Red squirrels may have brought leprosy to Britain more than 1,000 years ago, new research suggests.
DNA taken from a fifth-century victim of the disease in Essex revealed the same strain of leprosy bacteria carried by red squirrels today.
The discovery supports the theory that the fluffy rodents, once prized for their meat and fur, played a role in the spread of leprosy throughout medieval Europe.
Scientists took samples of leprosy DNA from 90 European individuals with skeletal deformations characteristic of the disease spanning the period 400 AD to 1,400 AD.
From the fragments they reconstructed 10 new genomes – complete genetic codes – of medieval Mycobacterium leprae, the bug that causes leprosy.
One was from Great Chesterford, Essex, and dated to between 415-545 AD. It was this leprosy genome, the oldest yet constructed, that contained the red squirrel clue.
Grey squirrels were not introduced to the UK until the 19th century.
Lead researcher Dr Verena Schuenemann, from the University of Zurich, Switzerland, said: “The dynamics of M. leprae transmission throughout human history are not fully resolved.
“Characterisation and geographic association of the most ancestral strains are crucial for deciphering leprosy’s exact origin.
“While we have some written records of leprosy cases that predate the Common Era, none of these have yet been confirmed on a molecular level.”
The new research, published in the journal Public Library of Science Pathogens, suggests that leprosy may have originated in western Europe or Asia.
Leprosy was prevalent in Europe until the 16th century and is still endemic in many countries, with more than 200,000 cases reported each year.
The medieval genomes included strains now found in Asia, Africa and the Americas.
Senior author Dr Johannes Krause, director of the Max Planck Institute for the Science of Human History in Germany, said: “We found much more genetic diversity in ancient Europe than expected.
“Additionally, we found that all known strains of leprosy are present in Medieval Europe, suggesting that leprosy may already have been widespread throughout Asia and Europe in antiquity or that it might have originated in western Eurasia.”