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.
The project aimed to find out how the disease affects and is passed between the red squirrels and how conservationists can control its spread.
But the experts have said 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, Dorset, 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 – just 43 miles (69km) away.
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.
In humans, leprosy causes nerve and muscle damage which left untreated can lead to deformity, disability and blindness.
The scientists have played down the risk to humans, pointing out that the vast majority of healthy people are naturally immune to leprosy and will not be affected even if exposed to the bacteria.
Despite popular myths about leprosy leaping from person to person through physical contact, the infection is not highly contagious.
It is believed to be spread chiefly by coughing or sneezing.
‘The discovery of leprosy in red squirrels is worrying from a conservation perspective but shouldn’t raise concerns for people in the UK,’ said Professor Anna Meredith, from the University of Edinburgh’s Royal School of Veterinary Studies, who led the team.