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Leprosy Left Characteristic Skeletal Lesions in British Red Squirrels

Eurasian red squirrel in Abernethy Forest, Scotland
Research · Disease, parasites & microbiology

Leprosy left characteristic skeletal lesions in three British Eurasian red squirrels (Sciurus vulgaris) infected with Mycobacterium lepromatosis. The study, first published on 10 March 2026, is the first to define a range of skeletal features associated with leprosy in red squirrels.

The researchers examined three adult squirrel skeletons from Scotland that had previously tested positive for M. lepromatosis and had soft-tissue lesions consistent with the disease. Macro- and microscopic examination showed bone destruction, new bone formation, remodelling and increased vascular openings in several parts of the skeleton.

Lesions concentrated in the skull and extremities

The most characteristic changes occurred in the skull, distal limbs and bones of the paws. Two preserved skulls showed destructive lesions and new bone formation in the nasal region. The researchers also found changes in the wrist and ankle bones, metapodials, distal forelimbs and hindlimbs, as well as porous lesions in tail vertebrae.

Many lesions were bilateral, although their severity was not always symmetrical. The authors found that the overall distribution and development of the lesions resembled patterns seen in human leprosy, particularly changes associated with the nose and the ends of the limbs. Leprosy bacteria affect the nervous system; damage to sensory nerves can reduce sensation, promote repeated injury and ulceration, and lead to secondary inflammation of nearby bone. Nerves in cooler distal parts of the body are especially vulnerable, helping explain why the paws and ends of the limbs are characteristic sites of skeletal damage.

The skeletal pattern resembled human leprosy

The authors conclude that the same broad spectrum and anatomical distribution of skeletal lesions known from human leprosy can also develop in red squirrels infected with M. lepromatosis. The resemblance is notable despite the squirrel’s much shorter lifespan and different metabolism.

The study was based on only three infected animals because suitable confirmed specimens are rare. The authors therefore call for additional work on both M. lepromatosis– and M. leprae-infected squirrels to test how consistently the lesion pattern occurs.

Leprosy has been documented in red squirrels in Britain, but its effects had previously been described mainly from soft tissues. The newly identified skeletal pattern gives researchers another way to recognise disease progression in infected animals and may also help identify leprosy in archaeological squirrel remains and other non-human mammals.

Sources and image credit

  1. Elliott, E., Thomas, R., Inskip, S. A., Cooper, A., Kitchener, A. C., Beckmann, K. M., & Meredith, A. (2026). British red squirrels (S. vulgaris) with leprosy develop skeletal lesions. Interdisciplinary Perspectives on Infectious Diseases, 2026, 5785505. https://doi.org/10.1155/ipid/5785505Primary peer-reviewed open-access study first published 10 March 2026. Three adult Scottish red squirrels previously confirmed positive for Mycobacterium lepromatosis were examined macroscopically and microscopically; all showed skeletal lesions consistent with leprosy, particularly in the skull, distal limbs and paws.

Image: Peter Trimming — Eurasian red squirrel (Sciurus vulgaris) in Abernethy Forest, Scotland, photographed 23 April 2014; Wikimedia Commons / Flickr; representative Scottish red squirrel image, not one of the three M. lepromatosis-positive specimens examined in the study · CC BY 2.0 · Source

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