331
Disease Control
Disease Resistant Fish A difference in susceptibility of channel catfi sh to Edw.
ictaluri infection was reported, and attributed to genetic factors (Camp et al. 2000 ).
Whereas both sensitive and resistant fi sh produced antibodies to Edw. ictaluri, the
later produced more T lymphocytes in peripheral blood and more macrophage
aggregations in the posterior kidney and spleen (Camp et al. 2000 ).
Vaccine Development Studies have been carried out to demonstrate the feasibility
of developing a vaccine against Edw. ictaluri (Plumb 1984 ). Fortunately, the organism is highly immunogenic, with agglutination titres of 1:10 000 found in the serum
of channel catfi sh after receiving only single injections of Edw. ictaluri cells mixed
in Freund’s adjuvant (cited in Plumb 1984 ). Furthermore, Saeed ( 1983 ) and Saeed
and Plumb ( 1987 ), using a LPS extract, demonstrated protection following i.p.
injection. In these experiments, 0.2 mg of LPS injected into channel catfi sh (individual weight = 60 g) induced agglutination titres of >1:500, which was suffi cient to
confer ≥80 % survival of the population. This compared with <30 % survival of the
unvaccinated controls. Antigenicity of the LPS extract was enhanced in FCA, with
protection conferred by single or multiple injections. Similarly, it should be emphasised that an inactivated whole-cell vaccine administered with FCA also showed
promise. Immersion and oral boosting of channel catfi sh fry with a commercial
vaccine was successful at controlling mortalities (Plumb and Vinitnantharat 1993 ).
With this study, mortalities were as follows:
controls:
96.7 % mortalities
immersion vaccinated group
6.7 % mortalities
Immersion vaccinated + oral boosted group
3.3 % mortalities
In a comparison of techniques (immersion, immersion and oral in combination,
and injection), injection led to the highest antibody titre after 10 weeks in channel
catfi sh fry (Thune et al. 1997 ). However, a booster by immersion after 25 weeks
gave a signifi cant increase in titre. A modern approach refl ected the development of
an adenine-auxotrophic strain, the virulence of which was attenuated (Lawrence
et al. 1997 ). Following injection, fi sh were protected against challenge with a virulent culture. An aroA mutant achieved success as a live vaccine (Thune et al. 1999 ).
Also, an isogenic transposon-generated O polysaccharide mutant strain was evaluated as a vaccine administered intraperitoneally and immersion to channel catfi sh,
and achieved useful protection (Lawrence and Banes 2005 ). A novobiocin-resistant
attenuated strain has been proposed as a vaccine, and applied to channel catfi sh by
i.p. injection with 4.2 × 10
6 CFU/fi sh of by immersion. Challenge led to an RPS of
>90 % [100 % for immersion vaccination] (Pridgeon and Klesius 2011 ). Interest in
live attenuated vaccines continued with the work of Wise et al. ( 2015 ), who attenuated a virulent isolate, S97-773, by repeated sub-culturing on laboratory media containing increasing concentrations of rifamycin. The cells were applied to feed at a
Edwardsiella ictaluri
Disease Control
Disease Resistant Fish A difference in susceptibility of channel catfi sh to Edw.
ictaluri infection was reported, and attributed to genetic factors (Camp et al. 2000 ).
Whereas both sensitive and resistant fi sh produced antibodies to Edw. ictaluri, the
later produced more T lymphocytes in peripheral blood and more macrophage
aggregations in the posterior kidney and spleen (Camp et al. 2000 ).
Vaccine Development Studies have been carried out to demonstrate the feasibility
of developing a vaccine against Edw. ictaluri (Plumb 1984 ). Fortunately, the organism is highly immunogenic, with agglutination titres of 1:10 000 found in the serum
of channel catfi sh after receiving only single injections of Edw. ictaluri cells mixed
in Freund’s adjuvant (cited in Plumb 1984 ). Furthermore, Saeed ( 1983 ) and Saeed
and Plumb ( 1987 ), using a LPS extract, demonstrated protection following i.p.
injection. In these experiments, 0.2 mg of LPS injected into channel catfi sh (individual weight = 60 g) induced agglutination titres of >1:500, which was suffi cient to
confer ≥80 % survival of the population. This compared with <30 % survival of the
unvaccinated controls. Antigenicity of the LPS extract was enhanced in FCA, with
protection conferred by single or multiple injections. Similarly, it should be emphasised that an inactivated whole-cell vaccine administered with FCA also showed
promise. Immersion and oral boosting of channel catfi sh fry with a commercial
vaccine was successful at controlling mortalities (Plumb and Vinitnantharat 1993 ).
With this study, mortalities were as follows:
controls:
96.7 % mortalities
immersion vaccinated group
6.7 % mortalities
Immersion vaccinated + oral boosted group
3.3 % mortalities
In a comparison of techniques (immersion, immersion and oral in combination,
and injection), injection led to the highest antibody titre after 10 weeks in channel
catfi sh fry (Thune et al. 1997 ). However, a booster by immersion after 25 weeks
gave a signifi cant increase in titre. A modern approach refl ected the development of
an adenine-auxotrophic strain, the virulence of which was attenuated (Lawrence
et al. 1997 ). Following injection, fi sh were protected against challenge with a virulent culture. An aroA mutant achieved success as a live vaccine (Thune et al. 1999 ).
Also, an isogenic transposon-generated O polysaccharide mutant strain was evaluated as a vaccine administered intraperitoneally and immersion to channel catfi sh,
and achieved useful protection (Lawrence and Banes 2005 ). A novobiocin-resistant
attenuated strain has been proposed as a vaccine, and applied to channel catfi sh by
i.p. injection with 4.2 × 10
6 CFU/fi sh of by immersion. Challenge led to an RPS of
>90 % [100 % for immersion vaccination] (Pridgeon and Klesius 2011 ). Interest in
live attenuated vaccines continued with the work of Wise et al. ( 2015 ), who attenuated a virulent isolate, S97-773, by repeated sub-culturing on laboratory media containing increasing concentrations of rifamycin. The cells were applied to feed at a
Edwardsiella ictaluri