The native red squirrels found scurrying around the forests of Britain are harboring a secret. The rodents with a penchant for nuts and pine cones have been found to be carrying multiple strains of the bacteria responsible for leprosy, including one that caused outbreaks of the disease in humans during the medieval period.
The disease, caused by different strains of the bacterium Mycobacterium, was originally detected in red squirrels in Scotland in 2014, but it now appears that the condition is much more prevalent, and that the fluffy critters are actually infected by two different types. Researchers were first alerted to the problem when reports came in that squirrels were spotted with lesions on their ears, snouts, and limbs, with further testing of the endangered animals confirming that they had leprosy.
Additional analysis of 110 dead red squirrels from all across the UK and Ireland found that different populations were being infected by different strains, either Mycobacterium lepromatosis, similar to a human form that is found mainly in Mexico and the Caribbean, and Mycobacterium leprae, the strain that is thought to have been responsible for infecting people in southern England during the Medieval period some 700 years ago. It had been thought to have died out.
Why certain populations have one strain, while others have another is still not understood, but the researchers suggest that it could be affected by sampling, as there are not many of the endangered animals surviving in the UK, meaning they had a fairly small sample size. They are also keen to stress that while it may not be great news for the enchanting creatures, the risk for humans being infected is still very low indeed, with the last recorded case of human leprosy acquired in the UK having been in 1798.
“The discovery of leprosy in red squirrels is worrying from a conservation perspective but shouldn’t raise concerns for people in the UK,” explained Professor Anna Meredith, from the Royal (Dick) School of Veterinary Studies at the University of Edinburgh, and who co-authored this latest study tracking the disease in red squirrels published in Science. “We need to understand how and why the disease is acquired and transmitted among red squirrels so that we can better manage the disease in this iconic species.”
The study raises interesting questions about how the animals may serve as reservoirs for the disease, and how they can persist in the environment even when thought it had long disappeared. While it may be no threat to humans in the UK (despite popular belief, the disease is not highly contagious and required contamination from bodily fluids), it may have implications in other parts of the world where human contact with infected animals is more common.