Duration of protective antibodies, and the correlation with protection in Atlantic salmon (Salmo salar L.), following vaccination with an Aeromonas salmonicida vaccine containing iron-regulated outer membrane proteins and secretory polysaccharide
Ir. Bricknell et al., Duration of protective antibodies, and the correlation with protection in Atlantic salmon (Salmo salar L.), following vaccination with an Aeromonas salmonicida vaccine containing iron-regulated outer membrane proteins and secretory polysaccharide, FISH SHELLF, 9(2), 1999, pp. 139-151
Atlantic salmon (n=82) were individually marked and injected intraperitonea
lly with an unadjuvanted A-layer negative (A) Aeromonas salmonicida bacteri
n which had been grown under iron-restricted conditions to induce expressio
n of iron-regulated outer membrane proteins (IROMPs). The bacterin was supp
lemented with the extracellular polysaccharide (PS) antigen which had been
extracted using hot phenol from the supernatant of a normal broth culture o
f A. salmonicida. Eight weeks after vaccination, the fish were bath-challen
ged with a virulent A. salmonicida strain. Specific antibody titres to IROM
Ps and PS were determined by ELISA. All 20 unvaccinated control fish died.
In the vaccinated fish 1 week prior to challenge, seven of the eight fish w
hich died had antibody titres to IROMPs of log(2) 1 or 2; the eighth fish h
ad log(2) titre of 5. With the exception of this individual, all fish with
log(2) titres greater than 4 survived the challenge (66 out of 67) while 47
% of fish with titres of log(2) 2 or below died (7 out of 15). Similar corr
elations of anti-PS antibody titres with protection were observed. Of those
fish with antibody responses to neither, only one or both antigens, 100% o
f non-responding fish died, 7.2% of responders to only one antigen, and 1.2
% pf responders to both antigens died. One month following challenge the an
tibody titres to IROMPs in surviving fish decreased by about 30% and therea
fter a monthly decrease of about 10% was observed. In contrast, the antibod
y titres in an identical but unchallenged vaccinated group continued to ris
e to a peak at week 12 and thereafter decreased by about 10% per month. Nin
e months after vaccination both groups were challenged. Similar relative pe
rcent survival was recorded in both groups (over 50%) and once again indivi
dual survival correlated strongly with anti-IROMP antibody titres before ch
allenge. Titres above log(2) 5 correlated with protection. This is the firs
t report of specific antibody responses having a strong correlation with pr
otection against furunculosis. (C) 1999 Academic Press