281
The Fate of Aeromonas salmonicida Following Infection
Workers have addressed the questions concerning the fate of Aer. salmonicida after
infection by various routes. Some of this information is discussed elsewhere. Using
radio-active methods, Svendsen et al. ( 1999 ) published evidence that following
infection by immersion, the pathogen could be readily found around surface wounds
(the Atlantic salmon had been artifi cially wounded prior to use), the gills and hindgut (radioactivity increased here from 2 to 24 h). Two hours after challenge, bacteria
were detected in the blood; at 24 h Aer. salmonicida was in the kidney but not the
blood (Svendsen et al. 1999 ). It is clear from recent work that the pathogen is able
to translocate across the salmonid intestinal epithelium. Using modifi ed Ussing
chambers and intestinal segments with fl uorescein-isothiocyanate labeling and fl uoremetry, Jutfeldt et al. ( 2008 ) considered the role for viable and heat-inactivated
cells, ECP and LPS, determining that live cells translocated better than inactivated
cells.
Disease Control
Disease Resistant Fish Embody and Hayford ( 1925 ) increased resistance in brook
trout to furunculosis by selective breeding. Subsequently, Wolf ( 1954 ) reported the
start of an investigation aimed at developing ulcer disease and furunculosis-resistant
strains of brook trout and brown trout. Five years later, Snieszko et al. ( 1959 ) concluded that disease was, indeed, genetically determined. Ehlinger ( 1964 , 1977 )
echoed this opinion by determining resistance to furunculosis in the progeny of
brook trout. Thereafter, a substantial leap forward in knowledge occurred following
a publication by Cipriano ( 1982c ), who reported varying degrees of resistance to
furunculosis among 11 different strains of rainbow trout, and correlated this with
the serum neutralisation titre. Cipriano determined that the McConnaughy strain
was the most susceptible, with 83 % of the animals dying within 14 days of challenge with 1.2 × 10
9 cells administered in a 1 min bath. The serum neutralisation
titre was 1:80 against one of the extracellular fractions of Aer. salmonicida. In contrast, there was no mortality among the Wytheville strain, which demonstrated a
serum neutralisation titre of 1:2560. Cipriano (1983) concluded that serum from
rainbow trout (which are naturally resistant to furunculosis) could protect passively
immunised brook trout from challenge with a virulent culture. In contrast, the
administration of serum from susceptible Atlantic salmon was unsuccessful in conferring resistance upon brook trout. The protective effect of rainbow trout serum
was believed to be attributed to the neutralisation of toxic components produced by
the pathogen. Some unpublished data have pointed to the ability of certain strains of
rainbow trout to tolerate the rigours of furunculosis. Genetic variation in susceptibility of Atlantic salmon has been examined in the study of one-year-old fi sh
(Gjedrem and Gjoen 1995 ). The differential resistance of four turbot families to Aer.
Aeromonas salmonicida
The Fate of Aeromonas salmonicida Following Infection
Workers have addressed the questions concerning the fate of Aer. salmonicida after
infection by various routes. Some of this information is discussed elsewhere. Using
radio-active methods, Svendsen et al. ( 1999 ) published evidence that following
infection by immersion, the pathogen could be readily found around surface wounds
(the Atlantic salmon had been artifi cially wounded prior to use), the gills and hindgut (radioactivity increased here from 2 to 24 h). Two hours after challenge, bacteria
were detected in the blood; at 24 h Aer. salmonicida was in the kidney but not the
blood (Svendsen et al. 1999 ). It is clear from recent work that the pathogen is able
to translocate across the salmonid intestinal epithelium. Using modifi ed Ussing
chambers and intestinal segments with fl uorescein-isothiocyanate labeling and fl uoremetry, Jutfeldt et al. ( 2008 ) considered the role for viable and heat-inactivated
cells, ECP and LPS, determining that live cells translocated better than inactivated
cells.
Disease Control
Disease Resistant Fish Embody and Hayford ( 1925 ) increased resistance in brook
trout to furunculosis by selective breeding. Subsequently, Wolf ( 1954 ) reported the
start of an investigation aimed at developing ulcer disease and furunculosis-resistant
strains of brook trout and brown trout. Five years later, Snieszko et al. ( 1959 ) concluded that disease was, indeed, genetically determined. Ehlinger ( 1964 , 1977 )
echoed this opinion by determining resistance to furunculosis in the progeny of
brook trout. Thereafter, a substantial leap forward in knowledge occurred following
a publication by Cipriano ( 1982c ), who reported varying degrees of resistance to
furunculosis among 11 different strains of rainbow trout, and correlated this with
the serum neutralisation titre. Cipriano determined that the McConnaughy strain
was the most susceptible, with 83 % of the animals dying within 14 days of challenge with 1.2 × 10
9 cells administered in a 1 min bath. The serum neutralisation
titre was 1:80 against one of the extracellular fractions of Aer. salmonicida. In contrast, there was no mortality among the Wytheville strain, which demonstrated a
serum neutralisation titre of 1:2560. Cipriano (1983) concluded that serum from
rainbow trout (which are naturally resistant to furunculosis) could protect passively
immunised brook trout from challenge with a virulent culture. In contrast, the
administration of serum from susceptible Atlantic salmon was unsuccessful in conferring resistance upon brook trout. The protective effect of rainbow trout serum
was believed to be attributed to the neutralisation of toxic components produced by
the pathogen. Some unpublished data have pointed to the ability of certain strains of
rainbow trout to tolerate the rigours of furunculosis. Genetic variation in susceptibility of Atlantic salmon has been examined in the study of one-year-old fi sh
(Gjedrem and Gjoen 1995 ). The differential resistance of four turbot families to Aer.
Aeromonas salmonicida