Colorectal basidiobolomycosis in a dog

Abstract

A 7-year-old castrated male French Bulldog was examined for chronic large intestinal enteropathy. A colonic mass and thickened rectal mucosa were identified, and histopathologic examination of endoscopic biopsy specimens disclosed eosinophilic proctitis with large (5-20 μm), irregularly shaped, pauciseptate hyphae that were Gomori methenamine silver and periodic acid-Schiff positive. Amplification and sequencing of ribosomal DNA extracted from paraffin-embedded tissues yielded a sequence with 97% identity to GenBank sequences for Basidiobolus ranarum. After itraconazole, terbinafine, and prednisone administration, clinical signs resolved rapidly, and sonographic lesions were largely absent after 6 weeks. Treatment was discontinued by the owner 15 weeks after diagnosis. Three weeks later, the dog collapsed acutely and was euthanized. Necropsy identified metastatic islet cell carcinoma and grossly unremarkable colorectal tissues. However, histopathology of the rectum disclosed multifocal submucosal granulomas with intralesional hyphae morphologically similar to those previously observed. This report is the first to describe medical treatment of gastrointestinal basidiobolomycosis in a dog.

Keywords: Basidiobolus ranarum; entomophthoromycosis; itraconazole; pythiosis; zygomycosis.

FIGURE 1

Photomicrograph of an endoscopically obtained rectal pinch biopsy specimen showing mixed eosinophilic proctitis with large, irregularly shaped hyphae (black arrows) with thin, nonparallel walls and rare septae. The hyphae are surrounded by a thin sleeve of eosinophilic material (white arrowhead). Hematoxylin and eosin stain; scale bar = 50 μm

FIGURE 2

Photomicrograph of rectal tissue taken at necropsy showing multifocal to coalescing granulomas (arrows) in the submucosa (A); hematoxylin and eosin stain; scale bar = 500 μm. Large, thin‐walled, irregularly shaped hyphae (arrows) within granulomas were GMS (B) and PAS (C) positive; scale bar = 20 μm