Suspected Frostbite Injuries in Coypu (Myocastor coypus)

SIMPLE SUMMARY: In its indigenous South American habitats, the coypu (Myocastor coypus) is exposed to milder climatic conditions than in most European countries. Owing to the good adaptability of this invasive species, the coypu has spread to regions with other climate zones. After the last severe frost period in February 2021 in Lower Saxony, Germany, several coypus with uncommon skin injuries were harvested. In this period, ground temperatures below −10° Celsius were recorded for approximately two consecutive weeks. The chronological sequence led to the assumption of frostbite injuries. The sampled animals consisted of five female and five male individuals. Post mortem examination revealed ulcerative to necrotizing lesions located predominantly on the tail and/or limbs. The cause of the lesions could not be determined with certainty. However, considering the local weather conditions and the distribution of lesions, frostbite has to be considered as the most likely cause. ABSTRACT: Native to South America, the coypu (Myocastor coypus) is an invasive alien species (IAS) of Union concern. It was introduced to Germany a hundred years ago and is considered established in all German federal states. Between January and February 2021, ground temperatures below −10° Celsius were recorded in Lower Saxony, Germany, for approximately two consecutive weeks. Five male and five female coypus, harvested between 23 February and 31 March 2021, received a post-mortem examination. Nutritional status was poor in six cases, moderate in three and good in one case. Pregnancy was observed in two females. In all the animals, lesions were predominantly found on the distal limbs (n = 7) and/or tail (n = 10), involving the skin and soft tissue with occasional exposure or loss of bones. The histological findings consisted of chronic, ulcerative to necrotizing dermatitis and occasional ulcerative-suppurative dermatitis, necrotizing myositis, thrombosis, granulation tissue, fibrosis and intralesional dystrophic mineralization. Intralesional bacteria were present in six and fungal spores in one animal. Determination of the exact cause was not possible; however, considering the local weather conditions and the distribution of lesions, frostbite injuries have to be considered as the most likely cause. The intralesional bacteria and fungal spores most likely represent secondary contaminants. Interestingly, lesions of this kind have not been reported in coypus in Germany so far. Therefore, frostbite should be considered as a potential cause of disease in coypus, warranting further investigation.