Download Lecture 3: Aquaculture Viruses

Aquaculture Viruses
Major Viral Infections in Fish
• Infectious pancreatic necrosis (IPN)
• Viral hemorrhagic septicemia (VHS)
• Infectious hematopoetic necrosis (IHN)
• Channel catfish virus disease (CCVD)
(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 1960’s, wiped out brook
trout in Oregon in 1971-73
• Size: Only 65 nM in diam., smallest of fish viruses
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
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
IPN: pathology (what do we see?)
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!
How Bad Can It Be??
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)
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)
More…
•
halibut (Hippoglossus stenolepis)
Jap. amberjack (Seriola quinqueradiata)
lampreys (Petromyzontyidae)
loach (Misgurnus anguillicaudatus)
masou salmon (Oncorhynchus masou)
perches (Percidae)
silversides (Atherinidae)
soles (Soleidae)
striped snakehead (Channa striatus)
summer flounder (Paralichthys dentatus)
white seabass (Moronidae)
carp (Cyprinus carpio)
redfin perch (Perca fluviatilis)
yellowfin bream (Acanthopagrus australis)
herrings/sardines (Clupidae)
lake trout (Salvelinus namaycush)
left-eye flounders (Bothidae)
loaches (Cobitidae)
Pacific salmon (Oncorhynchus spp)
pikes (Esocidae)
sockeye salmon (Oncorhynchus nerka)
Southwest European nase (C. toxostoma)
suckers (Cotostomidae)
turbot (Psetta maxima)
whitefish (Coregonidae)
goldfish (Carassius auratus)
southern flounder (P. lethostigma)
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)
Infectious pancreatic necrosis in Atlantic salmon.
pike (Esox lucius)
Note swollen stomach and 'pop eye'
river lamprey (Lampetra fluviatalis) Source: Australian Animal Health Laboratory
shore crab (Carcinus maenas)
Spanish barbel (Barbus graellsi)
white suckers (Catostomas commersoni)
...what now???
(2) Viral Hemorrhagic Septicemia (VHS)
(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
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
Viral Hemorrhagic Septicemia (VHS)
• Pathogenesis: infection results in viremia, disrupts many
organ systems, 200-300g fish most affected
• Environmental factors: low temp (< 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
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.
Viral Hemorrhagic Septicemia (VHS)
External hemorrhages
Liver red in acute stage
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”
Type
Prevalent host type and location
I-a
Farmed rainbow trout and a few other freshwater fish in continental
Europe[10]
I-b
Marine fish of the Baltic Sea, Skagerrak, Kattegat, North Sea,
Japan[1]
I-c
Farmed rainbow trout Denmark
I-d
Farmed rainbow trout in Norway, Finland, Gulf of Bothnia
I-e
Rainbow trout in Georgia, farmed and wild turbot in the Black Sea[11]
II
Marine fish of the Baltic Sea
III
Marine fish of the British Isles and northern France, farmed turbot in
the UK and Ireland, and Greenland halibut (Reinhardtius
hippoglossoides) in Greenland[12]
IV-a
Marine fish of the Northwest Pacific (North America), North
American north Atlantic coast,[13] Japan, and Korea[1][14]
IV-b
Freshwater fish in North American Great Lakes region[14]
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.
(3 ) Infectious Hematopoietic Necrosis
(IHN)
• Who: sockeye, chinook, rainbows; cohos resistant
• When?: 1950’s 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
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
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
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.
(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.
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
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.
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...
Channel Catfish Virus Disease
Channel Catfish Virus Disease
However, you can always take precautions!