Leprosy affecting UK’s red squirrels
"It was completely unexpected to see that centuries after its elimination from humans in the UK, Mycobacterium leprae causes disease in red squirrels."
An international team of researchers has discovered a medieval strain of leprosy, affecting Britain’s red squirrels on Brownsea Island, just off England’s south coast. The team included vets, researchers and experts from the University of Edinburgh’s Royal (Dick) School of Veterinary Studies, the École Polytechnique Fédérale de Lausanne (EPFL) and the Moredun Institute.
The group tested samples, taken during the post mortems of 25 squirrels from Brownsea, and revealed that all 25 were infected with the Mycobacterium leprae bacteria. Tests also highlighted key similarities between this species of bacteria and a species found in the skeleton of a human leprosy victim, buried over 730 years ago in Winchester, UK. It is possible that the current strain of leprosy, affecting red squirrels on Brownsea, may have been responsible for human epidemics of the disease in medieval Europe.
Studies suggest squirrels on Brownsea Island have been affected by the disease for centuries but that not all squirrels display symptoms. Those that did present with symptoms suffered hair loss on the ears, muzzle and feet.
Scientists have also detected another species of leprosy, affecting red squirrels in other parts of the UK. The research highlights links between this species of leprosy and the DNA found in human cases, in both Mexico and the Caribbean. However, researchers have stressed the improbability of transmitting the disease to humans.
The team’s findings suggest infected red squirrels were reintroduced to Ireland in the early 1800s, via the transfer of animals from England. Presently, researchers are unclear as to whether leprosy poses a major threat to the population of red squirrels. Numbers have declined significantly in the UK, however, this has been attributed to the loss of habitat and the squirrel pox virus, rather than leprosy.
Professor Anna Meredith, of the University of Edinburgh’s Royal (Dick) School of Veterinary Studies, said: “The discovery of leprosy in red squirrels is worrying from a conservation perspective but shouldn’t raise concerns for people in the UK. We need to understand how and why the disease is acquired and transmitted among red squirrels so that we can better manage the disease in this iconic species.”
Professor Stewart Cole, of the École Polytechnique Fédérale de Lausanne, said: “It was completely unexpected to see that centuries after its elimination from humans in the UK, Mycobacterium leprae causes disease in red squirrels. This has never been observed before.”
Although leprosy is no longer a concern for humans in the UK, the disease continues to affect human populations in developing countries. Based on their research, the team (comprised of both vets and human leprosy experts) believes that infected animals harbour the disease, making it impossible to eliminate from these countries. The group will continue to study the disease, in an ongoing, four-year research programme on Brownsea, supported by the National Trust and Dorset Wildlife Trust.
Companies marketing medicines for small pets exempt from authorisation must submit their annual return to the Veterinary Medicines Directorate (VMD) by 30 November 2026.
