Shrimp Viruses

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Shrimp Viruses
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Shrimp Viral Diseases

• Baculovirus penaei (BP)
• Infectious hypodermal and hepatopoietic necrosis
  virus (IHHNV)
• Taura Syndrome Virus (TSV)
• White spot syndrome virus (WSSV)

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Baculovirus penaei (BP)

• Occurs over the natural range of all penaeid
  species native to the western hemisphere
• only baculovirus known to have an impact on the
  production of Litopenaeus vannamei
• agent rod-shaped DNA virus, 0.1 µM, cannot be
  seen with light microscope
• pathology infects all life stages of the
  shrimp, except nauplii, horizontally transferred
  in water, passive adherence to eggs and nauplii
  from infected spawners

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Baculovirus penaei (BP)

• External pathology disease expression a
  function of age, culture conditions, amount of
  virus, physiological status
• shrimp must be stressed or compromised by other
  diseases to succumb to BP
• transmission shed in feces of infected shrimp,
  spread orally via ingestion, horizontally,
  passive vertical, incidental in feeds, water,
  sediment

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Baculovirus penaei (BP)

• Diagnosis virus induces formation of
  pyramid-shaped occlusion bodies within nuclei of
  hepatopancreas cells of shrimp
• wet mount of HP tissue
• histopathology
• electron microscopy
• ELIZA
• rapid methodologies??

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Baculovirus penaei

• Control strategies normally applied to shrimp
  hatcheries, where most transmission occurs
• involves stopping transmission of virus from
  broodstock to offspring (REM passive vertical)
• use broodstock SPF for BP (prevention)
• use BP-free water
• drying pond bottom (not really clear connection
  between benthic sediments and BP in grow-out)

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1. WET MOUNT OF FECES, Penaeus vannamei, WITH
TETRAHEDRAL OCCLUSION BODIES 2. GRADE 3 LEVEL OF
INFECTION OF HEPATOPANCREAS
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Infectious Hypodermal and Hematopoietic Necrosis
Virus (IHHN)

• Species affected
• Geographical range western hemisphere
• Description parvo-like virus, 22 nM diam
• Life stages affected L. vannamei much more
  resistant than L. stylirostris, all life stages
  affected, infection during embryo development or
  shortly after hatching results in runt deformity
  syndrome (RDS) in L. stylirostris

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Infectious Hypodermal and Hematopoietic Necrosis
Virus (IHHN)

• Major signs if exposure occurs after PL stage,
  infection limited to cuticle deformities,
  vertical transmission RDS
• transmission rapid infection via ingestion of
  tissues infected with IHHNV, possibly through
  water, embryonic development from parent
• Diagnosis gene probe, RDS size frequency

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IHHNV runt deformity syndrome

• Applies specifically to L. vannamei culture
• harvests contain a large number of small shrimp
  (reduced economic value of crop)
• caused by vertical transmission during ovarian
  development or shortly thereafter
• nursery and grow-out phase affected
• only a problem if PLs came from IHHNV-infected
  broodstock

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IHHNV/RDS

• Diagnosis usually via population size
  distribution characteristics, physical appearance
  of shrimp, IHHNV status
• RDS-affected populations typically have CVs of
  30 or greater within a downward shift in mean
  size
• RDS control use only wild PLs, SPF broodstock

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RDS Size-frequency Distribution
RDS distribution
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RDS Size-frequency Distribution
Normal distribution
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IHHNV
IHHNV-shrimp
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IHHNV-shrimp
HE staining of antennal gland tissue w/Cowdry-A
inclusion body
Feulgen staining of IHHNV infected antennal gland
tissue
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Taura Syndrome Virus

• Primarily affecting Litopenaeus vannamei, L.
  stylirostris appears to be more resistant
• originally reported in Taura River area of
  Ecuador (1992)
• cause agent remained unidentified for many
  years, big political battles over cause in
  Ecuador
• thought to be result of exposure to banana
  fungicides (implicated banana industry)
• up until 1995, scientists in Ecuador were
  claiming a toxic effect (WAS, 1995)
• people were killed over this

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Taura Syndrome Virus (TSV)

• Agent actual agent is a small (30nM)
  icosohedral cytoplasmic virus, possibly in the
  picornavirus group, SS-RNA
• now referred to a Taura syndrome virus
• Life stages principally a disease of juvenile
  P. vannamei, 0l.5-3 g heavy, no sign in nauplius
  - postlarvae
• Infections noted in P. vannamei, P. stylirostris
  and P. setiferus
• Major pathology rapid onset mortality, short
  course, weak, disoriented, soft cuticle, expanded
  chromataphores, tail cuticle necrosis
• survivors are carriers and display cuticle
  degeneration and melanization (cuticle black
  spot), death concurrent w/molting

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TSV Diagnosis

• General rapid mortality of juvenile P.
  vannamei, soft exoskeletons, expanded
  chromataphores, mortality associated with molting
  and severe cuticle black spot lesions
• Histopath buckshot cytoplasmic inclusions
  w/pynotic nuclear debris in necrotic areas of the
  epidermis
• Bioassay subject juvenile SPF indicator shrimp
• PCR polymerase chain reaction on hemolymph,
  amplification of TSV genome in nucleic acid
• Gene probe cDNA probe used in dot blot or
  in-situ hybridization assays

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TSV Control Strategies

• Apart from exclusion, no effective strategies
  have been developed
• very few areas unaffected by this virus
• use of captured wild postlarvae vs. SPF
  hatchery-reared
• manipulation of stocking density (2x)
• use of alternative species (L. stylirostris)
• selective breeding for resistance to TSV

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TAURA SYNDROME VIRUS
1. Moribund, juvenile pond-reaed P. vannamei in
the peracute phase of TSV soft shells,
lethargic, distinct red tail fan 2. Focal
necrosis of tail 3-4. Texas juvenile
pond-reared P. vannamei in the chronic or
recovery phase of TSV (with multiple melanized
foci demonstrating epithelium necrosis)
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White Spot Syndrome Virus (WSSV)

• At least three viruses in the white spot syndrome
  (WSS) complex have been named in the literature,
  all appear very similar
• geographical range reported from China,
  Thailand, Indonesia, Taiwan, Malaysia, even Texas
• first documented case of WSS in western
  hemisphere was recognized in 1995
• found in pond-reared L. setiferus in south Texas

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White Spot Syndrome Virus

• Host range Natural infections have been
  observed in the following species monodon,
  japonicus, orientalis, indicus, merguensis,
  setiferus
• vannamei, stylirostris and all Gulf species
  infected experimentally
• no significant resistance reported for any
  penaeid species

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White Spot Syndrome Virus

• Clinical signs rapid reduction in food
  consumption, lethargy, loose cuticle with white
  spots on inside surface of carapace
• also manifested as red coloration (disease also
  known as red disease, chromatophore
  aggregation, not unique
• 100 mortality within 3-10 days of onset of
  clinical signs
• Presumptive diagnosis clinical signs, history
• Confirmatory diagnosis histological
  demonstration in cuticular, antennal gland,
  lymphoid gland epithelium

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White Spot Syndrome Virus

• Rapid test? squash of gills, appendages or
  moribund shrimp, fixed in methanol, stained with
  Giemsa (bluish inclusion bodies in cells)
• Gene probe (DIG DNA) currently available via
  Diagxotics (dont react to those available for
  other shrimp viruses)

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WHITE SPOT VIRUS (Penaeus monodon)
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Aquaculture Virus Management

• Currently proposed Office International des
  Epizooties (OIE) certification
• French organization gaining popularity
• looks at animals, frozen fresh products, feed,
  surveillance, trafficking, diagnoses
• represents only international effort since 1924
  (World Organization of Animal Health)
• 9 out of 10 problems are with crustacean diseases

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Aquaculture Virus Management

• Problem we lack OIE-type diagnostics for shrimp
• tissue cultures are difficult
• histopathology lacks sensitivity
• molecular rapid, but developed quickly and
  lacks validation
• viruses big bucks hence
• TSV, WSSV, YHV classified as notifiable
• non-notifiable BVMGN, BP, MBV, IHHN (can work
  around these)

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Shrimp Virus Agents
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Shrimp Virus Diagnosis
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Shrimp Virus Diagnosis