481
Pathogenicity
Eels, challenged by i.p. injection with 3-day-old broth cultures, eventually displayed
the same symptoms attributed to natural outbreaks of the disease. Thus, they became
gradually inactive, and developed petechial haemorrhages prior to death, which
usually occurred in 6–10 days (Wakabayashi and Egusa 1972 ). This is a short period
for death to ensue. Of course, this depends upon the number of cells in the initial
challenge. We consider that this is indicative of the effect of exotoxins, probably
exoenzymes, although Dear ( 1985 ) could not obtain mortalities following injection
of European eels with ECP. Of course, Ps. anguilliseptica is not metabolically very
active, but most isolates attack proteins (gelatin) and lipids (Tween 80). Therefore,
it is suggested that the pathogenicity mechanism involves proteases and lipases.
There is no evidence for the presence of an extracellular layer in virulent isolates as
occurs in Aer. salmonicida. There is some evidence of species-based susceptibility
to Sekiten-byo, with Japanese eels seemingly more prone to the disease than
European eels.
It is speculative whether or not this infers that the organism may be more common in and around European eels (or may have originated with this species). A
comparative observation is that brown trout are more susceptible than rainbow trout
to furunculosis caused by Aer. salmonicida . Certainly, Ps. anguilliseptica is capable
of infecting a greater range of species than represented by the genus Anguilla . Thus,
experimental infections have been achieved in ayu, bluegill, carp, goldfi sh and loach
(Muroga et al. 1975 ). The organism is only of low pathogenicity to rainbow trout
(Lönnström et al. 1994 ).
The presence of sublethal concentrations of copper (100–250 mg/l) in water
exacerbates the disease (Mushiake et al. 1984 ). Evidence points to a reduction in
lymphocytes and granulocytes, which leads to lowered phagocytosis (Mushiake
et al. 1985 ).
Disease Control
Management Techniques Control of Sekiten-byo is possible by means of raising
the water temperature in the fi sh holding areas to 26–27 °C. By keeping the water at
this temperature for 2 weeks, followed by reducing it to approximately 21 °C, there
was no further outbreak of the disease for 5 months (Wakabayashi and Egusa 1972 ).
Vaccine Development Attempts have been made to develop formalin-inactivated
vaccines. It is encouraging that fi sh are capable of eliciting an immune response
against Ps. anguilliseptica , insofar as experimentally vaccinated eels developed
Pseudomonas anguilliseptica
Pathogenicity
Eels, challenged by i.p. injection with 3-day-old broth cultures, eventually displayed
the same symptoms attributed to natural outbreaks of the disease. Thus, they became
gradually inactive, and developed petechial haemorrhages prior to death, which
usually occurred in 6–10 days (Wakabayashi and Egusa 1972 ). This is a short period
for death to ensue. Of course, this depends upon the number of cells in the initial
challenge. We consider that this is indicative of the effect of exotoxins, probably
exoenzymes, although Dear ( 1985 ) could not obtain mortalities following injection
of European eels with ECP. Of course, Ps. anguilliseptica is not metabolically very
active, but most isolates attack proteins (gelatin) and lipids (Tween 80). Therefore,
it is suggested that the pathogenicity mechanism involves proteases and lipases.
There is no evidence for the presence of an extracellular layer in virulent isolates as
occurs in Aer. salmonicida. There is some evidence of species-based susceptibility
to Sekiten-byo, with Japanese eels seemingly more prone to the disease than
European eels.
It is speculative whether or not this infers that the organism may be more common in and around European eels (or may have originated with this species). A
comparative observation is that brown trout are more susceptible than rainbow trout
to furunculosis caused by Aer. salmonicida . Certainly, Ps. anguilliseptica is capable
of infecting a greater range of species than represented by the genus Anguilla . Thus,
experimental infections have been achieved in ayu, bluegill, carp, goldfi sh and loach
(Muroga et al. 1975 ). The organism is only of low pathogenicity to rainbow trout
(Lönnström et al. 1994 ).
The presence of sublethal concentrations of copper (100–250 mg/l) in water
exacerbates the disease (Mushiake et al. 1984 ). Evidence points to a reduction in
lymphocytes and granulocytes, which leads to lowered phagocytosis (Mushiake
et al. 1985 ).
Disease Control
Management Techniques Control of Sekiten-byo is possible by means of raising
the water temperature in the fi sh holding areas to 26–27 °C. By keeping the water at
this temperature for 2 weeks, followed by reducing it to approximately 21 °C, there
was no further outbreak of the disease for 5 months (Wakabayashi and Egusa 1972 ).
Vaccine Development Attempts have been made to develop formalin-inactivated
vaccines. It is encouraging that fi sh are capable of eliciting an immune response
against Ps. anguilliseptica , insofar as experimentally vaccinated eels developed
Pseudomonas anguilliseptica