Red squirrels! Adorable, right? Wrong – they're riddled with leprosy

Blighty's dwindling population of red squirrels is riddled with leprosy, according to new research.

Not full-on leprosy, but leprosy-lite, according to a paper with the Ronseal title of Leprosy in Red Squirrels, published in Science, alongside a report titled Red squirrels in the British Isles are infected with leprosy bacilli.

While studying populations of the endangered critters, which are facing habitat destruction and competition from their grey North American cousins, boffins found that some in Scotland had begun to spout strange growths from their extremities.

This was discovered to be Mycobacterium lepromatosis, a newly discovered form of leprosy which can infect humans but is not the classical cause of the disease.

After reporting the wart-like growths, the researchers received alerts from the public about other strange squirrel sightings across the UK, and the University of Edinburgh's Professor Anna Meredith checked out reports from the isolated Brownsea Island in Dorset, where red squirrels were discovered to be infected with the classical form of the disease.

With so much leprosy going around, the researchers conducted a full-on study using genomics, histopathology, and serology, and found that the newer leprosy was infecting squirrels from England, Ireland, and Scotland, and the classic leprosy bacteria in squirrels from Brownsea Island.

Comparison between the newer squirrel leprosy and two strains of human leprosy from Mexico show that the bacteria diverged from a common ancestor around 27,000 years ago, whereas the Brownsea Island strain is much closer to one that circulated in medieval England.

Red squirrels are thus a reservoir for leprosy in the British Isles, the researchers propose, but it is not clear whether they were responsible for spreading the disease, or if they had caught it themselves from humans. ®