# British Red Squirrels (S. vulgaris) With Leprosy Develop Skeletal Lesions

## TL;DR

Red squirrels with leprosy show skeletal changes similar to those in humans, indicating the disease affects their bones.

## Contribution

First evidence of leprosy-induced skeletal lesions in red squirrel skeletons.

## Key findings

- Erosive lesions and bone remodeling were found in multiple skeletal regions of infected squirrels.
- Porosity in the caudal vertebrae and nasal bones was observed in leprosy-positive specimens.
- Skeletal changes in squirrels with leprosy resemble those seen in human leprosy cases.

## Abstract

Leprosy, caused by Mycobacterium lepromatosis or Mycobacterium leprae, has been reported in red squirrels in Britain from Scotland to the south of England. However, there has been no attempt to determine whether lesions caused by leprosy can be detected in the skeletons of infected animals. Here, we present findings from three red squirrel skeletons (Sciurus vulgaris L., 1758) that had soft tissue lesions consistent with leprosy and were positive for M. lepromatosis. Three of six red squirrel specimens from Scotland that previously tested positive for M. lepromatosis were subjected to macro‐ and microscopic skeletal analyses. Erosive lesions, remodelling and porosity were found in multiple parts of the skeleton, including the podials, tarsals, distal tibiae, distal forelimbs and in the nasal bones. Additionally, porous lesions were found in the caudal vertebrae. These skeletal changes advance our knowledge of how this disease manifests in nonhuman mammals. Overall, these findings demonstrate that, despite the squirrel’s significantly shorter lifespan and different metabolism, comparable patterns of skeletal lesions are observed in humans and red squirrels with leprosy.