Recently discovered DNA fragments of relapsing fever pathogens present in the remains of soldiers killed in Napoleon's retreating army in the Russian Empire belong to a very ancient variant of this disease that was widespread in Europe more than 2,000 years ago and is no longer found, according to European paleogeneticists.
The scientists' findings are published in the journal Current Biology.
„Our phylogenetic analysis shows that the Borrelia strain that caused relapsing fever in Napoleon's army was remarkably similar in its DNA structure to bacteria that affected the inhabitants of England during the Iron Age. This suggests that this variant of the infection circulated in Europe for at least two millennia, but was subsequently replaced by modern strains of these microbes,“ the study says.
This conclusion was reached by a team of scientists led by Nicolas Rascovan, head of the paleogenomics department at the Institut Pasteur“ (France) while studying the remains of 13 soldiers from Napoleon's army buried in December 1812 in Vilnius and exhumed in 2002. Previously, researchers had found possible traces of typhus and trench fever, as well as their vectors, in these remains, but they had not yet been studied using modern paleogenetic methods.
Recently, scientists have filled this gap and found that fragments of DNA from the pathogen of paratyphoid fever (Salmonella enterica) were present in the bodies of four deceased French soldiers, and fragments of the genome of Borrelia recurrentis, the bacterium that causes relapsing fever, were found in the bones of two more soldiers. Previously, scientists had not suspected that both diseases were common in Napoleon's army, which makes these findings particularly interesting.
Guided by these considerations, paleogeneticists compared the DNA structure of the “Napoleonic“ Borrelia recurrentis with the genomes of other ancient variants of relapsing fever. This analysis unexpectedly revealed that the soldiers of Napoleon's retreating army were infected with a very ancient form of this disease, analogues of which were common about 2,000 years ago in Iron Age England and other regions of Northern Europe.
The scientists note that these variants of relapsing fever were not very deadly in themselves, but in combination with chronic exhaustion, colds and other diseases, including paratyphoid, they could take a large number of lives among French soldiers. This serves as additional evidence that a significant part of the former “Grand Army“ Napoleon's army died of disease in the winter of 1812, the scientists concluded.
Napoleon's so-called Grand Army consisted of an estimated 500,000-600,000 soldiers from across Europe, with the French making up roughly half of the force. In June 1812, it invaded the Russian Empire and was almost completely destroyed by December 1812, losing an estimated 300,000 men during the retreat alone due to cold temperatures, food shortages and infections.