitted by body lice and causes relapsing fever.
This work has suggested that relapsing fever and enteric fever could have been major contributors to the demise of that army. The findings have been reported in Current Biology.
Neither Rickettsia prowazekii, which causes typhus; nor Bartonella quintana, which causes trench fever, were found on any of the soldiers that were analyzed. These microbes have, however, been found during a previous research effort at this site, which is in Lithuania and was part of the region where the retreat happened.
The study authors suggested that those previous findings, from 2006, were based on unreliable PCR techniques. These methods can make many copies from a very small bit of starting material. That study analyzed dental pulp from the remains of 35 soldiers, which identified seven soldiers with evidence of B. quintana, and three with R. prowazekii.
"Ancient DNA gets highly degraded into pieces that are too small for PCR to work. Our method is able to cast a wider net and capture a greater range of DNA sources based on these very short ancient sequences," said senior study author author Nicolás Rascovan of the Institut Pasteur in France.
The B. recurrentis strain that was found in this study is part of the same lineage that has been shown to have lived in ancient Britain 2,000 years earlier. This lineage was able to survive for millennia in Europe, but the present-day strains that have been analyzed have, so far, been part of another lineage.
"This shows the power of ancient DNA technology to uncover the history of infectious diseases that we wouldn't be able to reconstruct with modern samples," added Rascovan.
Sources: Cell Press, Current Biology