Abstract

Both pathogenic and commensal amoebae have been documented in a variety of amphibian hosts. Various species in the genus Entamoeba are recognized as a cause of dysenteric disease across several taxa.^1,2 Clinical entamoebiasis in amphibians, however, is uncommonly reported, and most descriptions are limited to disease in individuals or a few animals.^3,4,5,6,7,8 This report details a case of amoebiasis that resulted in mortality in a population of Cranwell’s horned frogs (Ceratophrys cranwelli).

Regurgitation was observed in a captive private population of approximately 1000, 4-week-old albino C. cranwelli, which was followed one week later by a spike in mortalities (nearly 150 deaths over a 3-day span). Seventeen, live, moribund frogs were submitted for post-mortem examination that included cytologic, bacteriologic, parasitologic, and histopathologic assessment. No bacterial growth was observed on brain or kidney cultures completed on 4 individuals. On cytologic examination, intestinal contents of a subset of frogs contained a large population of opalinid heterokonts and spironucleoid-like flagellates as well as a mixed population of bacteria. Blood smears from 3 animals were consistent with chronic-active systemic inflammation. Histopathologic evaluation of 6 frogs identified severe necroulcerative colitis associated with numerous intracytoplasmic amoebic trophozoites in mucosal enterocytes, and variable involvement of the small intestine. Zinc-polyvinyl alcohol fixed and trichrome stained scrapes of colonic mucosa identified amoebic trophozoites with morphology most consistent with an Entamoeba species. Further molecular and ultrastructural characterization is pending. Treatment with daily 8-hour 25 mg/gal metronidazole baths was recommended for the remaining collection and a subsequent reduction in mortalities was reported.

* Presenting author, + Student presenter

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