Red squirrels in the UK carry strains of leprosy similar to those that have afflicted disability and disfigurement on humans for centuries, a study has shown.
Experts stress the chances of catching the disease from a squirrel are extremely low and have urged people living close to the animals not to panic.
Scientists tested DNA samples from 25 red squirrels living on Brownsea Island near Poole and found that every one was infected with the leprosy bacteria Mycobacterium leprae.
The strain was strikingly similar to that recovered from the skeleton of a leprosy victim buried 730 years ago in Winchester.
Other red squirrels from Scotland, Ireland and the Isle of Wight were carrying another kind of leprosy bacteria, Mycobacterium lepromatosis. This strain was closely related to a virulent form of human leprosy endemic in Mexico and the Caribbean.
Brownsea Island in Poole harbour is a red squirrel haven containing a thriving population of about 250 of the endangered rodents.
The new study suggests the island's red squirrels have been affected by leprosy for decades and perhaps centuries.
Not all the infected squirrels were displaying symptoms. Those that did showed signs of swelling and hair loss from the ears, muzzle and feet.
Professor Anna Meredith, from the University of Edinburgh's Royal School of Veterinary Studies, led the Anglo-Swiss team of scientists.
Brownsea Island, owned by the National Trust and Dorset Wildlife Trust, will stay open while the scientists continue their four-year investigation.