Red squirrels spread leprosy during the Middle Ages

A study of archaeological sites in Winchester, England, found that red squirrels served as hosts for Mycobacterium leprae strains that caused leprosy in humans.

Leprosy is one of the oldest recorded diseases in human history and still occurs today in Asia, Africa and South America.

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It has previously been suggested that the extensive trade in red squirrel fur, which was highly prized in the Middle Ages, might have contributed to the leprosy epidemic in medieval Europe.

The results of the study, published in the journal Current Biology, examined 25 human and 12 squirrel samples from two medieval sites in Winchester.

During this period, the city had strong ties to the fur trade and housed the leprosarium, a hospital that treated people with Hansen’s disease (leprosy), caused by the Mycobacterium leprae bacteria.

Verena Schuenemann from the University of Basel in Switzerland said: “Our genetic analysis allowed us to identify red squirrels as the first ancient animal hosts of leprosy.”

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The study found that medieval red squirrel strains were more closely related to human strains in Winchester, than to modern squirrel strains from England – indicating an independent circulation of Mycobacterium leprae strains.

“Our findings highlight the importance of including archaeological material, particularly animal remains, when studying the long-term zoonotic potential of this disease, as only a direct comparison of ancient human and animal strains can provide reconstructions of potential transmission events in over time,” said Sarah Inskip from the University of Leicester, UK, co-author of the study.

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Sources: Current Biology, Urban, Blom and Avanzi et al.: “Ancient Mycobacterium leprae genome reveals medieval English red squirrels as hosts for animal leprosy.” https://www.cell.com/current-biology/fulltext/S0960-9822(24)00446-9

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