UK red squirrels are carrying leprosy and have been for decades

Facing yet another threat

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By New Scientist staff and Press Association

A study of 110 dead red squirrels from around the UK and Ireland has found that the animals carry several strains of leprosy.

Red squirrels in Scotland, Ireland and the Isle of Wight were found to be carrying Mycobacterium lepromatosis, a bacterial strain that is closely related to a virulent form of human leprosy endemic in Mexico and the Caribbean. Animals on Brownsea Island in Poole harbour carried a different type, Mycobacterium leprae, which is known to have affected people living in southern England over 700 years ago.

The chances of catching the disease from a squirrel are extremely low, and researchers have urged people living close to the animals not to panic. Instead, the finding is more of a concern for those trying to conserve the animals, which are already threatened by squirrelpox and habitat loss.

“We need to understand how and why the disease is acquired and transmitted among red squirrels so that we can better manage this iconic species,” says Anna Meredith, at the University of Edinburgh.

Human strain

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 can lead to deformity, disability and blindness if left untreated. However, most healthy people are naturally immune to leprosy and are unlikely to be affected if they are exposed to the bacteria.

The strain carried by the Brownsea Island squirrels was particularly surprising, bearing a similarity to a type of leprosy that was previously found in the 730-year-old skeleton of a leprosy victim buried in Winchester, just 43 miles away.

The disease affects the animals’ ears

Dorset Wildlife Trust/PA Wire

The discovery of this medieval leprosy strain in the Brownsea Island so long after it was eliminated from humans was completely unexpected, says team-member Stewart Cole, at the Ecole Polytechnique Federale de Lausanne in Switzerland. “This has never been observed before.”

There are currently around 250 red squirrels on Brownsea Island. Of the 25 dead squirrels the team tested, every one was infected with this leprosy strain.

The last recorded case of indigenous leprosy contracted in the UK dates back to 1798.

Carried for centuries

The team’s findings suggests that the Brownsea squirrels may have been affected by leprosy for centuries.

“Brownsea’s wild red squirrel population has been living with leprosy for at least four decades,” says Angela Cott, National Trust general manager for Brownsea Island. “By working with the University of Edinburgh and Dorset Wildlife Trust, we hope to understand how best to look after Brownsea’s wild red squirrels.”

Fewer than 140,000 red squirrels remain in the UK, and the animals may be extinct in Britain within the next 10 years.

Journal reference: Science, DOI: 10.1126/science.aah3783

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