538
Disease Resistant Fish There is contradictory evidence about the role of genetically resistant fi sh strains at conferring resistance to vibriosis. Winter et al. ( 1979 )
determined that there was no variation in resistance to vibriosis among different
transferrin genotypes of coho salmon and steelhead trout. We support this observation, with regards to rainbow trout. However in contrast, Pratschner ( 1978 ) reported
the presence of differential resistance to vibriosis between transferrin genotypes of
coho salmon. More recently, an association has been made between polymorphism
in the major histocompatibility complex (MHC) 11α genes in Japanese fl ounder
( Paralichthys olivaceus ) and resistance to V. anguillarum whereby three alleles,
Paol-DAA*1301 , Paol-DAA*1401 and Paol-DAA*2201 , were associated signifi -
cantly with resistance (Xu et al. 2010 ). Furthermore, a relationship has been mooted
between alleles of MHC class II A genes and disease resistance in half smooth
tongue sole (Li et al. 2012 ).
Vaccine Development V. anguillarum has been one of the few successful candidates for vaccine development. Commercial formalin-inactivated whole cell vaccines are available, which have gained widespread use in mariculture. The benefi t of
these products is attested by their success in Atlantic halibut (Bricknell et al. 2000 ;
Bowden et al. 2002 ), African catfi sh (Vervarcke et al. 2004 ) and sea bass (Angelidis
et al. 2006 ) when after application by bathing and following challenge, complete
protection was recorded (RPS = 100 %). An immersion product developed for cod
led to an RPS of >80 % against V. anguillarum O2a and O2b (Mikkelsen et al. 2007 ).
Ironically, the reasons for the success of these products are often obscure, although
there is evidence that one commercial formalin-inactivated whole cells vaccine
induces the Mx gene (these are inducible by Type I interferons and have a role in
antiviral activity) expression in Atlantic salmon after administration intraperitoneally (Acosta et al. 2004 ). Moreover, there is some evidence to suggest that vaccinated fi sh generally fare much better, i.e. they exhibit better all-round health and
growth characteristics, than the unvaccinated counterparts. Moreover, immunostimulants, e.g. levamisole, further enhance protection (Kajita et al. 1990 ).
The immunogenicity appears to be a refl ection on the presence of heat-stable (to
100–121 °C) LPS in the cell wall (Salati et al. 1989b ; Kawai and Kusuda 1995 ),
which may be released in the culture supernatant (Chart and Trust 1984 ; Evelyn
1984 ), and OMP (Boesen et al. 1997 ). It has been postulated that a probable mechanism of protection concerns the inhibition of bacterial attachment by unknown factors in the skin mucus (Kawai and Kusuda 1995 ). That supernatants are also among
the most immunogenic parts of V. anguillarum vaccines was verifi ed following the
anal uptake of different vaccine fractions in carp and rainbow trout (Joosten et al.
1996 ). The large molecular weight LPS, i.e. 100 kDa (Evelyn and Ketcheson 1980 ),
are considered to confer protection to the recipient host. Moreover, the compounds
are able to withstand severe extraction methods. Also, Chart and Trust ( 1984 ) isolated, from the outer membrane, two minor proteins with molecular weights of
49–51 kDa, which were potent antigens. A weakly antigenic protein, with a molecular weight of ~40 kDa was also present. Perhaps, these are heat-labile, and explain
the reasons for the greater protection achieved with formalin-inactivated vaccines
10 Vibrios
Disease Resistant Fish There is contradictory evidence about the role of genetically resistant fi sh strains at conferring resistance to vibriosis. Winter et al. ( 1979 )
determined that there was no variation in resistance to vibriosis among different
transferrin genotypes of coho salmon and steelhead trout. We support this observation, with regards to rainbow trout. However in contrast, Pratschner ( 1978 ) reported
the presence of differential resistance to vibriosis between transferrin genotypes of
coho salmon. More recently, an association has been made between polymorphism
in the major histocompatibility complex (MHC) 11α genes in Japanese fl ounder
( Paralichthys olivaceus ) and resistance to V. anguillarum whereby three alleles,
Paol-DAA*1301 , Paol-DAA*1401 and Paol-DAA*2201 , were associated signifi -
cantly with resistance (Xu et al. 2010 ). Furthermore, a relationship has been mooted
between alleles of MHC class II A genes and disease resistance in half smooth
tongue sole (Li et al. 2012 ).
Vaccine Development V. anguillarum has been one of the few successful candidates for vaccine development. Commercial formalin-inactivated whole cell vaccines are available, which have gained widespread use in mariculture. The benefi t of
these products is attested by their success in Atlantic halibut (Bricknell et al. 2000 ;
Bowden et al. 2002 ), African catfi sh (Vervarcke et al. 2004 ) and sea bass (Angelidis
et al. 2006 ) when after application by bathing and following challenge, complete
protection was recorded (RPS = 100 %). An immersion product developed for cod
led to an RPS of >80 % against V. anguillarum O2a and O2b (Mikkelsen et al. 2007 ).
Ironically, the reasons for the success of these products are often obscure, although
there is evidence that one commercial formalin-inactivated whole cells vaccine
induces the Mx gene (these are inducible by Type I interferons and have a role in
antiviral activity) expression in Atlantic salmon after administration intraperitoneally (Acosta et al. 2004 ). Moreover, there is some evidence to suggest that vaccinated fi sh generally fare much better, i.e. they exhibit better all-round health and
growth characteristics, than the unvaccinated counterparts. Moreover, immunostimulants, e.g. levamisole, further enhance protection (Kajita et al. 1990 ).
The immunogenicity appears to be a refl ection on the presence of heat-stable (to
100–121 °C) LPS in the cell wall (Salati et al. 1989b ; Kawai and Kusuda 1995 ),
which may be released in the culture supernatant (Chart and Trust 1984 ; Evelyn
1984 ), and OMP (Boesen et al. 1997 ). It has been postulated that a probable mechanism of protection concerns the inhibition of bacterial attachment by unknown factors in the skin mucus (Kawai and Kusuda 1995 ). That supernatants are also among
the most immunogenic parts of V. anguillarum vaccines was verifi ed following the
anal uptake of different vaccine fractions in carp and rainbow trout (Joosten et al.
1996 ). The large molecular weight LPS, i.e. 100 kDa (Evelyn and Ketcheson 1980 ),
are considered to confer protection to the recipient host. Moreover, the compounds
are able to withstand severe extraction methods. Also, Chart and Trust ( 1984 ) isolated, from the outer membrane, two minor proteins with molecular weights of
49–51 kDa, which were potent antigens. A weakly antigenic protein, with a molecular weight of ~40 kDa was also present. Perhaps, these are heat-labile, and explain
the reasons for the greater protection achieved with formalin-inactivated vaccines
10 Vibrios