APBI 419 - Module 2

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

Pharmacology

• study of drugs and chemicals on living systems

  • basis of treatments

Therapeutic treatments

• those that’re applied after a problem has occurred; reactive treatments

• Chemicals applied in preventive manner

•  usually directed against bacterial and/or parasitic diseases brought about by stress

  • main application = form of application (metabolic products of microorganisms) designed to inhibit or kill competing bacteria

  • some broad spectrum and active against many bacteria others not so much and only inhibit few species

 Drugs don’t often eliminate infectious organism

Keep applying antibiotics even if fish look better

Antibiotics

• substances that kill or inhibit bacterial growth

  • may be natural products of microorganisms (bacterial, fungi), semi-modifications, or fully synthetic compounds

  • competitive factors

• don’t kill viruses

Resistance development in face of selection pressures

• bacterial capacity to adapt to external changes using these mechanisms

  • developing resistance lets resistant orgs to proliferate in prevailing conditions

Inherent/intrinsic resistance

species not normally susceptible to particular drug

• could be due to inability of antibacterial agent to enter bacterial and reach target site

• or lack of affinity between antibacterial and its target (site of action)

• or absence of target in the cell

Acquired resistance

• when bacterial species normally susceptible to particular drug but certain strains express drug resistance

  • after resistance develops, antibiotic not able to cure or treat disease caused by infective agent

  • low level resistance might be detected by slight increase in minimal inhibitory concentration (MIC) for antibiotic from usual value (not necessary of clinical significance)

  • higher degree of resistance characterized by MIC that exceeds concentrations of drug safely attainable in patients tissues

Plasmid acquisition

2 basic mechanisms for development of antibiotic resistance in microbes

• accounts for enzymes that inactivate the antibiotic, or titration, by over-production of target enzyme

• resistance genes carried on R plasmids

• plasmids replicate independently of bacteria's genomic DNA; circular

• inheritance of resistance from plasmid = exogenous inheritance since resistance genes on R plasmids have diff base comp from corresponding genes in host

Chromosomal mutant

2 basic mechanisms for development of antibiotic resistance in microbes

• resistance acquired by mutation results in altering of target site most of time

• changing protein's structure by chromosomal mutation → changes conformation of target site → antibiotic doesn't bind

• might also result in decreased permeability to antibiotic

• mutations allow resistance to one antibiotic / closely related antibiotics cuz structure of specific protein = altered

Conjugation

• how plasmids are transmitted between bacteria

  • one way transfer of genetic info

  • not species-specific

  • many diff species of bacteria share similar resistance methods

Transposons

• discrete genetic units that translocate from one bacterial genome to another

  • incapable of autonomous replication; unlike plasmids

  • have special sequences @ terminals → can integrate into other strands of DNA (transposition)

• Plasmids can obtain new resistance genes by this

 

Gene cassettes

• plasmids can also acquire resistance genes from these

  • they encode specific resistance gene

  • integrons have to provide receptor site for them + enzyme that catalyzes mobility of gene

 

Prophylactic treatments

designed to prevent disease outbreaks through vaccination, biosecurity, and management practices

• use is usually discouraged due to resistance concerns

• prop vaccination + improved husbandry = essential prevention tactics

Multivalent vaccines

• one vaccine can provide protection against number of diff pathogens

  • many contain compounds called adjuvants or immunomodulators

  • compounds supposed to start body's production of protective molecs and might help fish defend fish itself against other pathogens that vaccine not specifically designed to combat

Killed vaccines

• vaccines where chemicals, or heat, used to kill but not destroy pathogen; commonly called bacterins

  • most on market today = bacterins made from cultures of disease agents grown under specific conditions then killed

  • leaves external structure intact so that they stimulate immune system to produce protective antibodies and maintain memory of agent

  • doesn't cause disease and can't replicate

Attenuated vaccines

• v effective; pathogen alive and viable, weakened, can't cause disease

  • it will infect fish and reproduce sufficiently enough to stimulate immune system

  • concern: it could revert to virulent state so pause on development for fish cultures

Sub-unit and DNA vaccines

• expose fish to parts of the pathogen that incite immune response 

  • made by growing infectious organism → ID-ing external surface responsible for stimulating protective immune response → using genetic engineering to produce another org that has same external structure on its surface

  • that engineered org can be used to make a bacterin

  • can apply the DNA that codes for the imp antigens

Immersion treatments

• strong concentration of chemotherapeutant used for short period of time

• fish suspended in aerated container of solution

• exposure varies with treatment but don't generally last more than few minutes

• duration short, but make sure container with therapeutics is aerated

• they need more oxygen when stressed; and container is probably at lower conc than enclosure they just came out of

• make sure water is same temp

• water for anaesthetic and treatment baths should come from same enclosure as fish you're treating

 

Spraying

• exposed skin, mucus, potentially gills sprayed w/ vaccine

  • somewhat stressful for fish

Rapid flush

• strong conc of chemical flushed through treatment system

• treatment duration = length of time it takes to completely replace water in trough, tank, incubator

• entire chemical added at once; moves through unit as water is exchanged

 

Bath method

• is longer than dip or rapid flush

  • required amount of chemical added and remains for prescribed length of time

  • ensure chemical is adequately mixed in treatment unit

• prolonged + indefinite variety

• should be observed continuously during treatment

• if distress seen, untreated water should be added quickly and chemical flushed out

• use aerators in tanks during treatment to maintain adequate oxygen supply

Prolonged variety

type of bath method; where chemical is rapidly flushed from system after specific timeframe

Indefinite variety

type of bath method; chemical allowed to dissipate or disintegrate naturally

Chloramine-T

• useful surface anti-parasitic and antibacterial treatment usually as bath treatment @ 10-20 mg/L between 1 hr - 3 days

  • dose depends on use, pH and water hardness

  • shouldn't be used as high dose dip treatment

    • chemical action will cause serious damage to fish

  • may also be dangerous to person

    • wear mask and goggles when handling to prevent injury to skin or eyes

Injections

• Not really viable unless small numbers of valuable fish or broodstock

 

• Fish have to be anaesthetized fully minimize handling stress + ease of injection

  • fish weighed and vol of required drug then calculated and injected either intramuscular or intra-peritoneal (into body cavity)

  • dorsal sinus injection was also a common method in the past; needle isn't inserted long enough for treatment to permeate, so most follows needle out of fish

Intraperitoneal Injection (IP)

used in fish particularly farmed salmonids

• Peritoneal cavity = easy access to deposit medications and vaccines

  • this way rapid uptake of compounds into systemic circulation of fish

• Oil added to IP-injected vaccines to delay antigen release

•  safe and fast process

Dorsal sinus injections (DS)

drugs placed connective tissue lined sinus between back muscles of fish

• Technique og developed to deliver erythromycin to broodstock cuz antibiotic caused muscle necrosis and absorbed too rapidly is intramuscularly injected

•  hit exact midline and proper depth; if needle not left in for short period following injection, much of injected compound often follows needle as drawn out

Intramuscular injections (IM)

Not commonly used method of injection

• Several sites that can be injected:

  • midway between dorsal fin and lateral line (midline dorsal site)

  • musculature of peduncle or flank (towards tail)

  • pectoral fin muscles

• Not practical w/ small fish; lacks muscle

Cell degeneration

due to cell membrane injury by bacterial action → fluid can't kept out → swelling

• if damage bad → rupture →  die aka necrosis

How cells can adapt to injury

1. atrophy: shrinking

2. hypertrophy: growing

3. hyperplasia: multiplying

4. neoplasia: uncontrolled multiplication

5. metaplasia: changing form

Mutualistic

• host and microbe benefit

  • ex. skin + intestinal tract have populations of bugs

Infectious relationship

• when bug can colonize and reproduce on/in host

  • elicits host response

  • ex. normal flora can become pathogenic; normally non-pathogenic bugs can become so in an immunocompromised host

Opportunistic pathogen

might require host tissues during its life cycle; not generally associated w/ disease unless in unusual location or host

Obligate pathogen

• must have host to survive and depends on host for survival

  • when in host, pathogens generally elicit disease response

Facultative pathogen

can survive outside a host and infect them

Carriers

• w/ both asymptomatic + sub-clinical infections, proportion of pop can carry

• danger = not showing signs of disease but can be exposing and infecting others w/ dangerous pathogens

Pathology

• scientific study of nature of disease and its causes, processes, development, and consequences

  • clinical pathology = study of samples taken usually from living animals

    • you examine the samples w/ respect to their cellular constituents or chemical constituents

    • can provide you w/ info in assessing health status of fish

    • helps in detecting + predicting problems that haven't shown characteristic disease signs

Hypoxia

•  loss of ability to carry on sufficient aerobic oxidative respiration

  • most common cause of cell injury and death

• cause: ischemia

• local causes:

  • blockage of arteries that bring in fresh blood

  • any blockage of veins that let blood leave; fresh blood can't flow in

  • shunting of arterial blood other places

• systemic: failure of heart to pump enough blood

Ischemia

loss of arterial blood flow

Hypoxaemia

when blood is too low in oxygen

• ex:

  • heart can't pump enough blood through gills

  • reduced O₂-carrying capacity of blood (anaemic hypoxia)

  • haemoglobin problems

Acute inflammation

response to recent or ongoing injury

• features:

  • dilatation

  • leaking of vessels

  • involvement of neutrophils - circulating immune cells

Chronic inflammation

late-phase inflammation + response to prolonged problems

• features:

  • infiltration of more cells

  • presence of fibrin

Inflammation

Common response to most infections

• noxious, non-infectious things can also produce this

Signs:

• swelling

• redness

• fluids in tissues or cavities

• fibrin coatings

• granulomas

• pus

Granulomas

swollen, irregular/bumpy, white-yellow nodules

Fibrin

insoluble protein essential to clotting of blood, derived from fibrinogen; released from damaged vessels

• activated by clotting cascades when blood meets tissue fluids

• forms meshwork that controls bleeding, walls off stuff, then becomes framework that'll form scar

• appearance: white, lacy material (ex. BKD)

  • BKD causes ___ deposits; it will appear as white lacy enveloping organs

• can be reabsorbed, or form adhesions (after vaccinations)

Pus

fluid product of inflammation that has liquid containing leucocytes and debris of dead cells and tissue elements liquefied by proteolytic enzymes

Ascites

 fluid in abdominal cavity

Edema

excess fluid between cells

Leaky vessels

problem w/ fluids and blood movement

• caused by microbes or toxins

  • blood leaking from vessels

  • signs of vessel damage in certain infections + some nutritional problems

Necrosis

 cells swell and break open, release content, and can damage neighbouring cells → provoke inflammation

Pressure problems

problem w/ fluids and blood movement

• if can't get rid of excess fluid →  excretion problems (gills, kidneys)

• osmotic stress

• pump and vessel problems

Autolysis

• dead cell being self-digested by lysosomal enzymes

  • is temperature dependent and varies with cause

  • if seeing all kinds of dead tissue →  likely this

  • gills = good indicator

Malformation

• when smth wrong before birth

  • deformities depend on when animal is affected in development

    • range from embryonic death - subtle, internal anatomic differences

  • in fish: skeletal and heart anomalies; linked to nutrition, incubation temp, toxins, and some infections

    • genetic, environmental, infections causes

Aplasia

complete failure of organ to form

Hyperplasia

• increase in # of cells in a tissue or organ

  • organ increases in size by increasing number of cells

  • skin + gills might thicken due to inflammation

Atrophy

• shrinkage in size of cell; loss of cell substance without cell actually dying

  • many cells shrinking so organ does too

  • causes: starvation, low / cut off blood supply, nerve damage, pressure

Hypertrophy

• increase in size of cells and thus organ

  • can be adaptive

    • muscles increase w/ exercise, cardiac hypertrophy due to valve failure

  • can be hormonal response (Gonads) or pathological change (coronary arteriosclerosis in salmon - thickened vessels)

Neoplasia

• new growth; Cancer

  • can be benign

  • local lesions (not spreading)

  • malignant: growing by invasion and spreading to other areas / tissues

Fatty change

accumulation of excess fat within non-fat cells

• tends to happen in liver

• body can't deal with normal amount of fat and also when too much fat

• liver = normal place to store fat → becomes overwhelmed → fats deposited in other locations

Pigments

• melanin can show pathological changes

  • it's normally dark and present in immune cells in fish

  • changes can be response to nerve impulses (colour change, injury)

Calcium

•  hard, white, crunchy

  • might increase in response to cancers, metabolic problems, dietary issues if bad + chronic injuries

Mucus

• substance that can make things translucent/cloudy

  • irritants affecting orgs like skin or gills can cause major changes in quantity and quality of mucus

Latent

hidden (infections)

Chronic

long term, low level (infections)