282
salmonicida has been indicated, and may have signifi cance for breeding disease
resistant fi sh (Rodriguez-Ramilo et al. 2011 ).
Vaccine Development The development of an effective vaccine against the rigours
of Aer. salmonicida infections remains one of the great challenges to researchers.
Interest in vaccine development may be traced to the pioneering work of Duff
( 1942 ), who produced an orally administered, chloroform-inactivated whole-cell
preparation. It is enigmatic that his reported success has not been surpassed, and
indeed often not equaled, by subsequent workers. Unfortunately, efforts concerning
vaccine development languished as chemotherapy became established as the principal means of disease control. Eventually, however, aforementioned resistance problems with chemotherapeutants led researchers to recognise the need for alternative
control measures, and, thus, a resurgence of interest in vaccines ensued. However, it
now appears that Aer. salmonicida is an ineffi cient antigen, in terms of its overall
capability of stimulating a protective immune response (Tatner 1989 ). There is
some controversy over the effectiveness of formulations based on ECP. Some studies indicate that they may well be immunosuppressive (Sövényi et al. 1990 ), whereas
others describe their benefi t in terms of immunogenicity (Kawahara et al. 1990 ).
Notwithstanding, modern molecular techniques, principally the PCR, have demonstrated that vaccine antigens do get taken up into the body of fi sh, namely the head
kidney and spleen (Høie et al. 1996 ).
Some of the problems associated with vaccine development have been summarised below. Essentially, the problems refl ect economics, i.e. the perceived need
for low-cost products on the part of the fi sh farmer, versus the desire for substantial
profi t margins on the part of the vaccine manufacturer/suppliers. Scientifi c problems exist due to an incomplete understanding of the biology of Aer. salmonicida.
Specifi cally, progress has been hindered by the uncertainty surrounding the nature
of the antigenic components of Aer. salmonicida, the effect of strain differences
[n.b.: Gudmundsdóttir and Gudmundsdóttir 1997 while examining the cross protection of vaccines against typical and atypical isolates of Aer. salmonicida, concluded
that the best protection resulted with autogenous products], and the lack of a consistent and reliable challenge method, although the latter has been improved by the
development of effective cohabitation and bath methods (e.g. Bricknell 1995 ;
Nordmo et al. 1998 ). Injectable vaccines based on microencapsulation with V.
anguillarum LPS led to signifi cantly higher oxygen consumption, lysozyme activity, specifi c growth rates and antibody titre to Aer. salmonicida in rainbow trout than
fi sh which received inactivated whole cells with or without levamisole or emulsifi ed
oil as adjuvants, or microencapsulated with or without muramyl dipeptide or
ß-1,3-glucan (Ackerman et al. 2000 ). Severe side effects have resulted from the i.p.
injection of oil-adjuvanted vaccines, with the ECP component contributing to
infl ammation (Mutoloki et al. 2006 ) Intra-abdominal adhesions have been reported
in Atlantic salmon following the i.p. injection of oil-adjuvanted vaccines
(Gudmundsdóttir et al. 2003 ) with damage occurring from 10-weeks to 14-month
after injection (Villumsen et al. 2015 ). Also, there is evidence of temporary immu5 Aeromonadaceae Representative (Aeromonas salmonicida)
salmonicida has been indicated, and may have signifi cance for breeding disease
resistant fi sh (Rodriguez-Ramilo et al. 2011 ).
Vaccine Development The development of an effective vaccine against the rigours
of Aer. salmonicida infections remains one of the great challenges to researchers.
Interest in vaccine development may be traced to the pioneering work of Duff
( 1942 ), who produced an orally administered, chloroform-inactivated whole-cell
preparation. It is enigmatic that his reported success has not been surpassed, and
indeed often not equaled, by subsequent workers. Unfortunately, efforts concerning
vaccine development languished as chemotherapy became established as the principal means of disease control. Eventually, however, aforementioned resistance problems with chemotherapeutants led researchers to recognise the need for alternative
control measures, and, thus, a resurgence of interest in vaccines ensued. However, it
now appears that Aer. salmonicida is an ineffi cient antigen, in terms of its overall
capability of stimulating a protective immune response (Tatner 1989 ). There is
some controversy over the effectiveness of formulations based on ECP. Some studies indicate that they may well be immunosuppressive (Sövényi et al. 1990 ), whereas
others describe their benefi t in terms of immunogenicity (Kawahara et al. 1990 ).
Notwithstanding, modern molecular techniques, principally the PCR, have demonstrated that vaccine antigens do get taken up into the body of fi sh, namely the head
kidney and spleen (Høie et al. 1996 ).
Some of the problems associated with vaccine development have been summarised below. Essentially, the problems refl ect economics, i.e. the perceived need
for low-cost products on the part of the fi sh farmer, versus the desire for substantial
profi t margins on the part of the vaccine manufacturer/suppliers. Scientifi c problems exist due to an incomplete understanding of the biology of Aer. salmonicida.
Specifi cally, progress has been hindered by the uncertainty surrounding the nature
of the antigenic components of Aer. salmonicida, the effect of strain differences
[n.b.: Gudmundsdóttir and Gudmundsdóttir 1997 while examining the cross protection of vaccines against typical and atypical isolates of Aer. salmonicida, concluded
that the best protection resulted with autogenous products], and the lack of a consistent and reliable challenge method, although the latter has been improved by the
development of effective cohabitation and bath methods (e.g. Bricknell 1995 ;
Nordmo et al. 1998 ). Injectable vaccines based on microencapsulation with V.
anguillarum LPS led to signifi cantly higher oxygen consumption, lysozyme activity, specifi c growth rates and antibody titre to Aer. salmonicida in rainbow trout than
fi sh which received inactivated whole cells with or without levamisole or emulsifi ed
oil as adjuvants, or microencapsulated with or without muramyl dipeptide or
ß-1,3-glucan (Ackerman et al. 2000 ). Severe side effects have resulted from the i.p.
injection of oil-adjuvanted vaccines, with the ECP component contributing to
infl ammation (Mutoloki et al. 2006 ) Intra-abdominal adhesions have been reported
in Atlantic salmon following the i.p. injection of oil-adjuvanted vaccines
(Gudmundsdóttir et al. 2003 ) with damage occurring from 10-weeks to 14-month
after injection (Villumsen et al. 2015 ). Also, there is evidence of temporary immu5 Aeromonadaceae Representative (Aeromonas salmonicida)