516
salmonicida. A similar plasmid composition has been indicated for isolates from the
Faroe Islands (Nielsen and Dalsgaard 1991 ). Comparing isolates from Canada,
Faroe Islands, Norway and Shetland, Sørum et al. ( 1993 ) noted a similarity in plasmid profi le, with three plasmids of 2.8, 3.4 and 21 mDa revealed. Furthermore, a
conclusion has been reached that all strains carry plasmids (Valla et al. 1992 ).
Differences have also been implied by serological studies, which have indicated the
presence of two serotypes (Schrøder et al. 1992 ).
DNA hybridisation of four cultures confi rmed homogeneity (DNA homology = 82 − 100 %), but low relatedness to V. anguillarum (30 %), V. ordalii (34 %) or
V. parahaemolyticus (40 %) (Wiik and Egidius 1986 ). Although these data were
used to justify the uniqueness of Ali. salmonicida, the relationship to other representatives of the family Vibrionaceae was not considered. The validity of the species is
not, however, questioned, and in the detailed study of Austin et al. ( 1997 ), Ali. salmonicida formed a discrete taxon among the other fi sh-pathogenic vibrios. Its transfer to Aliivibrio was an appropriate taxonomic move (Urbanczyk et al. 2007 ).
Epizootiology
It has been demonstrated that Ali. salmonicida survives for >14 months in laboratorybased experiments with sea water, when seeded at ~10
6 cells/ml (Hoff 1989 ). Thus,
there is the potential for long term survival in the vicinity of fi sh farms, as confi rmed
by Husevåg et al. ( 1991 ). Moreover, the pathogen has been detected in the sediment
(12–43 cells/ml) below fi sh farms, several months after an outbreak of Hitra disease.
In addition, Ali. salmonicida has been detected in the sediments from fi sh farms
which were not experiencing clinical disease (Enger et al. 1989 , 1991 ). Clearly,
there will be a reservoir of the pathogen around farmed fi sh, from which further
infections may occur. Attachment and colonisation of surfaces to surfaces to form
biofi lms is infl uenced by quorum sensing (Hansen et al. 2014 ).
Pathogenicity
Intraperitoneal injection and immersion of Atlantic salmon with broth cultures led to
clinical disease, with the pathogen appearing quickly, i.e. within 2 h, in the blood
suggesting the rapid development of a septicaemia (Bjelland et al. 2012 ), and in
which Ali. salmonicida either inhibits or resists the host’s innate immune system
(Bjelland et al. 2013 ). The intestine became colonized more slowly after immersion
challenge (Bjelland et al. 2012 ). Atlantic salmon were more susceptible than rainbow trout (Egidius et al. 1986 ; Hjeltnes et al. 1987 ). The LD 50 dose ranges from
4 × 10
6 − 1 × 10
8 cells/fi sh (Wiik et al. 1989 ). The presence of other acute disease diseases, such as infectious pancreatic necrosis, has exacerbated infections in Atlantic
salmon caused by Ali. salmonicida (Johansen and Sommer 2001 ). In addition, Ali.
10 Vibrios
salmonicida. A similar plasmid composition has been indicated for isolates from the
Faroe Islands (Nielsen and Dalsgaard 1991 ). Comparing isolates from Canada,
Faroe Islands, Norway and Shetland, Sørum et al. ( 1993 ) noted a similarity in plasmid profi le, with three plasmids of 2.8, 3.4 and 21 mDa revealed. Furthermore, a
conclusion has been reached that all strains carry plasmids (Valla et al. 1992 ).
Differences have also been implied by serological studies, which have indicated the
presence of two serotypes (Schrøder et al. 1992 ).
DNA hybridisation of four cultures confi rmed homogeneity (DNA homology = 82 − 100 %), but low relatedness to V. anguillarum (30 %), V. ordalii (34 %) or
V. parahaemolyticus (40 %) (Wiik and Egidius 1986 ). Although these data were
used to justify the uniqueness of Ali. salmonicida, the relationship to other representatives of the family Vibrionaceae was not considered. The validity of the species is
not, however, questioned, and in the detailed study of Austin et al. ( 1997 ), Ali. salmonicida formed a discrete taxon among the other fi sh-pathogenic vibrios. Its transfer to Aliivibrio was an appropriate taxonomic move (Urbanczyk et al. 2007 ).
Epizootiology
It has been demonstrated that Ali. salmonicida survives for >14 months in laboratorybased experiments with sea water, when seeded at ~10
6 cells/ml (Hoff 1989 ). Thus,
there is the potential for long term survival in the vicinity of fi sh farms, as confi rmed
by Husevåg et al. ( 1991 ). Moreover, the pathogen has been detected in the sediment
(12–43 cells/ml) below fi sh farms, several months after an outbreak of Hitra disease.
In addition, Ali. salmonicida has been detected in the sediments from fi sh farms
which were not experiencing clinical disease (Enger et al. 1989 , 1991 ). Clearly,
there will be a reservoir of the pathogen around farmed fi sh, from which further
infections may occur. Attachment and colonisation of surfaces to surfaces to form
biofi lms is infl uenced by quorum sensing (Hansen et al. 2014 ).
Pathogenicity
Intraperitoneal injection and immersion of Atlantic salmon with broth cultures led to
clinical disease, with the pathogen appearing quickly, i.e. within 2 h, in the blood
suggesting the rapid development of a septicaemia (Bjelland et al. 2012 ), and in
which Ali. salmonicida either inhibits or resists the host’s innate immune system
(Bjelland et al. 2013 ). The intestine became colonized more slowly after immersion
challenge (Bjelland et al. 2012 ). Atlantic salmon were more susceptible than rainbow trout (Egidius et al. 1986 ; Hjeltnes et al. 1987 ). The LD 50 dose ranges from
4 × 10
6 − 1 × 10
8 cells/fi sh (Wiik et al. 1989 ). The presence of other acute disease diseases, such as infectious pancreatic necrosis, has exacerbated infections in Atlantic
salmon caused by Ali. salmonicida (Johansen and Sommer 2001 ). In addition, Ali.
10 Vibrios