Genomic evidence reveals the spread of leprosy between red squirrels and humans in medieval England

Archaeological evidence from medieval English sites in Winchester suggests that red squirrels served as hosts for strains of Mycobacterium leprae that caused leprosy in humans. Researchers from the University of Basel in Switzerland conducted genetic analyzes on ancient animal remains and found that medieval red squirrels were the first known animal hosts of leprosy. The research also found that the medieval strain found in red squirrels was closely related to human strains from the same town, indicating independent circulation of the disease between humans and squirrels during the Middle Ages.

The importance of including archaeological material, such as animal remains, when studying the long-term zoonotic potential of diseases such as leprosy was highlighted by the researchers. By comparing ancient human and animal strains, they were able to reconstruct potential transmission events over time. Leprosy, one of the oldest recorded diseases in human history, is still common in parts of Asia, Africa and South America. Understanding how the disease spread from animals to humans in the past is crucial to our knowledge of its evolutionary history.

The researchers studied 25 human and 12 squirrel samples at two archaeological sites in Winchester, a city known for its leprosarium and connections to the fur trade. Squirrel fur was widely used in the Middle Ages to decorate and line garments, and many people kept squirrels as pets. By sequencing and reconstructing four genomes representing medieval strains of M. leprae, including one from a red squirrel, the researchers were able to demonstrate a close relationship between the squirrel strain and a human strain from medieval Winchester. This suggests that the infection circulated between humans and animals during the Middle Ages.

The discovery of a medieval strain of M. leprae in red squirrels adds a new layer of complexity to our understanding of the history of leprosy. The role of animals in the transmission and spread of the disease has not been properly considered in the past, leading to an incomplete understanding of the history of leprosy. The researchers believe this finding is relevant today because animal hosts are still not widely considered in the study of diseases such as leprosy, despite their potential significance for understanding the disease’s persistence over time .

In the context of the COVID-19 pandemic, the researchers point out that animal hosts are now becoming a focus for understanding the appearance and persistence of diseases. The long history of zoonotic diseases, as evidenced by the findings of this study, highlights the significant impact that animals can have on human health. By studying the historical transmission of diseases such as leprosy between humans and animals, we can gain valuable insights into how these diseases have developed and persisted, even despite efforts at eradication.