105
of iodine (i.e. 10.1 μg/g). This theme was continued by Bell et al. ( 1984 ), who
investigated the effects of sodium-L-ascorbate, zinc, iron and manganese as dietary
supplements on the manifestation of BKD. They noted that survival time was
inversely related to dietary ascorbate levels when the food was otherwise low in zinc
and manganese.
Disinfection Disinfection of egg surfaces has also been utilised to control
BKD. Iodophors, at 25–100 mg/l for 5 min, have proved benefi cial at reducing
transmission of the disease (Amend and Pietsch 1972 ; Ross and Smith 1972 ;
Bullock et al. 1978 ), although they will not eliminate the pathogen from inside
eggs (Evelyn et al. 1984 ). The use of erythromycin phosphate, at 1–2 mg/l for
30 min, has been advocated as an additive for water-hardening of eggs (Klontz
1978 ). However, it is debatable whether or not it is wise to use antibiotics in this
way.
Another approach has been to disinfect the water in fi sh farms. In particular, a
level of only 0.05 mg of free chlorine/l was suffi cient to inactivate cells of the pathogen in 18 s (Pascho et al. 1995 ). With such rapid inactivation, there must surely be
a use for the technique in hatcheries.
Use of Antimicrobial Compounds Chemotherapy offers some promise of success
(Bandín et al. 1991 ). Although BKD has become regarded as one of the most diffi -
cult bacterial fi sh diseases to treat (Bullock et al. 1975 ; Fryer and Sanders 1981 ),
some success at chemotherapy has been reported with erythromycin (Wolf and
Dunbar 1959 ), sulphonamides (Rucker et al. 1951 ), chloramphenicol (Rucker et al.
1953 ; Wood and Wallis 1955 ; Millan 1977 ), penicillin (Decew 1972 ), clindamycin,
kitasamycin and spiramycin (Austin 1985 ) and enrofl oxacin [Baytril] (Hsu et al.
1994 ). A MIC of 0.25–05 μg of enrofl oxacin/ml was calculated (Hsu et al. ( 1994 ).
Furthermore, some benefi cial effects have been indicated from trials using a dose of
20 mg of enrofl oxacin/kg body weight/day for 10 days when there was a reduction
in mortalities compared to controls. Over two trials, the deaths in the treated groups
and the controls were 43 % and 72 %, and 93 % and 100 %, respectively (Hsu et al.
1994 ). In addition, cephradine, lincomycin and rifampicin were found to be effective for prophylaxis of BKD, although they were of no use for therapeutic purposes
(Austin 1985 ). Undoubtedly, many of the problems with control measures revolve
around the intracellular nature of the organism (Young and Chapman 1978 ). Quite
simply, many of the drugs probably do not reach the actual foci of infection.
Nevertheless, experiments with liposomes, which target drugs to given organs,
proved to be disastrous, insofar as BKD was exacerbated (Austin 1985 ). Perhaps,
the value of micro- encapsulation techniques should be assessed.
The pioneering work with drugs for the control of BKD was undertaken by
Rucker et al. ( 1951 ). They reported a decrease in the level of mortalities following
the administration of sulphadiazine, via the oral route, at 250 mg of drug/kg body
weight of fi sh/day for 15 days. This was confi rmed by Earp et al. ( 1953 ) and Allison
( 1958 ). However, the drug failed to eliminate the pathogen from the fi sh.
Subsequently, Wolf and Dunbar ( 1959 ) in a comparison of 34 compounds concluded
Renibacterium salmoninarum
of iodine (i.e. 10.1 μg/g). This theme was continued by Bell et al. ( 1984 ), who
investigated the effects of sodium-L-ascorbate, zinc, iron and manganese as dietary
supplements on the manifestation of BKD. They noted that survival time was
inversely related to dietary ascorbate levels when the food was otherwise low in zinc
and manganese.
Disinfection Disinfection of egg surfaces has also been utilised to control
BKD. Iodophors, at 25–100 mg/l for 5 min, have proved benefi cial at reducing
transmission of the disease (Amend and Pietsch 1972 ; Ross and Smith 1972 ;
Bullock et al. 1978 ), although they will not eliminate the pathogen from inside
eggs (Evelyn et al. 1984 ). The use of erythromycin phosphate, at 1–2 mg/l for
30 min, has been advocated as an additive for water-hardening of eggs (Klontz
1978 ). However, it is debatable whether or not it is wise to use antibiotics in this
way.
Another approach has been to disinfect the water in fi sh farms. In particular, a
level of only 0.05 mg of free chlorine/l was suffi cient to inactivate cells of the pathogen in 18 s (Pascho et al. 1995 ). With such rapid inactivation, there must surely be
a use for the technique in hatcheries.
Use of Antimicrobial Compounds Chemotherapy offers some promise of success
(Bandín et al. 1991 ). Although BKD has become regarded as one of the most diffi -
cult bacterial fi sh diseases to treat (Bullock et al. 1975 ; Fryer and Sanders 1981 ),
some success at chemotherapy has been reported with erythromycin (Wolf and
Dunbar 1959 ), sulphonamides (Rucker et al. 1951 ), chloramphenicol (Rucker et al.
1953 ; Wood and Wallis 1955 ; Millan 1977 ), penicillin (Decew 1972 ), clindamycin,
kitasamycin and spiramycin (Austin 1985 ) and enrofl oxacin [Baytril] (Hsu et al.
1994 ). A MIC of 0.25–05 μg of enrofl oxacin/ml was calculated (Hsu et al. ( 1994 ).
Furthermore, some benefi cial effects have been indicated from trials using a dose of
20 mg of enrofl oxacin/kg body weight/day for 10 days when there was a reduction
in mortalities compared to controls. Over two trials, the deaths in the treated groups
and the controls were 43 % and 72 %, and 93 % and 100 %, respectively (Hsu et al.
1994 ). In addition, cephradine, lincomycin and rifampicin were found to be effective for prophylaxis of BKD, although they were of no use for therapeutic purposes
(Austin 1985 ). Undoubtedly, many of the problems with control measures revolve
around the intracellular nature of the organism (Young and Chapman 1978 ). Quite
simply, many of the drugs probably do not reach the actual foci of infection.
Nevertheless, experiments with liposomes, which target drugs to given organs,
proved to be disastrous, insofar as BKD was exacerbated (Austin 1985 ). Perhaps,
the value of micro- encapsulation techniques should be assessed.
The pioneering work with drugs for the control of BKD was undertaken by
Rucker et al. ( 1951 ). They reported a decrease in the level of mortalities following
the administration of sulphadiazine, via the oral route, at 250 mg of drug/kg body
weight of fi sh/day for 15 days. This was confi rmed by Earp et al. ( 1953 ) and Allison
( 1958 ). However, the drug failed to eliminate the pathogen from the fi sh.
Subsequently, Wolf and Dunbar ( 1959 ) in a comparison of 34 compounds concluded
Renibacterium salmoninarum