A retrospective study (2006-2020) of cytology and biopsy findings in pet rabbits (Oryctolagus cuniculus), ferrets (Mustela putorius furo) and four-toed hedgehogs (Atelerix albiventris) seen at an exotic animal clinic in Tokyo, Japan

Background: Rabbits, ferrets, and four-toed hedgehogs are popular exotic pets, but comprehensive epidemiological studies in these animals have been rarely conducted. The present study aims to clarify the incidence of neoplastic and non-neoplastic diseases in pet rabbits, ferrets and four-toed hedgehogs in Japan. Methods: We histologically/cytologically investigated 1098 samples from 883 rabbits, 812 samples from 521 ferrets and 561 samples from 468 four-toed hedgehogs that were collected at Miwa Exotic Animal Hospital and submitted to the Laboratory of Veterinary Pathology, The University of Tokyo between 2006 and 2020. The examinations of necropsy samples were not included in the present study. Results: Of the 1098 samples from diseased rabbits, 721 (65.7%) were diagnosed as neoplastic and 377 (34.3%) were as non-neoplastic. Uterine adenocarcinoma (21.1%), cutaneous soft tissue sarcoma (15.1%) and mammary gland adenocarcinoma (8.2%) were the most commonly encountered neoplasms. Endometrial hyperplasia (35.8%), testicular atrophy (4.2%) and uterine adenomyosis (3.7%) were the most common non-neoplastic lesions in rabbits. Of the 812 samples from diseased ferrets, 487 (60.0%) were diagnosed as neoplastic and 325 (40.0%) were as non-neoplastic. Adrenocortical tumor (23.2%), lymphoma (19.3%) and pancreatic islet cell tumor (11.5%) were the most commonly encountered neoplasms. Extramedullary hematopoiesis in the spleen (10.5%), lymph node hyperplasia (7.7%) and cholangiohepatitis (4.6%) were the most common non-neoplastic lesions in ferrets. Of the 561 samples from diseased hedgehogs, 338 (60.2%) were diagnosed as neoplastic and 223 (39.8%) were as non-neoplastic. Endometrial stromal tumor and endometrial mixed tumor (23.7%), oral squamous cell carcinoma (13.0%) and cutaneous soft tissue sarcoma (11.5%) were the most commonly encountered neoplasms. Gingivitis/stomatitis (39.5%), endometrial hyperplasia (18.8%) and dermatitis (6.7%) were the most common non-neoplastic lesions in hedgehogs. Conclusions and clinical relevance: Information obtained from the present study will provide a useful reference for veterinarians working with these exotic animals. Based on the literature search, this is the largest-scale retrospective study on disease incidence in hedgehogs.