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In Medieval England, Leprosy Spread Between Red Squirrels and People, Genome Evidence Shows

Evidence from archaeological sites in the medieval English town of Winchester shows that English red squirrels once served as important hosts for mycobacteria leprosy strains that caused leprosy in people, researchers report May 3 in the journal Current biology.

“With our genetic analysis we were able to identify red squirrels as the first ancient animal host of leprosy,” says lead author Verena Schuenemann, from the University of Basel in Switzerland. “The medieval red squirrel strain we recovered is more closely related to medieval human strains from the same city than to strains isolated from infected modern red squirrels. Overall, our results point to an independent circulation of M. leprae tensions between humans and red squirrels during the Medieval Period.”

“Our findings highlight the importance of involving archaeological material, in particular animal remains, in the study of the long-term zoonotic potential of this disease, since only a direct comparison of ancient human and animal strains allows reconstructions of possible transmission events to over time,” says Sarah Inskip of the University of Leicester, UK, co-author of the study.

Leprosy is one of the oldest recorded diseases in human history and is still prevalent to this day in Asia, Africa and South America. While scientists have traced the evolutionary history of the mycobacteria that causes it, they didn’t know how it may have spread to people from animals in the past, beyond some hints that red squirrels in England may have served as hosts. .

In the new study, researchers studied 25 human and 12 squirrel samples to look for M. leprae at two archaeological sites in Winchester. The city was well known for its leprosarium (a hospital for people with leprosy) and its connections to the fur trade. In the Middle Ages, squirrel skin was widely used to decorate and line garments. Many people also kept squirrels trapped as babies in the wild and raised them as pets.

The researchers sequenced and reconstructed four genomes representing medieval strains of M. leprae, including one of a red squirrel. An analysis to understand their relationships found that they all belonged to a single branch in the M. leprae family tree. They also showed a close relationship between the squirrel strain and a newly constructed one isolated from the remains of a medieval character. They report that the medieval squirrel strain is more closely related to human strains from medieval Winchester than to modern squirrel strains from England, indicating that the infection was circulating among people and animals in the Middle Ages in a way that had not been reported. detected before.

“The history of leprosy is much more complex than previously thought,” Schuenemann said. “The role that animals might have played in the transmission and spread of the disease in the past has not been considered and, as such, our understanding of the history of leprosy is incomplete until these hosts are considered. This finding is relevant “Today such as animal hosts are not yet considered, although they may be important in terms of understanding the contemporary persistence of the disease despite eradication attempts.”

“In the wake of COVID-19, animal hosts are becoming a focus of attention for understanding disease emergence and persistence,” Inskip said. “Our research shows that there is a long history of zoonotic diseases, which have had and continue to have a major impact on us.”