Researchers investigating the cause of mysterious sores detected on Red Squirrels in the UK and Ireland found something disturbing - the rodents were infected with the bacterium Mycobacterium leprae, which causes leprosy in humans.

The researchers conducted genetic screening and blood tests on more than 100 red-squirrel cadavers from England, Ireland and Scotland.  A quarter of these animals had skin lesions along with swelling of their snouts, ears, lips, eyelids and extremities - which are some of the symptoms also seen in people with the disease.  They all had been collected from the UK's Brownsea Island, and they were infected with the bacterium Mycobacterium leprae, which is the oldest pathogen associated with leprosy and was responsible for outbreaks of the disease in medieval Europe.  A few tested positive for a related bacterium, Mycobacterium lepromatosis, which can also cause leprosy.

It suggests that leprosy hasn't been eradicated from the British Isles, as was the conventional wisdom.  It can exist in the human body for years, eventually leading to skin lesions, eyesight problems, and nerve decay.  A patient who loses the ability to feel pain might repeatedly damage parts of their body (something that led to the myth that leprosy causes limbs to drop off).  It's easily cured in the modern era with steroids and antibiotics, especially when caught early.

"The main message of this is that the number of non-human reservoirs of leprosy might be much higher than previously thought," said Charlotte Avanzi of the Swiss Federal Institute of Technology in Lausanne.  "This is of particular interest in countries where leprosy is still endemic in humans, where maybe a part of the new cases number could be explained by the presence of an animal reservoir."