716
Pathogenicity
There has been continual interest in the determination of pathogenicity mechanisms
with current focus placed on molecular approaches and the determination of relevant, virulence genes. For the future, the data from bacterial genome sequencing
may be invaluable, especially as more and more taxa are examined. The reliance on
the study of single cultures continues, data from which are diffi cult to equate with
an understanding of pathogenicity at the species level. Inter-cell communication by
quorum sensing signal molecules (= acylated homoserine lactones (AHL)) in the
regulation of some virulence factors is fascinating, with work revealing that AHLs
are produced by some Gram-negative bacterial fi sh pathogens, notably Aer. hydrophila, Aer. salmonicida, Ali. salmonicida, V. splendidus, V. vulnifi cus and Y. ruckeri
(Bruhn et al . 2005 ).
Control Measures
The development of effective disease control strategies is one aspect of bacterial fi sh
disease research that has resulted in substantial progress from new approaches to
vaccination [including genetic manipulation techniques], to the use of probiotics,
prebiotics, nonspecifi c immunostimulants and plant products. It is noteworthy that
much of this work is being carried out in less developed rather than western countries. These newer approaches have been matched by a downturn of interest in the
use of antimicrobial compounds insofar as there is increasing concern about the
development and spread of resistance and thus a reduced effi cacy against human
pathogens, and tissue residues. In many countries, there is evidence for a curb on the
use of antimicrobial compounds in all but human applications. However, it is
accepted that elsewhere antibiotics are used extensively in aquaculture, but beware
of tissue residues if the product is destined for export. In the years ahead, it is to be
envisaged that there will be ever-tighter regulations on the use of antimicrobial
compounds in aquaculture.
The Effects of Environmental Stress Including Physical
and Chemical Pollution
There is increasing concern about the possible role of pollution in disease, particularly of wild fi sh stocks (see also Pippy and Hare 1969 ; Mahoney et al. 1973 ;
Robohm et al. 1979 ). As this is a politically emotive issue, and particularly as the
impact of climate change is in the public arena, there is likely to be an increase in
monies available and, thus, a stimulation of research interest. At present, there is
considerable confusion over the precise role of pollution and fi sh health (Bucke
15 Conclusions
Pathogenicity
There has been continual interest in the determination of pathogenicity mechanisms
with current focus placed on molecular approaches and the determination of relevant, virulence genes. For the future, the data from bacterial genome sequencing
may be invaluable, especially as more and more taxa are examined. The reliance on
the study of single cultures continues, data from which are diffi cult to equate with
an understanding of pathogenicity at the species level. Inter-cell communication by
quorum sensing signal molecules (= acylated homoserine lactones (AHL)) in the
regulation of some virulence factors is fascinating, with work revealing that AHLs
are produced by some Gram-negative bacterial fi sh pathogens, notably Aer. hydrophila, Aer. salmonicida, Ali. salmonicida, V. splendidus, V. vulnifi cus and Y. ruckeri
(Bruhn et al . 2005 ).
Control Measures
The development of effective disease control strategies is one aspect of bacterial fi sh
disease research that has resulted in substantial progress from new approaches to
vaccination [including genetic manipulation techniques], to the use of probiotics,
prebiotics, nonspecifi c immunostimulants and plant products. It is noteworthy that
much of this work is being carried out in less developed rather than western countries. These newer approaches have been matched by a downturn of interest in the
use of antimicrobial compounds insofar as there is increasing concern about the
development and spread of resistance and thus a reduced effi cacy against human
pathogens, and tissue residues. In many countries, there is evidence for a curb on the
use of antimicrobial compounds in all but human applications. However, it is
accepted that elsewhere antibiotics are used extensively in aquaculture, but beware
of tissue residues if the product is destined for export. In the years ahead, it is to be
envisaged that there will be ever-tighter regulations on the use of antimicrobial
compounds in aquaculture.
The Effects of Environmental Stress Including Physical
and Chemical Pollution
There is increasing concern about the possible role of pollution in disease, particularly of wild fi sh stocks (see also Pippy and Hare 1969 ; Mahoney et al. 1973 ;
Robohm et al. 1979 ). As this is a politically emotive issue, and particularly as the
impact of climate change is in the public arena, there is likely to be an increase in
monies available and, thus, a stimulation of research interest. At present, there is
considerable confusion over the precise role of pollution and fi sh health (Bucke
15 Conclusions