Abstract

Three captive-bred, individually housed adult tiger salamanders (Ambystoma tigrinum) belonging to a laboratory research population presented with chronic cutaneous “cysts” that had reportedly progressed to “tumor-like swellings” over the dorsal midline. Empirical treatment with silver sulfadiazine twice weekly had been unsuccessful at resolving lesions. Skin impression smears and scrapes obtained from cutaneous lesions on two live individuals contained abundant, mixed bacteria, predominantly gram-positive, acid-fast negative and gram-negative rods, with phagocytosis by histiocytes. Necropsy of the most severely affected individual, a four-year-old female, revealed a well-defined and irregularly marginated region of dark discoloration and roughened surface along the dorsal midline with multifocal, soft, pale pink, solid dermal to subcutaneous nodules. Microscopically, the dermis and underlying skeletal muscle were disrupted by nodular, densely cellular populations of epithelioid macrophages, multinucleated giant cells, and fewer eosinophils along with foci of necrosis. Individual and clusters of pigmented muriform (fungal) cells and rare hyphae were scattered intracellularly and extracellularly throughout the areas of inflammation and necrosis. Muriform cells were round, approximately 9-12 μm in diameter with a thin, darkly pigmented capsule, a central, foamy, clear to lightly basophilic cytoplasm, and occasionally a midline division. Fungal culture yielded a melanized fungus morphologically and molecularly identified as Veronaea botryosa with 100% nucleotide similarity within the internal transcribed spacer region (609 bp). Chromomycosis is a chronic disease affecting a wide variety of amphibians and is caused by multiple species of pigmented fungi. Veronaea botryosa is a zoonotic pathogen and reported as a cause of chromomycosis and phaeohyphomycosis in anurans including White's tree frogs (Litoria caerulea), false tomato frogs (Dyscophus guineti), and eastern-Japanese common toads (Bufo japonicus formosus). To the authors' knowledge, this case represents the first detection of V. botryosa infection in a urodelian host.