Transcript INFECTIOUS COMMON FISH BACTERIAL PATHOGENS

Bacterial Diseases
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Enteric redmouth - ERM (Yersinia ruckeri)
Furunculosis (Aeromonas salmonicida)
Coldwater disease – CWD (Flavobacterium
psychrophilum)
Bacterial gill disease (Flavobacterium
branchiophila)
Bacterial kidney disease (Renibacterium
salmoninarum)
Strawberry disease
Yersinia ruckeri
• Enteric Redmouth Disease (ERM)
• “Hagerman Redmouth” primarily RBT
• Rucker - First reported in 1958 in
Hagerman Valley. Named in 1978
Yersinia ruckeri
Host Range and Vectors
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• North American outbreaks – possibly due to
carrier fish or contaminated eggs from Idaho
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• Sources - imported baitfish, ornamentals, bird
feces, etc.
Clinical Signs ERM
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• Chronic:
• Reddening in mouth and under
operculum, and internally throughout
peritoneum, intestine, and fat of the body
Y. ruckeri
• Obligate parasite
• Generally occurs 13° - 15°C
• Acute, sub acute, chronic forms
Yersinia ruckeri
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• Non-spore forming, straight rod
• Motile with flagella
• No pigment, grows slowly at 8 and 35.
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Carrier State
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• Intestinal shedding of organism
• Stress conditions, carriers transmitted Y.r.
to healthy fish but unstressed fish did not
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Virulence of Y.r.
• Strain typing has been done widely
(Hagerman – Type I)
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Treatment and control
Vaccines:
• First were Ross and Klontz 1965. JFRBC
22:713-719. phenol killed (in feed)
• First commercial fish vaccine: licensed by
USDA in 1976 (formalin-killed whole cells)
• Single most effective management tool for
control of mortality due to ERM.
Coldwater Disease
Flavobacterium psychrophilium
• Bacterial cold-water disease - CWD
• First observed in Leetown WV in
rainbow (peduncle disease)
• Next in 1948 in Washington - lesions near
tail, and on dorsum
Host Range and Vectors
• Serious infections in salmonids
worldwide - distributed widely across NA
continent
• Has been linked to viral pathogens such
as IHNV
Host Range and Vectors
• Free-living examples exist
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• Resident salmonids likely carriers
Clinical Signs CWD
• Externally: rough appearance of skin and
necrosis of fins
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• May see open ulcerations on skin
• External or septicemic
Clinical Signs CWD
• Internally:
• Erratic/spiral swimming
• Development of deformities and/or
nervous disorders
Transmission
• Natural reservoirs uncertain
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• Mortalities increase when IHN involved
• Number one concern in Hagerman Valley
Diagnosis of CWD
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From clinical signs and necropsy
Gram negative, Rods
Gliding motility
Growth best on low nutrient media
Treatment and control
• Extra-label use of antibiotics for control –
somewhat effective (but resistance a
potential problem)
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• Vaccines
Furunculosis
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• One of the oldest known bacterial fish
pathogens
• Mostly associated with salmonids, but other
fish can be infected
• Obligate pathogen (fish to fish transmission)
Clinical signs
• Acute - Adult, sub-adult, darken, stop
feeding, hemorrhage base fins, internal
hemorrhages
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• Fingerlings - dark, dying
Clinical signs
• Chronic, focal dermal necrosis – BOILS
• Acute septicemia
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Transmission
• Horizontal
• Dead fish/fecal material
• Mucus - asymptomatic carriers
• Sediments and associated biota
Presumptive Diagnosis
• Morphology, Stain, non-motile
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• Non spore-forming rod (1 x 2 µm)
• Pigment forming non-motile
Treatment and control
Antibiotics:
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• Resistance can be a problem
Vaccines:
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Bacterial/environmental Gill Disease
(Flavobacterium branchiophilum)
• Gill infections primarily in juvenile fish
• F. branchiophilum dominant bacterial
species
• Found throughout North America and
other countries
Clinical signs BGD
• Flared gills, lethargy, swim high in water
column
• Gill lamellae fused/clubbed (poor oxygen
transport)
• Debris and bacteria present
• Usually associated with poor environmental
conditions or parasitic infestation
Diagnosis/control
Diagnosis:
• Usually based on clinical signs (obvious)
• Test for specific bacteria
Control:
• Improve environmental conditions (increase
DO)
• Treat fish (various chemicals), 1-5% NaCl may
be method of choice
Bacterial Kidney Disease
Renibacterium salmoninarum
• Initially described in Atlantic salmon
(Scotland 1930)
• Hatchery and wild salmonids
• Global maybe except Australia, NZ ?
Clinical signs
• Systemic infection slowly progressive
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• Acute and chronic forms
• External: exophthalmia, blood filled blisters
on skin, pale gills, etc.
• Internal: multifocal grey-white nodules on
kidney and other organs, cloudy fluid in body
Cavity, cystic cavities in skeletal muscle, etc.
Diagnosis
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Gram Positive Fish Pathogen
0.5 X 1 µm pairs or short chains
Requires L-cystein
Serum or blood enhances growth
Slow growing - 20 - 60 d
Survives inside phagocytic cells
FAT/ELISA
Clinical signs/exam
Control/treatment
•Erythromycin (injection of adults)
• Reduce loads and transmission
In feed
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• Expensive and not approved for food fish
• No vaccines available
• Avoid infection
Disease of unknown etiology
• Strawberry disease
– Symptoms
• Reddened raised inflammation on skin
• Morbidity 10-15%
• Market size fish affected
– Cause
• Bacterial (?)
• Allergic reaction (?)
– Treatment
• Antibiotics (withdrawal period)