Did Leprosy in the UK Spread from Squirrels to Humans, or Was It the Other Way Around?

Written by Camilla Jessen

May.08 - 2024 2:00 PM CET

Photo: Wikimedia Commons
Photo: Wikimedia Commons
In England, leprosy jumped from squirrels to humans in the Middle Ages. Or was it the other way around?

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A recent study conducted by researchers from the University of Leicester has revealed fascinating insights into the transmission of leprosy in medieval England, suggesting that red squirrels played a role in spreading the disease among humans.

The findings, published in the journal Current Biology, support the longstanding theory that the fur trade, particularly involving squirrel pelts from Viking Scandinavia, might have facilitated the spread of leprosy.

Leprosy, caused by the bacterium Mycobacterium leprae, has afflicted humanity for millennia, with documented cases causing severe disfigurement across various societies.

While modern instances of the disease are largely confined to Southeast Asia and readily treatable with antibiotics, leprosy was a common and feared illness in medieval England.

Evidence from Winchester: A Key Trading Hub

The connection between humans and red squirrels concerning leprosy was first suggested by previous genetic studies, which showed a close relation between the leprosy strains in medieval human populations in England, Denmark, and Sweden, and those found in present-day red squirrels in the southern UK.

The new study adds a layer of detail to this hypothesis by analyzing DNA from human and squirrel remains found in Winchester—a major medieval city known for its leper hospital and fur trade.

Dr. Sarah Inskip, who co-authored the study, expressed excitement about the discovery, stating, "This is the first time that we found an animal host of leprosy in the archaeological record, which is really exciting."

The research team examined samples from three individuals who lived between 900 and 600 years ago and a squirrel from approximately 1,000 to 900 years ago, uncovering remarkably similar strains of leprosy in both humans and the animal.

What This Means Today

The analysis suggests a possible two-way transmission of the disease between humans and squirrels.

Although the study could not definitively conclude whether humans contracted leprosy from the squirrels or vice versa, the implication is that the interaction between the species, possibly through the fur trade or as pets, facilitated the spread.

In 1384 alone, records show that 377,200 squirrel skins were imported into England, highlighting the scale at which these animals were traded and potentially increasing the disease's transmission rates.

The study not only sheds light on historical disease dynamics but also suggests implications for current leprosy research.

Dr. Inskip recommended investigating animals in current endemic areas to understand better why leprosy persists in certain populations today.

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