Story highlights Researchers believe new strains of leprosy are linked to strains from 27,000 years ago

A person exposed to leprosy may not develop symptoms for 20 years

(CNN) Leprosy was thought to have been eradicated from the UK for centuries -- until now. It turns out the disease has been harbored, perhaps since the Middle Ages, in red squirrels in the British Isles. And research indicates that these squirrels could transmit the disease to humans, though the chances are low.

Red squirrels are endangered in the UK, and researchers were analyzing what they could do to help save the population.

According to a study recently published in the journal Science , researchers discovered the leprosy outbreak after recent sightings of squirrels in Scotland that exhibited symptoms such as skin lesions. They then analyzed squirrel cadavers from Great Britain, Ireland and Scotland and found that they were infected with Mycobacterium lepromatosis or Mycobacterium leprae.

Several squirrels in Ireland, Scotland and the Isle of Wight were infected with a strain of M. lepromatosis. That strain was discovered in 2008 and was previously thought to infect only humans in the Caribbean and Mexico. These strains probably developed from a common ancestor about 27,000 years ago, according to the study.

M. leprae was found in red squirrels specifically from Brownsea Island, England. And it is most similar to the strain that plagued humans in medieval England and Denmark. It closely matches a strain found in the skeletal remains of a leprosy victim buried about 730 years ago near the island.

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