'Winter ulcer' in the Atlantic salmon Salmo salar. Pathological and bacteriological investigations and transmission experiments

Abstract

ABSTRACT. The present study describes pathological changes and bacteriological findings in 'winter ulcer' in Atlantic salmon Salmo salar L. The transmissibility of the disease was also evaluated under experimental conditions. Skin changes were characterized by ulcers of varying size, and were categorized as acute to subacute, chronic, and regenerative/reparative. In the acute stages, lesions were superficial with scale loss and mild inflammation, while in the subacute stages ulcers were present that extended down to the underlying n~uscle. Histologically, the chronic stages were characterized by a severe inflammation of the dermis and of the interstitial muscle tissue. In the regeneration/reparation stages, a hyperplastic epidermis covered granulation tissue. Bacteriological investigations carried out in salmon sampled from 8 different farms with winter ulcer identified 2 groups of bacteria that were common in affected fish. The examinations performed in the present study indicate that both these groups belonged to the genus Vibrio, termed sp. 1 and sp. 2, respectively. Immunohistochemically, Vibrio sp. 1 and 2 were identified in situ associated with muscle tissue degeneration. Experimental infection with Vibno sp. 1 induced a disease similar to winter ulcer in Atlantic salmon, while inoculation with Vibrio sp. 2 had no effect. Cohabitation experiments showed that winter ulcer can be transmitted from diseased to healthy individuals, and that injection was not required to induce the process. However, mechanical skin lesions were a predisposing factor for ulcer formation. The present study provides evidence that winter ulcer is caused by an infection with a Vibrio-like bacterium, and that the disease can be transmitted through cohabitation and injection Pathological changes were not pathognomonic, and the severity of changes varied.

Previously unrecognised division within Moritella viscosa isolated from fish farmed in the North Atlantic

“…The observed pathological changes were in accordance with previous descriptions of infection with Moritella viscosa (Lunder et al 1995, Bruno et al 1998. The histopathology of skin ulcers revealed subepidermal oedema, dermal inflammation, haemorrhage and inflammation in subcutis and underlying red muscle and some necrosis of white muscle fibers.…”

Tenacibaculum sp. associated with winter ulcers in sea-reared Atlantic salmon Salmo salar

“…Studies based on cultivation alone report Moritella viscosa and to some extent Vibrio wodanis, as the most important specific bacteriological results related to this condition (Lunder et al 1995, Benediktsdóttir et al 1998, Bruno et al 1998. In those studies, M. viscosa was the dominating finding in 30, 40 and 40% of the outbreaks investigated, respectively.…”

“…Dis Aquat Org 94: [189][190][191][192][193][194][195][196][197][198][199] 2011 winter ulcers (Lunder et al 1995, Benediktsdóttir et al 1998; however, demonstration of pathogenicity for this bacterium under experimental conditions has so far been unsuccessful (Lunder et al 1995). Many culture-based investigations of winter ulcers have resulted in the identification of mixed cultures of mainly Vibrio spp.…”

“…Vibrio viscosus) is considered to be an important factor in the pathogenesis of winter ulcers in Norway, Iceland and Scotland (Lunder et al 1995, Benediktsdóttir et al 1998, Bruno et al 1998. M. viscosa has been shown to cause skin ulcers, septicaemia and mortality in transmission experiments (Lunder et al 1995, Løvoll et al 2009). Despite the availability and widespread use of vaccines against M. viscosa, winter ulcers remains a significant threat.…”

Aliivibrio finisterrensis sp. nov., isolated from Manila clam, Ruditapes philippinarum and emended description of the genus Aliivibrio

“…A. salmonicida described by Egidius et al (1986), is a psychrophilic species known as the causative agent of cold water vibriosis (Colquhoun & Sørum, 2001) or the Hitra disease affecting Atlantic salmon (Salmo salar) (Egidius et al, 1981). A. wodanis (Lunder et al, 2000) also affects Atlantic salmon and has been associated with the winter ulcer disease (Lunder et al, 1995). A. logei shares characteristics with the other members of the genus.…”