13 May 2018 - bbc.com
The discovery supports the theory that the rodents, may have spread of the disease throughout medieval Europe
Red squirrels may have brought leprosy to Britain more than 1,000 years ago, scientists have said.
Swiss researchers said DNA taken from a fifth-century victim of the disease in Essex revealed the same strain of leprosy carried by red squirrels today.
The discovery supports the theory that the rodents, once prized for their meat and fur, played a role in the spread of the disease throughout medieval Europe.
Grey squirrels were not introduced to the UK until the 19th Century.
Scientists at the University of Zurich took samples of leprosy DNA from 90 Europeans with skeletal deformations characteristic of the disease from AD400 to AD1,400.
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 AD415 and AD545. It was this leprosy genome, the oldest yet constructed, that contained the red squirrel clue.
'Not fully resolved'
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.
Lead researcher Dr Verena Schuenemann said: "The dynamics of Mycobacterium 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.
The medieval genomes included strains now found in Asia, Africa and the Americas.