366
Epizootiology
The organism has been associated with water and the intestines of apparently
healthy fi sh (e.g. Kapperud 1981 ; Shayegani et al. 1986 ; Zamora and Enriquez
1987 ), which are likely to be the source.
Pathogenicity
It was considered that the organism was of endogenous origin, being a pathogen of
cold-stressed (possibly immunocompromised) fi sh (Carson and Schmidtke 1993 ).
Pathogenicity experiments have not been carried out.
Yersinia ruckeri
Characteristics of the Diseases
Enteric redmouth (ERM, Hagerman redmouth disease, redmouth, salmonid blood
spot) was initially diagnosed as a systemic infection among farmed rainbow trout in
the Hagerman Valley of Idaho, USA during the early 1950s, and subsequently
described in detail by Ross et al. ( 1966 ). The disease is mostly restricted to salmonids (Bullock and Snieszko 1975 ) within the geographical locations of North and
South America (Ross et al. 1966 ; Stevenson and Daly 1982 ; Bravo and Kojagura
2004 ), Denmark (Dalsgaard et al. 1984 ), Great Britain (Austin 1982 ; Roberts 1983 ),
France (Lesel et al. 1983 ), Germany (Fuhrmann et al. 1983 ), Italy (Busch 1978 ),
Ireland (McCormick and McLoughlin 1993 ), Norway (Richards and Roberts 1978 )
and Australia (Bullock et al. 1978 ; Llewellyn 1980 ). With the recent upsurge in the
number of cases of the disease, particularly in Europe, it would appear that the disease is still spreading. So far, it has been a severe problem mostly in rainbow trout,
although outbreaks of disease have been reported among populations of brown
trout, brook trout, chinook salmon and coho salmon (Dulin et al. 1976 ) and Atlantic
salmon and Pacifi c salmon (Bullock et al. 1978 ). A few non-salmonid fi sh species
have also been reported to harbour the pathogen, and these include channel catfi sh
(Danley et al. 1999 ), emerald dace ( Notropis atherinoides; Mitchum 1981 ), goldfi sh
(McArdle and Dooley-Martin 1985 ), carp (B. Austin, unpublished observation),
lake herring or cisco ( Coregonus artedii; Bullock and Anderson 1984 ), minnows
( Pimephales promelas ) (Michel et al. 1986 ) and pompano ( Trachinotus marginatus )
(Romano et al. 2012 ). Also, sea bass and turbot appear to be susceptible (Vigneulle
1990 ). In the case of rainbow trout, there is experimental evidence that signifi cantly
lower mortalities occur with increases of salinity. Thus, mortalities were reduced
from 96.5 % in freshwater to 75 % in 9‰ salinity (Altinok and Grizzle 2001a ).
Much excellent work has certainly been accomplished, but there are many basic
facets of the biology of the pathogen, which remain unknown or unclear.
6 Enterobacteriaceae Representatives
Epizootiology
The organism has been associated with water and the intestines of apparently
healthy fi sh (e.g. Kapperud 1981 ; Shayegani et al. 1986 ; Zamora and Enriquez
1987 ), which are likely to be the source.
Pathogenicity
It was considered that the organism was of endogenous origin, being a pathogen of
cold-stressed (possibly immunocompromised) fi sh (Carson and Schmidtke 1993 ).
Pathogenicity experiments have not been carried out.
Yersinia ruckeri
Characteristics of the Diseases
Enteric redmouth (ERM, Hagerman redmouth disease, redmouth, salmonid blood
spot) was initially diagnosed as a systemic infection among farmed rainbow trout in
the Hagerman Valley of Idaho, USA during the early 1950s, and subsequently
described in detail by Ross et al. ( 1966 ). The disease is mostly restricted to salmonids (Bullock and Snieszko 1975 ) within the geographical locations of North and
South America (Ross et al. 1966 ; Stevenson and Daly 1982 ; Bravo and Kojagura
2004 ), Denmark (Dalsgaard et al. 1984 ), Great Britain (Austin 1982 ; Roberts 1983 ),
France (Lesel et al. 1983 ), Germany (Fuhrmann et al. 1983 ), Italy (Busch 1978 ),
Ireland (McCormick and McLoughlin 1993 ), Norway (Richards and Roberts 1978 )
and Australia (Bullock et al. 1978 ; Llewellyn 1980 ). With the recent upsurge in the
number of cases of the disease, particularly in Europe, it would appear that the disease is still spreading. So far, it has been a severe problem mostly in rainbow trout,
although outbreaks of disease have been reported among populations of brown
trout, brook trout, chinook salmon and coho salmon (Dulin et al. 1976 ) and Atlantic
salmon and Pacifi c salmon (Bullock et al. 1978 ). A few non-salmonid fi sh species
have also been reported to harbour the pathogen, and these include channel catfi sh
(Danley et al. 1999 ), emerald dace ( Notropis atherinoides; Mitchum 1981 ), goldfi sh
(McArdle and Dooley-Martin 1985 ), carp (B. Austin, unpublished observation),
lake herring or cisco ( Coregonus artedii; Bullock and Anderson 1984 ), minnows
( Pimephales promelas ) (Michel et al. 1986 ) and pompano ( Trachinotus marginatus )
(Romano et al. 2012 ). Also, sea bass and turbot appear to be susceptible (Vigneulle
1990 ). In the case of rainbow trout, there is experimental evidence that signifi cantly
lower mortalities occur with increases of salinity. Thus, mortalities were reduced
from 96.5 % in freshwater to 75 % in 9‰ salinity (Altinok and Grizzle 2001a ).
Much excellent work has certainly been accomplished, but there are many basic
facets of the biology of the pathogen, which remain unknown or unclear.
6 Enterobacteriaceae Representatives