British squirrels carried leprosy during the Middle Ages, according to a study published in the journal Current Biology. The authors also found a link between the pathogens found in the local population and squirrels during that period.
Symptoms include skin spots, deformed noses, and ulcers. The bacterium responsible for leprosy — called Mycobaterium leprae — still infects 200,000 yearly and has a long history in Europe. A team of researchers from the University of Basel, Switzerland, found that red squirrels (Sciurus vulgaris) were hosts for M. leprae in medieval England. In addition, the leprosy bacteria in medieval squirrels were closely related to those found in human skeletons from the same region.
“This similarity shows us that leprosy bacteria were probably transmitted between animals and humans at that time,” said Professor Verena Schünemann from the University of Basel. However, these results don’t show how this took place. “We don’t know whether the squirrels infected humans or whether humans were the ones to introduce the disease to the animals.” There were many opportunities of contact between humans and squirrels. The most likely was the fur trade, which provided highly popular squirrel fur for noblemen and women in society. Entire coats made from squirrels were common in many royal families. Squirrels were also used as pets and as entertainment in royal courts.
For this study, the team focused on an area in southern England. The samples for the genetic analysis were collected from two different archaeological sites. The human remains were extracted from a medieval leprosarium, a care facility for patients with from leprosy. In addition, the researchers found samples from medieval squirrels thanks to hand and foot bones found at a former skinner’s shop. “We carried out the genetic analyses on the squirrels’ tiny hand and foot bones, which weigh between 20 and 30 milligrams. That is not a lot of material,” explained Christian Urban, first author of the study.
The authors believe this is particularly important in predicting how leprosy is likely to develop in the future. “Our One Health approach prioritises finding out more about the role animals played in the spread of diseases in the past”, said Schünemann. “A direct comparison between ancient animal and human strains enables us to reconstruct potential transmission events over time and helps to form conclusions about the long-term zoonotic potential of the disease.”
Urban C, Blom AA, Avanzi C, Walker-Meikle K, Warren AK, White-Iribhogbe K, Turle R, Marter P, Dawson-Hobbis H, Roffey S, Inskip SA, Schuenemann VJ. Ancient Mycobacterium leprae genome reveals medieval English red squirrels as animal leprosy host. Curr Biol. 2024 May 20;34(10):2221-2230.e8