Research has revealed that medieval red squirrels in England carried bacteria responsible for leprosy, shedding light on disease transmission between humans and animals throughout history.
In a study published in the journal Current Biology, archaeologists uncovered evidence from archaeological sites in Winchester, England, indicating that red squirrels were hosts for strains of Mycobacterium leprae, the bacteria that causes leprosy in humans, during medieval times.
Lead author Verena Schuenemann of the University of Basel in Switzerland explains, “Through genetic analysis, we identified red squirrels as the first known ancient animal host of leprosy. The strain of leprosy found in medieval red squirrels is more closely related to strains found in medieval humans from the same city than to modern strains found in infected red squirrels today. This suggests independent circulation of the bacteria between humans and red squirrels during the Middle Ages.”
Co-author Sarah Inskip from the University of Leicester emphasizes the importance of incorporating archaeological evidence, particularly animal remains, into studies of disease transmission over time. “Only by comparing ancient human and animal strains can we reconstruct potential transmission events across different time periods,” she says.
Leprosy, one of the oldest recorded diseases in human history, is still prevalent in parts of Asia, Africa, and South America. While the evolutionary history of the bacteria that causes leprosy has been traced, how it spread from animals to humans in the past has remained unclear, despite indications that red squirrels in England may have been involved.
In the study, researchers analyzed samples from 25 humans and 12 squirrels from archaeological sites in Winchester, a city known for its leprosarium and connections to the fur trade. The analysis revealed four genomes of medieval strains of M. leprae, including one from a red squirrel. All these strains belonged to a single branch on the M. leprae family tree, indicating close relationships among them. Notably, the strain found in squirrels showed a close relationship with strains isolated from medieval humans, suggesting ongoing transmission between people and animals during the Middle Ages.
“This discovery challenges our previous understanding of leprosy’s history,” says Schuenemann. “Until now, the role of animals in the transmission and spread of the disease has been overlooked, leaving gaps in our knowledge. Considering animal hosts is essential for a comprehensive understanding of leprosy’s history and its persistence over time, even in contemporary times despite efforts to eradicate it.”
“In light of the COVID-19 pandemic, there is growing interest in understanding disease emergence and persistence, with a focus on animal hosts,” adds Inskip. “Our research underscores the long history of zoonotic diseases and their significant impact on human health.”
The study, titled “Ancient Mycobacterium leprae genome reveals medieval English red squirrels as animal leprosy host,” was published on May 3, 2024, in Current Biology.
