Squirrels were carriers of leprosy in the Middle Ages.

Data collected from medieval archaeological sites in the English city of Winchester show that red squirrels once served as a breeding ground for strains Microbacterium leprosy causing leprosy among the townspeople, researchers write in Current Biology.

“Thanks to our genetic analysis, we were able to determine that red squirrels were the first animal host of leprosy,” says study lead author Verena Schünemann of the University of Basel in Switzerland.

“The medieval red squirrel-related strain we found is more closely related to human strains present in the same city than to modern red squirrel strains. Ultimately, our results show independent circulation M. leprosy between humans and red squirrels during the medieval period. »

Leprosy is one of the oldest diseases in human history and is still present today, especially in Asia, Africa and South America. Although researchers have traced the evolutionary history of the mycobacterium that causes it, we still do not know how the disease was transmitted from animals to humans in the past, except for a few indications that Red Squirrel Disease in the United States Kingdom may have served as a host.

As part of the study, scientists examined 25 human and 12 squirrel samples in an attempt to detect traces of M. leprosy, at two archaeological sites in Winchester. During the Middle Ages, the city was well known for its leper hospitals, as well as its connections with other suppliers and fur traders.

Moreover, at that time, squirrel hair was often used in clothing. Several residents also have squirrels after trapping wild animals.

After sequencing and reconstructing four genomes representing as many medieval strains M. leprosy, including one that originated from the red squirrel. Further analysis revealed that not only were all of these strains related, but the one associated with the squirrel was the same one that was also found in the remains of a local resident at the time.

The researchers also say that the red squirrel strain in the Middle Ages was more closely related to the strain found in people living in Winchester during this period of history than the strains found in British squirrels today. This, as written, indicates that the infection circulated between animals and humans in the Middle Ages in a way that had not yet been discovered.

“The history of leprosy is much more complex than we thought,” Ms. Schünemann stressed. “We have not considered the role that animals may have played in disease transmission in the past, and so our understanding of the history of leprosy will be incomplete until we consider the description of these hosts. »

“In the wake of COVID-19, animal hosts are gaining attention when it comes to understanding the emergence and persistence of disease,” said Sarah Inskeep, co-author of the University of Leicester study.

“Our research shows that zoonotic diseases have a long history and that they have had and continue to have a major impact on us. »