Bacterial Diseases of Fish

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Bacterial Diseases of Fish
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Diseases/Groups/Species Covered (fish)

• Cytophaga-like bacteria (CLBs)
• Flexibacter psychrophilus (BCWD)
• Flexibacter columnaris (columnaris disease)
• bacterial gill disease
• Enterobacteria
• Edwardsiella tarda (Edwardsiella septicemia)
• Edwardsiella ictaluri (enteric septicemia of
  catfish)
• Yersinia ruckeri (enteric redmouth disease)
• Pseudomonas fluorescens (pseudomonas septicemia)
• Aeromonas salmonicida (furunculosis)

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Shrimp Bacterial Diseases Covered

• Vibriosis
• necrotizing hepatopancreatitis
• epicommensal fouling disease

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Bacterial Coldwater Disease (BCWD)

• Serious septicemic infection of hatchery
  salmonids, especially coho salmon in Pacific NW
• first described by Davis (1946) from a single
  USFWS hatchery in West Virginia
• also known to infect catfish in Louisiana
• agent was referred to as Cytophaga
  psychrophila, now Flexibacter psychrophilus
• long slender gram negative rod, glides and flexes
• 1.5-7.5 x 0.3-0.75 µM

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Bacterial Coldwater Disease

• Culture grows well on dilute media (cytophaga
  agar or broth), yellow colonies, fried egg
  appearance, optimum temp 15oC
• Epizootiology affects young fish of all
  salmonids, mainly in U.S., also in France
• reservoirs are infected and carrier fish, normal
  member of fish body surface
• transmission horizontal (requires lesion),
  vertical (adult--gteggs--gtoffspring) common on egg
  surface

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Bacterial Coldwater Disease

• Environmental Factors occurs at low temps
  (7-10), losses drop as temp rises, mortality
  greatest in early fry stages (30-50), compounded
  by crowding, organics, high flow rate
• Pathology external lesions on fins, skin,
  muscle, saddle lesion near dorsal, caudal
  sometimes destroyed darkening spinal
  deformities
• Diagnosis presumptive via micro for gram
  negatives in lesion, growth on cytophaga agar
  confirmatory serological

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Bacterial Coldwater Disease

• Control prevention only via avoidance, no
  vaccines available treatment via prophylactic
  drugs (e.g., formalin)
• Therapy external treatment, oxytetracycline
  (10-15 mg/L), quarternary ammonium (2 mg/L) as
  dips internal treatment with nifurpirinol (not
  approved) as absorbed thru skin, oxytet in feed
  at 50-75 mg/kg/fish/day for 10 days

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Bacterial Coldwater Disease
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Columnaris Disease

• Disease is so named because it produces mounds or
  columns in wet mounts, characterized by extensive
  erosion of the skin and gills
• originally described by Davis (1922) from
  Mississippi River
• Agent Flexibacter columnaris or Cytophaga sp.
• morphology long, thin, gram negative,
  aggregates in mounds on slides

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Columnaris Disease

• culture same as BCWD
• Epizootiology 36 different species, salmonids
  and catfish most significant, highly virulent due
  to temperature, creation of dams, crowded
  elevators, largest fish kill recorded (14 M)
  associated with it
• reservoirs wild fish, typically suckers, normal
  denizen of mucous, long-term life span
• transmission horizontal, water, experimental
  via moribund carcasses
• pathogenesis acute, chronic or carrier
  dependent on strain virulence, temp, stress

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Columnaris Disease

• environmental factors elevated temps, temp
  depends on host species, usually gt15oC, severity
  increases with temp, high pH, hard water, organic
  matter, cleanliness important, crowding
• Pathology lesions confined to head, back,
  gills, starts as raised whitish spots distal on
  fins, gills
• gradually develops into large ulcers, bacteria
  isolated from leading edge of ulcer
• skin eventually erodes away, exposing muscle
• death rapid if necrosis/lesions are on gills due
  to respiratory problems
• highly virulent strains cause death w/out lesions

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Columnaris Disease

• Diagnosis presumptive via observance of long,
  thin gram negative rods from lesions rhizoid
  colonies on cytophaga agar haystacking, clinical
  signs
• confirmatory serological tests
• Control improved environment, cooler water
  temp, increased oxygenation, decreased crowding,
  organics, reduced stress
• Therapy internal via oxytet in feed,
  sulfonamides, nifurpirinol external as Roccal or
  Hyamine (benzalkonium chloride), diquat, some
  success with immunization

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Bacterial Columnaris Disease
Rhizoid colonies
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Bacterial Gill Disease (BGD)

• Affects hatchery-reared salmonids, cytophagal
  bacteria in gill lamellae, high level production
  of mucous
• Agent etiology not well agreed upon, could be
  caused by high levels of organics irritating
  secondary lamellae, mucous then colonized by
  bacteria
• probably Flavobacterium branchiophila
• morphology variety of cytophagal-type bacteria
  thus, morphology variable as gram negative rods
  to filaments
• culture cytophaga agar, as F. branchiophila, it
  shows round, smooth transparent colonies, 5-30oC

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Bacterial Gill Disease (BGD)

• Epizootiology wide range of hosts, salmonids
  mainly, occurs in warmwater fish, but not same
  bacteria yearlings and older salmonids less
  susceptible than fry mainly a U.S. problem
• reservoirs not clear, probably infected fish,
  mud, silt in water
• transmission not clearly demonstrated, probably
  from other fish
• environmental factors poor water quality,
  crowding, high organics, suspended solids, stress
  as unfavorable temps

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Bacterial Gill Disease (BGD)

• Pathology loss of appetite, cant orient with
  current, elevated respiratory rate
• gill lamellae show proliferation of epithelial
  mucous, advanced cases show clubbing and fusing
  of lamellae, cotton-like tufts extending from
  opercula
• Presumptive Diagnosis large numbers of long
  filamentous bacteria, swollen gills, fused
  filaments, clinical signs
• Confirmatory Diagnosis non available

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Bacterial Gill Disease (BGD)

• Prevention good environment water free of
  adult fish, silt, mud no crowding (most
  significant factor) strict hygiene
• Treatment successful treatment depends upon
  severity of problem (easy to kill by
  overtreatment) quarternary ammonium compounds,
  chloramine T, oxytetracycline salt _at_1-5 for 1-2
  min extremely effective

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Bacterial Gill Disease
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Edwardsiella Septicemia (EPDC)

• Disease associated with Edwardsiella tarda, a
  member of the enterobacteria
• all are gram-negative, facultative aerobes,
  moving via use of flagella, catalase positive,
  cytochrome oxidase negative
• pathogen of or can be carried by many vertebrates
  and invertebrates (large reservoir)
• can produce gastroenteritis in humans

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Edwardsiella Septicemia (EPDC)

• Agent gram negative rod, motile by flagella,
  grows well on most standard media (TSA, BHI),
  produces small transparent and smooth circular
  colonies _at_ 35oC
• ferments glucose and produces gas, indole
  positive (dif. from E. ictaluri)
• Epizootiology southern U.S., SE Asia, Pacific
  NW, many warmwater species of fish (mainly
  channel cats and bullheads), can infect other
  homeotherms and poikilotherms

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Edwardsiella Septicemia

• reservoirs water (75), mud (64), many natural
  hosts
• transmission probably horizontal, host to host
• pathogenesis fish large than 38 cm (high
  value), slow progress, low mortality unless fish
  stressed (5--gt50 mort), causes development of
  gas filled abscesses containing sulfide
• environmental factors higher than 30oC water,
  organics, crowding salmonids _at_ temps greater
  than 200C

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Edwardsiella Septicemia

• Pathology mild infections exhibit small
  cutaneous postlateral lesions, progressing as
  abscesses in muscles of flank or caudal peduncle,
  lose control of posterior portion of body
• Diagnosis isolation from kidney into TSA or
  BHI presumptive as gram negative, motile rod,
  cytox neg confirmation serological
• Control good culture environment, oxytet at 2.5
  g/45kg feed/fish/day for 10 days, some vaccine
  work, but only on eels in Japan

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Edwardsiella septicemia