Aquaculture Viruses

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Aquaculture Viruses
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What a Virus Isnt

• Not a bacterium...
• Not independent...
• Cannot survive in absence of a living cell within
  which to replicate...
• Antibiotics generally dont work on them...

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What Viruses Are...

• Infectious agents composed mainly of nucleic acid
  with a protein coat (capsid)
• Visible with electron microscope (10-200 nM)
• Carry on normal cell-like function (unless free,
  then infectious)
• In infectious form no growth no respiration???
• Can enter living plant, animal or bacterial cell

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Virus Appearence?

• Capsid, core and genetic material (DNA/RNA)
• Capsid outer shell of the virus which encloses
  genetic material (link chemical structure of
  capsid helps determine immune response to virus)
• capsid is made of many identical individual
  proteins
• protein core under capsid protecting genetic
  material
• sometimes an additional covering (lipid bilayer
  w/embedded proteins) on outside known as an
  envelope ( like a baseball)
• various forms rods, filaments, spheres, cubes,
  crystals

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Capsid
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capsomere unit/molecule associated with capsid
structure
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Typical Virus Shapes
SPHERES
RODS
CUBES
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More Virus Shapes
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Composition of T-Even Bacteriophage

• Capsid brains of virus, tightly-wound protein
  protecting nucleic acids
• Body attached to capsid head, rod-like
  structure w/retractible sheath, hollow core
• Tail at end of core is a spiked plate carrying
  6 slender tail fibers, anchor virus to its host

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How do viruses work?

• Viruses make use of the host cells chemical
  energy, protein and nucleic acid synthesizing
  ability to replicate themselves...
• each virus attacks a specific type of cell
• cold viruses attack cells of the lung
• the AIDS virus attacks T4 cells of the
• immune system
• fish viruses are just as specific

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Bacteriophage Attack
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Virusal Mechanism

• Viruses contain single- or double- stranded DNA
  or RNA
• Often, the virus alters the intracellular
  environment enough to damage or kill the cell
  (oops!!)
• If enough cells are destroyed, disease results!

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Role of RNA/DNA

• Supplies the codes for building the protein coat
  (capsid) and for producing enzymes needed to
  replicate more viruses
• Information given so newly-built viruses can lyse
  cells (e.g., bacteriophage)
• Result cell destroyed.

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Bottom Line...

• All viruses only exist to make more viruses
• Most are harmful
• Replication host cell death.

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The Virus Invasion Step by step

• Phase 1 Attachment of virus to bacteria, etc.
• Phase 2 injection of DNA or RNA
• Phase 3 DNA (RNA) enters the host cell
• Phase 4DNA incorporated (10 minutes) hundreds of
  virions appear causing the cell to rupture,
  releasing hundreds of small viral replicates
• This is how it can replicate so quickly!

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The Virus Invasion
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Whats Infected by a Virus?

• All living things have some susceptibility to a
  particular virus
• Virus is specific for the organism
• Within a species, there may be a 100 or more
  different viruses which can affect that species
  alone
• Specific for example, a virus that only affects
  one organism (humans and smallpox)
• Influenza can infect humans and two animals

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Different Types of Viruses

• Major classifications animal, plant, bacterial
• Sub-classified by arrangement and type of nucleic
  acid
• Animal virus group double-stranded DNA,
  single-stranded DNA, double-stranded RNA,
  single-stranded RNA, retrovirus
• Influenza SS-RNA

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Do Viruses ever Change?

• Mutations do occur.
• If the mutation is harmful, the new virus
  particle might no longer be functional
  (infectious)
• However, because a given virus can generate many,
  many copies, a small number of non-functional
  viruses is not important
• Mutation is not necessarily damaging to the virus
  -- it can lead to a functional but new strain of
  virus

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Defense Against Viruses

• First Line skin and mucous membrane, which also
  lines the gastrointestinal and respiratory
  passageways
• skin is tough and stomach acidity acts as a
  disinfectant
• Second Line after the virus enters the blood
  and other tissues, white blood cells and related
  cells (phagocytes) consume them
• accumulation of phagocytes in area of infection
  is known as puss

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Defense Against Viruses
Antibodies attacking chickenpox virus
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Defense Against Viruses

• Antibodies are the best defense against viruses
• unfortunately, they are specific in their action
• chickenpox antibody will only attack a chickenpox
  virus
• a particular virus stimulates the production of a
  particular antibody

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Defense Against Viral Infection

• Animals are protected in several ways
• 1) intracellular if a particular virus attacks
  cells, our bodies produce interferons
• interferons (alpha, beta or gamma) are proteins
  which interact with adjacent cells and cause them
  to become more resistant to infection by the
  virus
• if the resistance is not quite good enough, we
  become sick

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Defense Against Viral Infection

• 2) immune system (extracellular) kills the
  virus outside the cell
• also kills the infected cells
• virus cannot spread
• eventually the virus is completely removed and we
  get better
• exception HIV because it infects cells of the
  immune system, itself
• chemicals/drugs acyclovir, AZT, HIV protease
  inhibitor, several fish vaccines available.

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Major Fish Viruses
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Major Viral Infections in Fish

• Infectious pancreatic necrosis (IPN)
• Viral hemorrhagic septicemia (VHS)
• Infectious hematopoetic necrosis (IHN)
• Channel catfish virus disease (CCVD)

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(1) Infectious Pancreatic Necrosis (IPN)

• What? viral infection of salmonids (trout and
  char)
• Time Acute
• Result high mortality (fry and fingerlings)
• Rare in larger fish (good thing!)
• History Isolated in Pacific NW in 1960s, wiped
  out brook trout in Oregon in 1971-73
• Size Only 65 nM in diam., smallest of fish
  viruses

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IPN general notes

• Single capsid shell, icosohedral symmetry, no
  envelope
• Contains two segments of DS-RNA
• Fairly stable and resistant to chemicals (acid,
  ether, etc.), variable resistance to freezing
• Remains infectious for 3 months in water (uh oh!)
• Targets pancreas and hematopoietic tissues of
  kidney and spleen

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IPN epizootiology (disease process)

• Who? All salmonids, brook trout most
  susceptible, marine fish (flounder?)
• Reservoirs (where)? carriers, once a carrier
  always a carrier, virus particles shed in
  feces/urine
• Transmission (how?) horizontal, by waters via
  carriers or infected fry vertical from adults to
  progeny experimentally by feeding infected
  material, IP injection
• Pathogenesis entry via gills, digestive tract
• Environmental factors mortality reduced at
  lower temps (why?) however, carriers not reduced

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IPN pathology (what do we see?)
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IPN detection, diagnosis and control

• Isolation whole fry, kidney, spleen, pyloric
  cecae, sex fluids are all good sources, .i.e.
  check these!!!
• Presumptive tests epizootiological evidence
  and/or typical PCR in infected cells
• Definitive tests serology (fluorescent antibody
  test (FAT))
• Control avoid virus in water, virus-free stock,
  destruction of infected stock, vaccine exists
  now!

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How Bad Can It Be??
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Fish severely affected by IPNV

• Atlantic salmon (Salmo salar)brook trout
  (Salvelinus fontinalis)brown trout (Salmo
  trutta)danio zebrafish (Brachydanio
  rerio)rainbow trout (Oncorhynchus
  mykiss)yellowtail (Seriola lalandi)

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Other species known to be susceptible

• amago salmon (Oncorhynchus rhodurus)Arctic char
  (Salvelinus alpinus)Atlantic menhadden
  (Brevoortia tyrannus)carangids
  (Carangidae)chinook salmon (Oncorhynchus
  tshawytscha)chum salmon (Oncorhynchus
  keta)cichlids (Cichlidae)coho salmon
  (Oncorhynchus kisutch)common scallop (Pecten
  maximus)cutthroat trout (Salmo clarki)cyprinids
  (Cyprinidae)Danube salmon (Salmo
  hucho)drums/croakers (Sciaenidae)eels (Anguilla
  spp)grayling (Thymallus thymallus)

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More

• halibut (Hippoglossus stenolepis) herrings/sardin
  es (Clupidae)Jap. amberjack (Seriola
  quinqueradiata) lake trout (Salvelinus
  namaycush)lampreys (Petromyzontyidae) left-eye
  flounders (Bothidae)loach (Misgurnus
  anguillicaudatus) loaches (Cobitidae)masou
  salmon (Oncorhynchus masou) Pacific salmon
  (Oncorhynchus spp)perches (Percidae) pikes
  (Esocidae)silversides (Atherinidae) sockeye
  salmon (Oncorhynchus nerka)soles
  (Soleidae) Southwest European nase (C.
  toxostoma)
• striped snakehead (Channa striatus) suckers
  (Cotostomidae)
• summer flounder (Paralichthys dentatus) turbot
  (Psetta maxima)white seabass (Moronidae) whitef
  ish (Coregonidae)carp (Cyprinus
  carpio) goldfish (Carassius auratus)redfin
  perch (Perca fluviatilis) southern flounder (P.
  lethostigma)yellowfin bream (Acanthopagrus
  australis)

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Asymptomatic carriers...

• coalfish (Pollachius virens)common carp
  (Cyprinus carpio)discus fish (Symphysodon
  discus)goldfish (Carrasius auratus)heron (Ardea
  cinerea)loach (Cobitidae)minnow (Phoxinus
  phoxinus)noble crayfish (Astacus astacus)pike
  (Esox lucius)river lamprey (Lampetra
  fluviatalis)shore crab (Carcinus maenas)Spanish
  barbel (Barbus graellsi)white suckers
  (Catostomas commersoni)

Infectious pancreatic necrosis in Atlantic
salmon. Note swollen stomach and 'pop eye'
Source Australian Animal Health Laboratory
...what now???
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(2) Viral Hemorrhagic Septicemia (VHS)
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(2) Viral Hemorrhagic Septicemia (VHS)

• What? Viral disease of European salmonids
• When? Recognized in Denmark in 1949, isolated
• from Pacific Coast in 1989
• Size rhabdovirus, bullet-shaped (one rounded
  end), 185 x 65 nM, lipoprotein envelope
• non-segmented SS-RNA
• Constitution sensitive to ether and chloroform,
  heat, acid, resistant to freeze-drying

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Viral Hemorrhagic Septicemia

• Produces a general viremia, tissue and organ
  damage, liver necrosis, spleen, kidney
• Epizootiology cultured rainbow trout, also
  brown trout, steelhead, chinook, coho (most
  cases in WA state)
• Reservoirs again...survivors are life-long
  carriers, usually rainbow trout, brown in Europe
• Transmission horizontal through water, virus
  can occur on eggs spawned by carriers, IP
  injection, birds, hatchery equip

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Viral Hemorrhagic Septicemia (VHS)

• Pathogenesis infection results in viremia,
  disrupts many organ systems, 200-300g fish most
  affected
• Environmental factors low temp (lt 8oC, 46oF)
• External pathology lethargy, hanging downward
  in water (dropsy), swimming in circles,
  exopthalmia, dark discoloration, hemorrhages in
  roof of mouth, pale gills w/focal hemorrhages

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Viral Hemorrhagic Septicemia (VHS)

• Internal pathology gut devoid of food, liver
  pale, hemorrhages in connective tissue, kidney
  gray and swollen (chronic), red and thin (acute)
• Histopathology necrosis of liver, kidney
  nephrons, spleen, pancreas, melanin in kidneys
  and spleen (OUCH!)
• Isolation/tests isolated from kidney/spleen,
  epizootiological evidence, definitive test is
  serum neutralization, or FAT.

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Viral Hemorrhagic Septicemia (VHS)
External hemorrhages
Liver red in acute stage
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Viral haemorrhagic septicaemia in rainbow trout.
Note pale color of stomach region, pinpoint
haemorrhages in fatty tissue, and pale gills
Source T Håstein
Viral haemorrhagic septicaemia in rainbow trout.
Note swollen stomach and pop eye
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Viral Hemorrhagic Septicemia

• Prevention clean broodstock, water fish,
  avoid infected broodstock, test and slaughter
• Can spread very quickly from farm to farm avoid
  close proximity to other farms
• Vaccines are under development.
• One EPA-approved disinfectant Virkon AQUATIC
  (made by Dupont). Bleach kills the VHS virus.

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(3 ) Infectious Hematopoietic Necrosis (IHN)

• Who sockeye, chinook, rainbows cohos resistant
• When? 1950s in Oregon hatcheries. 100 million
  mortalities between 1970-1980, if infected, 70
  mortality likely, esp. in young fish (fry 90-95
  mort. possible)
• What? bullet shaped rhabdovirus, non- segmented
  SS-RNA, sensitive to heat and pH, glycoprotein is
  spiked on surface of virus

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Infectious Hematopoietic Necrosis (IHN)

• Reservoirs survivors life-long carriers, adults
  shed virus at spawning
• Transmission horizontal, primary mode is
  vertical via ovarian fluid (virus hitches ride on
  sperm into egg) however, feces, urine, and
  external mucus possible. Also, feeding and
  inoculation have worked experimentally
• Pathogenesis gills suspected incubation period
  depends on temp, route, dose, age extensive
  hemorrhaging, necrosis of many tissues death
  usually due to kidney failure

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Infectious Hematopoietic Necrosis (IHN)

• Environmental factors temp. very important,
  slows below 10?C, holding in tanks/handling
  increase severity
• External pathology lethargy, whirling, dropsy,
  exopthalmia, anemia, hemorrhaging of
  musculature/fins, scoliosis
• Internal pathology liver, kidney, spleen pale
  stomach/intestines filled with milky fluid
  petechial hemorrhaging
• Histopathology extensive necrosis of
  hematopoetic tissue of kidney/spleen

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Infectious Hematopoietic Necrosis (IHN)

• Definitive diagnosis serum neutralization, FAT,
  ELISA
• Prevention avoidance, quarantine, clean water
  with UV, ozone, virus-free stock test,
  slaughter, disinfect disinfect eggs vaccines
  under development elevated water temp
• No vaccines as of June 2007.

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(4) Channel Catfish Virus Disease (CCVD)

• Contagious herpes virus affecting only channel
  catfish less than four months old
• Occurs in SE United States, California, Honduras
• Acute hemorrhagia, high mortality, first
  discovered in 1968
• Agent enveloped capsid, icosohedral
  nucleocapsid with 162 capsomeres
• Physio/chemical properties easy to kill,
  sensitive to freeze-thaw, acid, ether, etc.

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Channel Catfish Virus Disease (CCVD)

• Environmental factors optimal temperature
  28-30?C, common during warmer months, cooler
  water big difference
• epizootiology horizontal, vertical suspected
• external pathology spiral swimming float with
  head at surface hemorrhagic fins, abdomen
  ascites pale or hemorrhagic gills exophthalmia

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Channel Catfish Virus Disease (CCVD)

• Internal pathology hemorrhages of liver,
  kidney, spleen, gut, musculature congestion of
  mesenteries and adipose
• Histopathology necrosis of kidney, other
  organs macrophages in sinusoids of liver, etc.
  degeneration of brain
• Presumptive diagnosis clinical signs,
  epizootiological evidence
• Definitive diagnosis SN or FAT.

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Channel Catfish Virus Disease (CCVD)

• Prevention avoid potential carriers (survivors)
  or infected fry, keep temperature below 27oC
  (will still produce carriers), attenuated vaccine
  shows some promise
• Therapy none available...

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Channel Catfish Virus Disease
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Channel Catfish Virus Disease
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However, you can always take precautions!