Intestinal entamoebiasis in a captive colony of Anderson’s crocodile newts Echinotriton andersoni

Entamoeba protozoa are known to cause enteric and sometimes systemic disease in both domestic and non-domestic animals. In amphibians, Entamoeba spp. are primarily documented as incidental gastrointestinal inhabitants, with rare reports of clinically significant entamoebiasis. In the last decade, mortality outbreaks caused by a recently described protozoan, Entamoeba sp. CT1, have been documented in free-ranging anurans in Australia and managed anurans in the USA associated with gastroenteritis and substantial morbidity and mortality. In 2023, a small population of Anderson's crocodile newts Echinotriton andersoni in managed care at a zoological institution experienced a disease outbreak resulting in the death or euthanasia of 4/13 (31%) newts over an approximately 1 mo period. Clinical signs included dehydration, poor skin quality, and lethargy. Postmortem examination of 3 newts revealed marked, proliferative, and necrotizing inflammation of the intestinal tract, urinary bladder, and cloaca with intramucosal amoebic protozoa. The gonadal ducts (2/3 newts) were also variably affected. Entamoeba PCR and Sanger sequencing of formalin-fixed paraffin-embedded intestinal tissue from all examined newts amplified DNA with 100% sequence identity to the recently identified Entamoeba sp. CT1. However, unlike reports of Entamoeba sp. CT1 in anurans, lesions in the crocodile newts were not restricted to the gastrointestinal tract. This is the first report of Entamoeba sp. CT1 causing significant clinical disease in caudates, emphasizing its importance as an amphibian pathogen with the potential to cause disease in managed and free-ranging amphibian populations.