Phaeohyphomycosis due to Exophiala in Aquarium-Housed Lumpfish (Cyclopterus lumpus): Clinical Diagnosis and Description

Abstract

Phaeohyphomycosis caused by Exophiala species represents an important disease of concern for farmed and aquarium-housed fish. The objective of this study was to summarize the clinical findings and diagnosis of Exophiala infections in aquarium-housed Cyclopterus lumpus. Clinical records and postmortem pathology reports were reviewed for 15 individuals from 5 public aquaria in the United States and Canada from 2007 to 2015. Fish most commonly presented with cutaneous ulcers and progressive clinical decline despite topical or systemic antifungal therapy. Antemortem fungal culture of cutaneous lesions resulted in colonial growth for 7/12 samples from 8 individuals. Amplification of the internal transcribed spacer region (ITS) of nuclear rDNA identified Exophiala angulospora or Exophiala aquamarina in four samples from three individuals. Postmortem histopathologic findings were consistent with phaeohyphomycosis, with lesions most commonly found in the integument (11/15), gill (9/15), or kidney (9/15) and evidence of fungal angioinvasion and dissemination. DNA extraction and subsequent ITS sequencing from formalin-fixed paraffin-embedded tissues of seven individuals identified E. angulospora, E. aquamarina, or Cyphellophora sp. in four individuals. Lesion description, distribution, and Exophiala spp. identifications were similar to those reported in farmed C. lumpus. Antemortem clinical and diagnostic findings of phaeohyphomycosis attributable to several species of Exophiala provide insight on the progression of Exophiala infections in lumpfish that may contribute to management of the species in public aquaria and under culture conditions.

Keywords: Cyclopterus lumpus; Exophiala; lumpfish; melanized fungus; phaeohyphomycosis.

Figure A1

Maximum likelihood tree based on ITS showing the relationship of the isolates 9404 (UTHSC 15-2163); T12068 (UTHSC 13-1953), 3152 (UTHSC 07-871), and T12069 (UTHSC 13-1506) with representative Exophiala species and other species in the Herpotrichiellaceae. Numbers on the nodes indicate support values BI ≥ 0.95/BS ≥ 80%. * denotes BI = 1.00/BS = 100%. ^T = type species.

Figure 1

(a) Integumentary lesions representative of Exophiala infection in lumpfish. Ulcers are well demarcated with raised margins and central depressions. (b) Wet mount cytology of a cutaneous ulcer from the lumpfish in (a). Fungal hyphae are light brown and slender with parallel walls, transverse septa, and lateral branchings. (c) Exophiala infection of the heart from a lumpfish. Multiple, discrete, and occasionally coalescent, slightly raised, black foci are scattered in the ventricle and atrium. (d) Histologic section of the heart of a lumpfish with black multifocal lesions displayed in (c). Melanized fungal hyphae are numerous and form a mat extending from the epicardial surface and invading the underlying myocardium. H&E, bar = 200 µM.

Figure 1

(a) Integumentary lesions representative of Exophiala infection in lumpfish. Ulcers are well demarcated with raised margins and central depressions. (b) Wet mount cytology of a cutaneous ulcer from the lumpfish in (a). Fungal hyphae are light brown and slender with parallel walls, transverse septa, and lateral branchings. (c) Exophiala infection of the heart from a lumpfish. Multiple, discrete, and occasionally coalescent, slightly raised, black foci are scattered in the ventricle and atrium. (d) Histologic section of the heart of a lumpfish with black multifocal lesions displayed in (c). Melanized fungal hyphae are numerous and form a mat extending from the epicardial surface and invading the underlying myocardium. H&E, bar = 200 µM.

Figure 2

(a) Melanized (brown) fungal hyphae are present throughout a focus of the ventricular myocardium wherein many myocardial fibers are necrotic, represented by pale eosinophilic sarcoplasm lacking striations and nuclei or having pyknotic nuclei. (b) Melanized (brown) fungal hyphae course through the renal interstitium with many necrotic hematopoietic cells and tubules lined by necrotic epithelial cells having eosinophilic cytoplasm and pyknotic nuclei. H&E, bar = 20 µM.

Figure 3

Fungal angioinvasion and histochemical staining of hyphae for melanin. (a) Melanized fungal hyphae are located in the lumen of a blood vessel and throughout the surrounding dermis accompanied by a dermal infiltrate of mononuclear cells. Fontana–Masson, bar = 20 µM. (b) High-magnification image of dermis from (a). Hyphae are slender, with parallel walls, transverse septa, and lateral branching; hyphae are stained brown using the Fontana–Masson technique indicative of the presence of melanin. Fontana–Masson, bar = 10 µM.