Exophiala angulospora causes systemic ­inflammation in Atlantic cod Gadus morhua

Abstract

Species of Exophiala are opportunistic fungal pathogens that may infect a broad range of warm- and cold-blooded animals, including salmonids and Atlantic cod. In the present study, we observed abnormal swimming behaviour and skin pigmentation and increased mortality in cod kept in an indoor tank. Necropsy revealed foci of different sizes with a greyish to brownish colour in internal organs of diseased fish. The foci consisted of ramifying darkly pigmented fungal hyphae surrounded by distinct layers of inflammatory cells, including macrophage-like cells. In the inner layer with many hyphae, the macrophage-like cells were dead. We observed no apparent restriction of fungal growth by the inflammatory response. A darkly pigmented fungus was repeatedly isolated in pure culture from foci of diseased fish and identified as Exophiala angulospora using morphological and molecular characters. This species has not been previously reported to cause disease in cod, but has been reported as an opportunistic pathogen of both marine and freshwater fish. Based on the morphology and sequence analysis presented here, we conclude that E. angulospora caused the observed chronic multifocal inflammation in internal organs of cod, leading to severe disease and mortality.

Exophiala angulospora Causes Systemic Mycosis in Atlantic Halibut: a Case Report

“…Systemic mycosis caused by E. angulospora has been previously described from two marine fishes: Weedy Seadragon and Atlantic Cod. Similar to our observations, in the case of Atlantic Cod ingress was suggested to occur via the urinary tract to the kidney, as the kidney was found to be infected in all of the diseased fish examined (Gjessing et al 2011). Fungal ingress in Weedy Seadragons was believed to occur via the gill or skin through preexisting lesions such as abrasions (Nyaoke et al 2009).…”

“…Exophiala angulospora is a ubiquitous fungus, and reports of isolations have been made from water, decorticated wood, human skin and nails, soils, and diseased fish (de Hoog et al 2011;Gjessing et al 2011). Due to the ubiquitous nature of the fungus the origin of the E. angulospora inoculum found in the diseased Atlantic Halibut is unclear.…”

“…Exophiala angulospora has been reported to cause mycosis in aquaria-maintained Weedy Seadragons Phyllopteryx taeniolatus in the United States (Nyaoke et al 2009). This pathogen has also been isolated from Inconnu Stenodus leucichthys in southern Russia (de Hoog et al 2011) and was determined to be the cause of systemic mycosis in farmed Atlantic Cod Gadus morhua from Norway (Gjessing et al 2011). Necropsy of moribund cod revealed chronic multifocal inflammation in the internal organs, consisting of dematiaceous fungal hyphae surrounded by distinct layers of inflammatory cells.…”

“…are ubiquitous fungi, historically isolated from a variety of environmental substrates such as soil and sediment, decaying wood and plant material, human hair and nails, and drinking water (Iwatsu et al 1991;Domsch et al 2007;de Hoog et al 2011). These filamentous black yeasts are also opportunistic pathogens causing both superficial and systemic mycoses in warm-and cold-blooded animals (Uijthof et al 1997;de Hoog et al 2011;Gjessing et al 2011). de Hoog et al (2011 suggest that animals with moist skin are more susceptible to infection by filamentous black yeasts, where the ability of the pathogen to assimilate alkylbenzenes and accumulate melanin within the hyphae and conidia are purported to be general virulence factors for these agents.…”

“…Necropsy of moribund cod revealed chronic multifocal inflammation in the internal organs, consisting of dematiaceous fungal hyphae surrounded by distinct layers of inflammatory cells. Gjessing et al (2011) noted that the fungal infection was not eliminated by this inflammatory response in the cod, resulting in a systemic infection and mortality.…”