First skeletal evidence of leprosy in British red squirrels

A University of Leicester-led study [1] has identified the first known skeletal evidence of leprosy in British red squirrels, offering new insights into how the disease affects wildlife and how it may be detected in both modern and archaeological remains.

Leprosy is a chronic infectious disease that damages the skin, nerves and mucous membranes, leading in humans to symptoms such as skin lesions, numbness, muscle weakness and, in severe cases, paralysis. Although now relatively rare in many regions, there were 182,815 new human cases reported globally in 2023.

While leprosy has previously been detected in red squirrels through soft-tissue analysis and molecular methods, this is the first study to demonstrate its impact on the skeleton in a non-primate mammal. Researchers examined three infected red squirrels from Scotland, all confirmed to carry Mycobacterium lepromatosis.

The animals showed distinctive skeletal changes, including cranial porosity, bone loss and remodelling, alongside damage to limbs and paws consistent with neuropathy and secondary infection. The findings indicate that red squirrels develop bone changes closely resembling those seen in human cases of leprosy.

The study also confirms that Mycobacterium lepromatosis produces skeletal effects similar to those caused by Mycobacterium leprae, the better-known leprosy pathogen.

Lead researcher Elliot Elliott, a PhD researcher in Leicester’s School of Heritage and Culture, said: “Our research establishes the first comprehensive skeletal diagnostic criteria for leprosy in non-human mammals and provides a framework for identifying the disease in wildlife and archaeological remains.”

He added that further investigation into additional rodent hosts and disease progression could help improve understanding of leprosy transmission and potentially inform future human treatments.

The work builds on earlier University of Leicester research showing that medieval red squirrels in England may have acted as hosts for Mycobacterium leprae strains associated with human leprosy, highlighting a longer and more complex historical relationship between wildlife and the disease.

More information online

1. British Red Squirrels (S. vulgaris) With Leprosy Develop Skeletal Lesions published in Interdisciplinary Perspectives on Infectious Diseases