Leprosy May Have Spread Between Humans and Squirrels in Medieval England, Genome Analysis Shows

Leprosy remains prevalent in South America, Africa, and Asia, with more than 200,000 cases every year. While the evolutionary history of this disease is explained by understanding the nature of its causative agent, the role played by animal hosts remains unexplored.

(Photo: Wikimedia Commons/ Michael Hurst)

Interspecies Transmission of Leprosy

In a recent study, evidence from the medieval city of Winchester shows that English red squirrels may have served as an important host for bacterial strains that cause human leprosy. The study's results were described in the paper "Ancient Mycobacterium leprae genome reveals medieval English red squirrels as animal leprosy host."

Led by Verena Schuenemann from the University of Basel in Switzerland, the research team investigated 25 human and 12 squirrel samples at two archaeological sites in Winchester. The city was famous for its leprosarium and its connections to the fur trade. During the Middle Ages, squirrel fur became famous because it was used to trim and line clothing. Many people also kept wild squirrels as pets.

Schuenemann and colleagues analyzed four genomes representing medieval strains of Mycobacterium leprae, including one from a red squirrel. Genomic analysis discovered that they all belonged to a single Mycobacterium leprae family tree branch. They also indicated a close connection between the squirrel strain and a newly constructed one isolated from the remnants of a medieval person.

The genetic analysis allowed the researchers to identify red squirrels as the first ancient animal host of one of the oldest recorded diseases in human history. The bacterial strains they obtained are more closely linked to medieval human strains from Winchester than those isolated from infected modern species. Generally, their findings point to an independent transmission of strains of Mycobacterium leprae between red squirrels and humans during the Medieval Period.

According to research co-author Sarah Inskip from the University of Leicester in the UK, their study highlights the importance of involving animal remains in studying the long-term zoonotic potential of leprosy. This is because reconstructions of transmission events across time can only be achieved through a direct comparison of ancient human and animal strains.

What is Leprosy?

Leprosy is a chronic infectious disease affecting a person's eyes, skin, mucosal surfaces of the upper respiratory tract, and peripheral nerves. Also known as Hansen's disease, it is caused by a type of bacteria called Mycobacterium leprae.

Leprosy can be transmitted through droplets from the nose and mouth, but prolonged contact for months with a person with untreated leprosy is needed to catch the disease. It is not easily spread through casual contact, such as hugging, shaking hands, sitting beside each other, or sharing meals.

The history of this disease is far more complex than previously thought. In the past, the role played by animals in the transmission and spread of leprosy during ancient times has not been considered. Because of this, understanding the history of this bacterial infection is not complete until the animal hosts are considered.