Bacterial Diseases

1 Enteric redmouth - ERM (Yersinia ruckeri)2 Furunculosis (Aeromonas salmonicida)3 Coldwater disease – CWD (Flavobacterium

psychrophilum)4 Bacterial gill disease (Flavobacterium

branchiophila)5 Bacterial kidney disease (Renibacterium

salmoninarum)6 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•

• 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•

• 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

• From clinical signs and necropsy

• Gram negative, Rods

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• 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

• Chronic, focal dermal necrosis – BOILS

• Acute septicemia

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Clinical signs

Transmission

• Horizontal

• Dead fish/fecal material

• Mucus - asymptomatic carriers

• Sediments and associated biota

• Morphology, Stain, non-motile

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• Non spore-forming rod (1 x 2 µm)

• Pigment forming non-motile

Presumptive Diagnosis

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

• Initially described in Atlantic salmon (Scotland 1930)

• Hatchery and wild salmonids

• Global maybe except Australia, NZ ?

Bacterial Kidney DiseaseRenibacterium salmoninarum

• 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 bodyCavity, cystic cavities in skeletal muscle, etc.

Clinical signs

• 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

Diagnosis

•Erythromycin (injection of adults)• Reduce loads and transmissionIn feed• • Expensive and not approved for food fish

• No vaccines available

• Avoid infection

Control/treatment

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)