242
monicida , compared with 31 positives achieved by culturing the mucus, and 16
positives by culturing the organs (Quinn and Stevenson 2012 ).
Epizootiology
The Ecology of Aeromonas salmonicida McCarthy ( 1980 ) performed detailed
experiments concerned with the ecology of Aer. salmonicida and also reviewed the
work carried out by others. According to his report, contact with infected fi sh or
contaminated water and fi sh farm materials, and transovarian transmission have all
been cited as probable routes of infection. Also, carrier fi sh, which show no overt
signs of disease but harbour the pathogen in their tissues, appear to be implicated in
horizontal or vertical transmission. Such carrier fi sh are presumed to provide a reservoir which retains the pathogen in fi sh populations. Sea lamprey have been found
to harbour typical Aer. salmonicida , and it may well be that this fi sh species is a
possible source of infection for salmonids (El Morabit et al. 2004 ).
To understand how Aer. salmonicida is transmitted both among and within fi sh
populations it is necessary to know the source of the pathogen and its capacity to
survive in the environment. In fact, most of the work done on epizootiological
aspects of fi sh diseases caused by Aer. salmonicida has focused on investigations of
potential sources of infection. The role of water, mud and detritus, contaminated
implements on fi sh farms, animals other than fi sh themselves, and particularly, carrier fi sh, (i.e. salmonids as well as non-salmonids) as potential sources of infection
with Aer. salmonicida have been examined. The popular approach to the study of
this subject has been to determine the presence of and survival capabilities of Aer.
salmonicida in the variety of habitats listed above. Certainly, there is evidence that
the pathogen can survive without a signifi cant change in numbers in transport systems, such as containing Stuart’s medium, at 18–20 °C for 48 h (Cipriano and
Bullock 2001 ). This opens up the possibility of transporting samples from fi eld to
laboratory without greatly infl uencing the populations of Aer. salmonicida.
Aeromonas salmonicida – Survival Studies The survival of Aer. salmonicida in
water has been thoroughly examined by numerous investigators (Williamson 1929 ;
Smith 1962 ; Lund 1967 ; McCarthy 1980 ; Sakai 1986a , b ; Rose et al. 1990a , b ;
Morgan et al. 1991 ; Effendi and Austin 1991 , 1994 ; Table 5.2 ). Unfortunately, caution must be used in the interpretation of some of the data as many of the studies
employed pre-sterilised water or types of water in which Aer. salmonicida would
not normally be present, e.g. distilled or tap water. Thus, the information gleaned
from such studies does not necessarily refl ect the behaviour of the pathogen in the
natural aquatic environment. However, enough work has been done to allow tentative conclusions to be drawn. Based on the survival data accumulated, it appears that
Aer. salmonicida is capable of surviving for a prolonged period in fresh, brackish
and sea water, although contradictory results as to the exact time interval involved
abound. Thus for unsterilised fresh water, including river water, recovery of the
5 Aeromonadaceae Representative (Aeromonas salmonicida)
monicida , compared with 31 positives achieved by culturing the mucus, and 16
positives by culturing the organs (Quinn and Stevenson 2012 ).
Epizootiology
The Ecology of Aeromonas salmonicida McCarthy ( 1980 ) performed detailed
experiments concerned with the ecology of Aer. salmonicida and also reviewed the
work carried out by others. According to his report, contact with infected fi sh or
contaminated water and fi sh farm materials, and transovarian transmission have all
been cited as probable routes of infection. Also, carrier fi sh, which show no overt
signs of disease but harbour the pathogen in their tissues, appear to be implicated in
horizontal or vertical transmission. Such carrier fi sh are presumed to provide a reservoir which retains the pathogen in fi sh populations. Sea lamprey have been found
to harbour typical Aer. salmonicida , and it may well be that this fi sh species is a
possible source of infection for salmonids (El Morabit et al. 2004 ).
To understand how Aer. salmonicida is transmitted both among and within fi sh
populations it is necessary to know the source of the pathogen and its capacity to
survive in the environment. In fact, most of the work done on epizootiological
aspects of fi sh diseases caused by Aer. salmonicida has focused on investigations of
potential sources of infection. The role of water, mud and detritus, contaminated
implements on fi sh farms, animals other than fi sh themselves, and particularly, carrier fi sh, (i.e. salmonids as well as non-salmonids) as potential sources of infection
with Aer. salmonicida have been examined. The popular approach to the study of
this subject has been to determine the presence of and survival capabilities of Aer.
salmonicida in the variety of habitats listed above. Certainly, there is evidence that
the pathogen can survive without a signifi cant change in numbers in transport systems, such as containing Stuart’s medium, at 18–20 °C for 48 h (Cipriano and
Bullock 2001 ). This opens up the possibility of transporting samples from fi eld to
laboratory without greatly infl uencing the populations of Aer. salmonicida.
Aeromonas salmonicida – Survival Studies The survival of Aer. salmonicida in
water has been thoroughly examined by numerous investigators (Williamson 1929 ;
Smith 1962 ; Lund 1967 ; McCarthy 1980 ; Sakai 1986a , b ; Rose et al. 1990a , b ;
Morgan et al. 1991 ; Effendi and Austin 1991 , 1994 ; Table 5.2 ). Unfortunately, caution must be used in the interpretation of some of the data as many of the studies
employed pre-sterilised water or types of water in which Aer. salmonicida would
not normally be present, e.g. distilled or tap water. Thus, the information gleaned
from such studies does not necessarily refl ect the behaviour of the pathogen in the
natural aquatic environment. However, enough work has been done to allow tentative conclusions to be drawn. Based on the survival data accumulated, it appears that
Aer. salmonicida is capable of surviving for a prolonged period in fresh, brackish
and sea water, although contradictory results as to the exact time interval involved
abound. Thus for unsterilised fresh water, including river water, recovery of the
5 Aeromonadaceae Representative (Aeromonas salmonicida)