257
the determination of antibiogrammes. Notwithstanding such drawbacks, ELISA is a
valuable tool for the rapid detection of Aer. salmonicida in clinically diseased and
asymptomatic carrier fi sh.
It has not been conclusively established which organs of carrier fi sh serve as the
site of carriage. From experiments using immunofl uorescence techniques, Klontz
( 1968 ) concluded that the intestine is a primary site of infection, leading to the
establishment of asymptomatic carriers. There is also some evidence to suggest that
the kidney is involved, but the intestinal tract has again been mentioned (McCarthy
1980 ). This is a subject which requires further work to clarify it.
Another problematic aspect of the carrier state is that antibiotic therapy to control furunculosis outbreaks does not necessarily completely remove the bacterium
from the tissues of fi sh, at least when sulphamerazine, furazolidone and potentiated
sulphonamides are used. McCarthy ( 1980 ), however, reported that fi sh treated with
tetracycline hydrochloride (i.m. injection of 50 mg/kg) survived attempts to induce
the disease. On the basis of such fi ndings, McCarthy ( 1980 ) warned that it must be
anticipated that fi sh populations treated for furunculosis will remain carriers.
However more recently, other antibacterial compounds have been investigated
for their ability to reduce or eliminate the carrier state of Aer. salmonicida in fi sh.
Examples include erythromycin phosphate (Roberts 1980 ), fl umequine, and an
aryl-fl uoroquinolone (Scallen and Smith 1985 ) in combination with 0.01 % Tween
80 to enhance the assimilation of the antimicrobial compound into fi sh (Markwardt
et al. 1989 ). The last mentioned group of workers found that the aryl- fl uoroquinolone/
surfactant combination was effective in eliminating the asymptomatic carrier state
of Aer. salmonicida within 48 h of treatment. Markwardt and Klontz (1989) also
pointed out the advantages of the use of the aryl-fl uoroquinolone, such as its broad
spectrum activity, low in vitro minimal inhibitory concentration for many bacterial
pathogens (Stamm et al. 1986 ), and lack of occurrence of resistant strains (Fernandes
et al. 1987 ).
Aeromonas salmonicida – Transmission; What Does It All Mean? Several possible routes for the transmission of furunculosis have been propounded and investigated. It is commonly accepted that the disease is disseminated by lateral
transmission of Aer. salmonicida which includes contact with contaminated water
and infected fi sh in addition to possible infection via the gastro-intestinal tract.
Also, vertical transmission has been considered in several investigations. A waterborne route where water contamination with Aer. salmonicida has occurred initially
from moribund infected fi sh or from overtly healthy carriers shedding the pathogen
is favoured as the common means of transmission. Once released into the aquatic
environment, the organism is then able to persist for a prolonged period of time and
the disease spread in this way. Early studies demonstrated that trout placed into
water that had contained diseased fi sh contracted the infection (Emmerich and
Weibel 1894 ; Horne 1928 ; Blake and Clark 1931 ). The Furunculosis Committee of
the UK concluded, on the basis of available data, that both food and diseased fi sh
could constitute sources of infection. McCarthy ( 1980 ) has examined in detail the
likely transmission mechanisms, specifi cally with regard to the ability of Aer. salAeromonas salmonicida
the determination of antibiogrammes. Notwithstanding such drawbacks, ELISA is a
valuable tool for the rapid detection of Aer. salmonicida in clinically diseased and
asymptomatic carrier fi sh.
It has not been conclusively established which organs of carrier fi sh serve as the
site of carriage. From experiments using immunofl uorescence techniques, Klontz
( 1968 ) concluded that the intestine is a primary site of infection, leading to the
establishment of asymptomatic carriers. There is also some evidence to suggest that
the kidney is involved, but the intestinal tract has again been mentioned (McCarthy
1980 ). This is a subject which requires further work to clarify it.
Another problematic aspect of the carrier state is that antibiotic therapy to control furunculosis outbreaks does not necessarily completely remove the bacterium
from the tissues of fi sh, at least when sulphamerazine, furazolidone and potentiated
sulphonamides are used. McCarthy ( 1980 ), however, reported that fi sh treated with
tetracycline hydrochloride (i.m. injection of 50 mg/kg) survived attempts to induce
the disease. On the basis of such fi ndings, McCarthy ( 1980 ) warned that it must be
anticipated that fi sh populations treated for furunculosis will remain carriers.
However more recently, other antibacterial compounds have been investigated
for their ability to reduce or eliminate the carrier state of Aer. salmonicida in fi sh.
Examples include erythromycin phosphate (Roberts 1980 ), fl umequine, and an
aryl-fl uoroquinolone (Scallen and Smith 1985 ) in combination with 0.01 % Tween
80 to enhance the assimilation of the antimicrobial compound into fi sh (Markwardt
et al. 1989 ). The last mentioned group of workers found that the aryl- fl uoroquinolone/
surfactant combination was effective in eliminating the asymptomatic carrier state
of Aer. salmonicida within 48 h of treatment. Markwardt and Klontz (1989) also
pointed out the advantages of the use of the aryl-fl uoroquinolone, such as its broad
spectrum activity, low in vitro minimal inhibitory concentration for many bacterial
pathogens (Stamm et al. 1986 ), and lack of occurrence of resistant strains (Fernandes
et al. 1987 ).
Aeromonas salmonicida – Transmission; What Does It All Mean? Several possible routes for the transmission of furunculosis have been propounded and investigated. It is commonly accepted that the disease is disseminated by lateral
transmission of Aer. salmonicida which includes contact with contaminated water
and infected fi sh in addition to possible infection via the gastro-intestinal tract.
Also, vertical transmission has been considered in several investigations. A waterborne route where water contamination with Aer. salmonicida has occurred initially
from moribund infected fi sh or from overtly healthy carriers shedding the pathogen
is favoured as the common means of transmission. Once released into the aquatic
environment, the organism is then able to persist for a prolonged period of time and
the disease spread in this way. Early studies demonstrated that trout placed into
water that had contained diseased fi sh contracted the infection (Emmerich and
Weibel 1894 ; Horne 1928 ; Blake and Clark 1931 ). The Furunculosis Committee of
the UK concluded, on the basis of available data, that both food and diseased fi sh
could constitute sources of infection. McCarthy ( 1980 ) has examined in detail the
likely transmission mechanisms, specifi cally with regard to the ability of Aer. salAeromonas salmonicida