Adenomatous hyperplasia of the mucous glands in captive Archey’s frogs (Leiopelma archeyi)

Abstract

AIMS: To describe the gross and light microscopic characteristics of skin lesions observed on the ventral skin of captive Archey’s frogs (Leiopelma archeyi) between 2000 and 2012, and to investigate their occurrence, possible aetiology and association with survival.

METHODS: Postmortem skin samples were obtained for histological evaluation from 37 frogs, with and without skin lesions, that died while in captivity at Auckland Zoo between 2000 and 2012. Four frogs with skin lesions were biopsied under general anaesthesia and samples used for both light and transmission electron microscopy. The records of 94 frogs held at the University of Otago and Auckland Zoo between 2000–2012 were reviewed, which included some frogs recently collected from the wild. Information about the occurrence of skin lesions, and mortality associated with skin lesions was collated.

RESULTS: Grossly the skin lesions varied in appearance; most were circular, pale grey papules, which measured from <0.5–1.5 mm in diameter with no umbilication. The overlying epidermis was not fragile and there was no associated inflammation. Contents often appeared clear or semi-transparent. Lesions were located predominantly on ventral surfaces including trunk, thighs, lower legs and forearms, and gular region, but not on digits. The number ranged from single to multiple, often confluent lesions covering the entire ventral surface of the frog. Histologically the lesions consisted of enlarged proliferating mucous glands that expanded the dermis and elevated the epidermis. They were semi-organised, solid or occasionally cavitated acinar structures with central lumina which sometimes contained mucus. Nuclei showed moderate anisokaryosis and mitotic figures were uncommon. Transmission electron microscopy did not show any infectious agents. Between 2000 and 2012, skin lesions were recorded in 35/94 (37%) frogs. The size and location of skin lesions varied over time, with some resolving and sometimes reappearing. Skin lesions were not associated with an increased risk of death.

CONCLUSIONS: The skin lesions had the gross and microscopic characteristics of adenomatous hyperplasia of the dermal mucous glands.

CLINICAL RELEVANCE: The aetiology of this adenomatous hyperplasia is unknown, but factors associated with the captive environment are the most likely cause. This is the first description of adenomatous hyperplasia of the cutaneous mucous glands in amphibians.

KEY WORDS:

• Adenomatous hyperplasia
• Archey’s frog
• amphibian
• Leiopelma archeyi
• mucous gland

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Corrigendum

Acknowledgments

The authors thank the following people for their technical assistance: Lee Skerratt from James Cook University; Giovanni Delfino from the University of Florence; Melanie Farrant, Richard Jakob-Hoff and John Potter of the New Zealand Centre for Conservation Medicine; Brett Gartrell, Kerri Morgan and Richard Norman from Massey University IVABS; Matthew Downing and Sabine Melzer of the University of Otago; and Hilary Holloway from the University of Auckland. The authors also thank Bruce Waldman for his foundational work with New Zealand native frogs. Finally, the authors acknowledge the Maori iwi for their continued support of native frog research and conservation.

Additional information

Funding

Funding for transmission electron microscopy and histology was supplied in-kind by James Cook University, the New Zealand Centre for Conservation Medicine, the New Zealand Department of Conservation, the University of Auckland and the University of Otago.