APBI - M2 L3

Vibrio anguillarum

Vibriosis

also Vibrio ordalii

Vibrio samonicida

Cold Water Vibriosis or Hitra Disease

Aeromonas salmonicida

var. salmonicida

Furunculosis

Atypical furunculosis

A. salmonicida var. achromogenes/nova

Flexibacter spp.

Bacterial Gill Disease complex and fin-rot

Yersinia ruckeri

Enteric redmouth disease

Aeromonas hydrophila

Pseudomonas spp.

Opportune septicaemia

Piscirickettsia spp.

Rickettsial septicaemia (intracellular bacteria)

Renibacterium salmoninarum

Bacterial Kidney Disease

BKD

• caused by small Gram-positive diplobacillus called Renibacterium salmoniarum)

  • is restricted to salmonids (Pacific + Atlantic species, trout, charrs)

 

• widely distributed in almost all countries where salmon are present except Australia and New Zealand

• diagnosed in feral salmon in fresh + salt water

• mortality rates:

  • vary seasonally, spring and fall usually

  • but they occur all year

• transmitted vertically @ spawning and horizontally within net pens / hatchery troughs

• generally chronic

• hard to culture them so use IFAT

• white swellings on spleen, liver, heart, kidney, peritoneal surfaces

• also maybe exophthalmus

Tuberculosis

• Fish T.B caused by orgs from genus Mycobacterium -- disease often called mycobacteriosis

  • actual bugs involved: Mycobacterium marinum + Mycobacterium fortuitum

  • = different species from relatives that cause TB in humans and other terrestrial vertebrates

 

• Fish mycobacteria can cause localized infections in human skin cuts --> leads to condition called aquarist's finger

  • if not treated can become serious health concern

 

Mycobacteriosis

• most significant bacterial infection of ornamental warm water aquarium fish

  • present @ low level of infection in many tanks

  • significant problem in west coast hatcher-reared salmonids that were fed diet of ground scrap fish

  • problem fixed when diet switched to pasteurized or processed food

  • not readily treated and the usual cause is overcrowding and poor water quality

has been cultured in swimming pools, beaches, natural streams, estuaries, tropical fish tanks, city tap water

can infect humans

• Externally:

  • exophthalmia

  • enlarged abdomen (dropsy)

  • protruding scales (edema)

 

• Internally:

  • large numbers of small gray / white nodules in liver, kidney, heart, spleen

  • maybe skeletal deformities

 

• lethargy

• anorexia

• fin + scale loss

• emaciation

• skin inflammation + ulceration

• peritonitis

• nodules in muscles that can deform fish

• gram-positive

• rods varying in size that're nonmotile

• acid-fast

• on solid media: solid cream-coloured to yellow colonies

 

Furunculosis

• comes from red, raised areas appearing on skin in some infected fihs; look like hair follicle abscesses of mammals called furuncles

• One of first bacterial diseases of fish identified when described 19th century Europe brown trout

  • can happen in salmonids and non-salmonids but brook trout particularly susceptible

 Externally: signs typical are seen in all Gram-negative septicemia's

• may darken and stop feeding

• may haemorrhage at base of find + have swollen and haemorhagic anus

  • haemorrhage around mouth and raised red patches / ulceration on skin

 Internally:

• spleen often large, soft + bloody

• kidney swollen, soft, and haemorrhagic

• muscle necrosis common

• cross section of muscle cut beneath red skin patches reveals large red, liquid zone of dead muscle tissue

Diagnose by gram staining smear of kidney and culturing on TSA

 

Piscirickettsia

Aka salmonid reckettsial septicemia (SRS), coho salmon septicemia, Huito disease

• fastidious so doesn't grown on known artificial media, must be grown in tissue culture

primarily reported in farmed marine fish and observed in salmonids from freshwater facilities

• transmission mechanisms not understood fully

 small white lesions or shallow haemorrhagic ulcers on skin

• Dark

• Lethargic

• Will collect along sides of netpen

 Major gross pathological changes:

• gill pallor (pale gills)

• peritonitis (inflammation of the peritoneum)

• ascites (abdominal fluid accumulation)

• enlarged spleen

• swollen grey kidney

• liver w/ large pale necrotic lesions

Sensitive to antibiotics so shouldn’t be used in media during tissue collection for culturing

Doesn’t grow on artificial bacteriological media

Diagjose with cell culture and Giemsa stained tissue impressions

Motile Aeromonas Septicaemia (MAS)

Aeromonas hydrophila = motile, non-pigmented cousin to A.salmonicida

• Internal + external signs typical of other Gram-negative septicemias 

• Can be confused with Pseudomonas fluorescens ; it produces almost identical disease

  • best distinguished by culturing bacterium from spleen and kidney of diseased fish

Diagnosticians look for other primary invaders and inciting stressors when disease is diagnosed because not typically the primary pathogen

• considered more of an opportunistic environmental pathogen

 

• There's a epidemic of wild and farmed fish in SE Asia called Epizootic Ulcerative Syndrome that's associated w/ several A. hydrophila subtypes and other infectious agents

 can cause issues in humans

• cuts and scrapes can allow entry point; preference for high temps means it can lead to infection

 

Enteric Redmouth (ERM)

• reddening of head and mouth in young salmonids in fresh water

  • problem for rainbow trout growers in some regions 

• Diagnosis can't be confirmed by head and mouth reddening alone; that can also be seen in other Gram-negative septicemias and might not appear in ERM disease

• Clinical external + internal signs + transmission similar to those described for furunculosis

• Organisms can be isolated from environment and from carrier fish

• Immersion vaccines looking effective

Vibriosis

Vibrio spp.

• Important disease of farmed marine salmonids in BC

  • might be caused by more than 1 species of bacteria

 first seen in eels

• usually (but not exclusively) restricted to fish in salt water

  • outbreaks usually in summer; particularly smolts in their first summer in seawater

  • occasional mortalities year round

• Large haemorrhages in liver

• Peritoneal petechia - red or purple spots of haemorrhage on lining of abdominal cavity

• Soft bloody spleen

• Diagnosis:

  • by Gram stain

  • culture of kidney and spleen smears

• on stained smears: slightly curved appearance but that's not enough to confirm diagnosis

• motile org, grows well on standard bacteriological media @ room temp if supplemented w/ salt @ about 1%

• Cultures can be presumptively classified as V. anguillarum / V. ordalii using specific immunological slide agglutination tests

• Smoothing stress predisposes fish to develop this

• Dip vaccines effective

 

Flavobacteria

• Reclassified several times

  • aka Chondrococcus, Cytophaga, Myxobacteria

• All Gram-negative, rod shaped bacteria w/ unusual gliding motion on solid surfaces

• Associated w/ mucous surfaces; often referred to as Myxobacteria

 1. Flavobacterium branchiophilum - Bacterial gill disease

2. Flavobacterium columnare - Columnaris disease

3. Flavobacterium psychrophilum - Coldwater (peduncle) disease

Bacterial gill disease

Flavobacterium branchiophilum

• Disease of significant worldwide economic importance in salmonid hatcheries

• Can occur across wide range of temps but tends to affect mainly young fish, so often observed during cooler spring temps

• Affected fish visibly distressed

  • flared opercula

  • rapid opercular movements

• Inspecting externally, gill filaments pale and clubbed (stuck tgt)

• Rapid diagnostic technique: examination of gill wet mount under microscope

  • will show increased mucous

  • hyperplasia (increased cell numbers) of lamellar epithelium

  • fusion of adjacent lamellae

  • clumps of filamentous bacteria adhered to surface of gills

    • seen on Gram stained smear of gill tissue

• Most seen in spring

• Bacteria attaches to gill tissue → form clumps → reproduce forming surface mat → gill lamellar tip fusion occurs → hyperplasia of epithelial cells

  • fungi can become secondary invaders on damaged gills of fish that survive initial disease

Columnaris disease

Flavobacterium columnare

• Long, slender, flexible, filamentous, Gram-negative bacterial rods

  • members of group (includes pathogenic bacteria) can be isolated from mucous on normal fish skin

• diseases tend to affect body mucous surfaces; gills + skin !

• can occur in wide variety of fresh water and aquarium fish

• appears as saddle-shaped white region around dorsal fin

• shade comes from death and shedding of epidermal cells in area → exposes pale, fibrous compact dermis

• Gills + mouth can also be affected

  • death of tissues around mouth (necrotic stomatitis)

• Usually seen in warmer water + when there's increased organic matter in water following overfeeding 

• Tentative diagnosis made by observing large numbers of filamentous bacteria on wet moutns or Gram stains of skin smears → then confirmed by culture

  • culture requires special low nutrient medium

 

Cold water peduncle disease

Flavobacterium psychrophilum

• Condition usually seen at lower water temps (less than 8)

• Predisposed by high stocking densities and increased org matter in water

  • mostly restricted to salmonids in N hemisphere

• Externally:

  • erosion of fins and tail

    • sometimes total

  • covered by cottony growth of fungus

• Can lead to high mortalities

• Diagnosis: same as with columnaris

  • culture might be more successful if plates incubated at cooler temps

• Affected fish might recover → develop chronic infection

• Can transmit both horizontally and vertically