An ultrastructural study of morphological changes in Atlantic salmon, Salmo salar L., during the development of cold water vibriosis

Abstract

The structural changes which occur in the heart, the lateral muscle and the large intestine during the development of cold water vibriosis in Atlantic salmon, Salmo salar L., have been studied by light and electron microscopy. The results strongly suggest a causative relationship between the presence of the fish pathogen. Vibrio salmonicida, and the observed pathological changes. Cell damage was invariably accompanied by the presence of the bacterium. A close relationship was found between the number of bacteria detected in the tissues and the degree of morphological damage. The most severe cell damage was found in areas with a rich blood supply. The earliest sign of damage was detected in the cell coat and cell membrane on the luminal side of the endothelial cells of the capillaries. Later in the development, the bacteria were also found intracellularly in endothelial cells. In moribund fish, the cells in the vicinity of the capillaries were also severely damaged. Bacteria appeared intracellularly in leucocytes even in early stages of the disease. This caused more severe damage to leucocytes compared to erythrocytes, which seldom contained bacteria.

LitR of Vibrio salmonicida Is a Salinity-Sensitive Quorum-Sensing Regulator of Phenotypes Involved in Host Interactions and Virulence

“…Various virulence mechanisms, including protease activity and cytotoxicity, have been described for different Vibrio species (1,10,29,64). The tissue damage observed in fish suffering from CV may also be due to extracellular toxin activity (27,63). However, we examined the cytotoxicity in cell cultures according to protocols by Tunsjø et al (64), and we detected no cytopathogenic effects in any of six fish cell lines infected with LFI1238 or the ⌬litR mutant (unpublished results).…”

“…However, it should be noted that Hjelmeland et al (25) also failed to identify any extracellular cytotoxins or proteolytic enzymes in their study. Additionally, in the intestines of moribund salmon with CV, where V. salmonicida dominates the microbial flora, an absence of tissue damage of the epithelium has been reported (63). This suggests that V. salmonicida probably relies on mechanisms other than extracellular toxins to attack the host and escape its immune system.…”

Pathogenicity of vibrios in fish: An overview

“…ordalii Ransom et al, 1984 Summer flounder, Paralichthys dentatus Soffientino et al, 1999 V. carchariae Brown shark, Carcharkinus plumbeus Bertone et al, 1996Grouper, Epinephelus coioides Lee et al, 2002 V. carchariae Brown shark, Carcharhinus plumbeus damsela Spiny dogfish, Squalus aczznthias Grimes et al, 1984Grimes et al, , 1985 Zorrilla et al, 2003 !7. marinus Atlantic salmon, Salrno salar Benediktsdottir et al, 1998 mimicus Red sea bream, Pagrus major Wu and Pan, 2000 V. parahaemolyticus Iberian toothcarp, Aphanius iberus Alcaide et aL, 1999 V. pelagius Turbot, Scophthalmus maximus Villamil et al, 2003 a, b V. salmonicida Atlantic salmon, Salmo salar Totland and Nylund, 1988 Turbot, Scophthalmus maMmus Angulo et al, 1994 V. spIendidus Salte et al, 1994;V. viscosus Atlantic salmon, Salmo salar Lunder et al, 1995;Bruno et al, 1998;Greger and Goodrich, 1999 V. vulnificus Grouper, Epinephelus sp.…”

Structural studies of the O-antigenic oligosaccharide from Vibrio salmonicida strain C2 isolated from Atlantic cod, Gadus morhua L.

“…Light and electron microscopic studies showed necrotic tissues in the kidneys and bacteria in contact with injured endothelial cells. 8,9 Vaccines developed against coldwater vibriosis have been shown to give full protection against infection with V. salmonicida. 10 In spite of this, outbreaks of coldwater vibriosis occasionally occur in vaccinated Atlantic salmon.…”