British Squirrels Carry Leprosy Strain That Plagued Medieval Humans

Leprosy has been detected in British red squirrels, where it causes the same symptoms, such as large sores, found in humans with the disease. Dorset Wildlife Trust

Leprosy, an ancient, disfiguring disease, has been hiding out in Britain, hundreds of years after it was thought to have been eradicated.

A study published November 10 in the journal Science found two types of the bacterium infecting and disfiguring red squirrels in Ireland, Scotland and several isles off the English coast. On one of them, Brownsea Island, researchers discovered a Medieval strain of leprosy nearly identical to that found in a skeleton buried about 730 years ago in Winchester, about 50 miles from Brownsea.

Stewart Cole, director of the Global Health Institute at the Swiss Federal Institute of Technology in Lausanne said the findings suggest the pathogen was transferred from humans to the animals hundreds of years ago.

"It is remarkable that [the bacterium] has persisted for centuries undetected," wrote Roland Brosch of France's Pasteur Institute, in a commentary accompanying the study. The possibility of undiscovered sources of leprosy "existing under our noses must be taken into account for disease control."

Xiang-Yang Han, a physician and researcher at the University of Texas M.D. Anderson Cancer Center in Houston, said he was surprised that the team found the leprosy bacteria in squirrels with and without signs of infection.

"You don't know what animal is carrying the organism, so some may carry the disease without showing it and they could potentially pass it to people," Han said. Cole added that there's a chance this could happen but there's no evidence of it yet.

Leprosy, also known as Hansen's disease, is caused primarily by the bacterium Mycobacterium leprae, though recent work has shown that a closely related bacterium known as Mycobacterium lepromatosis can cause it as well. These bacteria infect the skin, very slowly destroying the skin and associated nerves, leading to terrible disfigurement. It is treatable with antibiotics, though it can take up to a year to resolve.

Brownsea was once an inhabited island with a castle but it is now a nature reserve known for its mostly healthy population of red squirrels. Native to Britain, the squirrels have declined massively since the introduction of eastern grey squirrels from North America, which out-compete them for resources and food.

The researchers found M. leprae in the Brownsea animals, as well as M. lepromatosis infections in animals in Ireland, Scotland and the Isle of Wythe.

Many scholars think the first documentation of a case of leprosy occurred in 1550 B.C., in an Egyptian papyrus document. Leprosy then showed up in Greece in the fourth century B.C. when Alexander the Great's soldiers returned from India, and made their way to Rome in the first century when soldiers came back from Asia Minor.

Over the centuries, the strain of leprosy in Europe changed slightly from those found in India and elsewhere, picking up its own unique genetic signature. That allowed researchers to show that the same type infected the Medieval victim and the modern-day squirrels.

This is only the second animal known to carry leprosy. The first is the nine-banded armadillo, which lives throughout the southern United States. Researchers say It has now been relatively well-established that these creatures can pass the disease through physical contact. But leprosy remains rare in the United States, with an average of 150 new cases per year.

The disease was originally passed from people to armadillos in the last hundred years or so, Cole added. It's the same strain that infected medieval Europeans, and there's no evidence that leprosy existed in the New World prior to a century ago. It leaves recognizable markings on skeletons, Cole said.

Leprosy continues to infect millions around the world, with 220,000 new cases per year—60 percent of them in India.