(CN) — The history of leprosy has been rewritten, thanks to a study published Friday in Current Biology. Now, the humble red squirrel plays a major role in the narrative.
“The history of leprosy is far more complex than previously thought,” senior author Verena Schuenemann, from Switzerland's University of Basel, said in a press release. “There has been no consideration of the role that animals might have played in the transmission and spread of the disease in the past, and as such, our understanding of leprosy’s history is incomplete until these hosts are considered."
As one of the earliest diseases identified by humans, leprosy was widely feared, and for a good reason: The disease can cause nerve damage, lesions and severe deformations. Those infected were often confined to leper colonies, or leprosariums, to stop the spread of the disease.
However, researchers have discovered that medieval men and women had more to worry about than infected people. A newly published genetic analysis suggests that the disease was spread by a common rodent.
“With our genetic analysis we were able to identify red squirrels as the first ancient animal host of leprosy,” said Schuenemann.
The researchers analyzed 12th-century human and squirrel bones recovered from around the St. Mary Magdeleine leprosarium in Winchester, UK. Both sets of bones contained evidence of a strain of Mycobacterium leprae, the bacterium that causes leprosy.
"Overall, our results point to an independent circulation of M. leprae strains between humans and red squirrels during the Medieval Period,” said Schuenemann.
In medieval England, there were more than enough opportunities for red squirrels to spread leprosy to humans. This is especially true in Winchester, a city that served as a center for processing and trading the pelts of red squirrels, which were used to trim and line clothing.
These pelts were so highly sought-after that the checkered pattern of a processed form, known as Vair, became a common pattern in medieval heraldry. Red squirrels were also commonly captured and raised as pets.
“Our findings highlight the importance of involving archaeological material, in particular animal remains, into studying the long-term zoonotic potential of this disease, as only a direct comparison of ancient human and animal strains allows reconstructions of potential transmission events across time,” said Sarah Inskip of the University of Leicester, UK, a co-author on the study.
In all, researchers reconstructed the genomes of four medieval-era strains of M. leprae: three from human remains and one from a red squirrel. All four strains were found to be from the same branch of the bacterial family tree.
“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," said Schuenemann.
The researchers contend that this discovery is more than a historic curiosity. They say scientists should consider whether animals are spreading leprosy to humans in the modern day. Leprosy has been discovered recently in armadillos and ticks, both of which could be vectors for the disease.
Their findings can apply to more than just leprosy. For instance, evidence shows that Covid-19 may have originated from racoon dogs.
“In the wake of Covid-19, animal hosts are now becoming a focus of attention for understanding disease appearance and persistence,” Inskip said. “Our research shows that there is a long history of zoonotic diseases, and they have had and continue to have a big impact on us.”
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