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FISH 424: Fish Health Management
Virology Lecture:
ISAV
SVCV
WSIV
VHSV
Infectious Salmon Anemia
Virus (ISAV)
• Hosts and Geographic Range
– Highly infectious for Atlantic
salmon
– potential asymptomatic carriers
of the virus
• Searun brown trout
• rainbow trout
• Atlantic herring
Infectious Salmon Anemia
(ISAV)
• Viral infection is found in
Seawater (Net pens):
–
–
–
–
Norway (1984)
United Kingdom (1998)
East coast Canada (1998)
East coast United States
(2000)
– Chile (1999)
CANADA
MAINE
Infectious Salmon Anemia (ISAV)
• Etiological agent
– 1st described as
Hemorrhagic Kidney
Syndrome
– member of the
orthomyxoviridae
family.
– 8 negative strands of
RNA enclosed in a lipid
envelop
– Virions between 45-140
nm in diameter
Infectious Salmon Anemia (ISAV)
Transmission Electron Micrographs
Infectious Salmon Anemia (ISAV)
• Virulence and Pathology
– lethargic, swim near the water
surface
– petechial hemorrhage on skin
and fins
– anemia, exophthalmia, ascites
– Pale gills
– hepatomegally, splenomegally
– petechia in the visceral fat
Infectious Salmon Anemia (ISAV)
Infectious Salmon Anemia (ISAV)
• Transmission:
– Almost exclusively occurrs
during saltwater stages
– Horizontal (fish to fish contact)
– Coprophagy (feeding on feces)
– Sea lice can transmit ISAv from
infected to susceptible fish
– Transfer by contaminated
equipment / People / boat traffic
/ location near fish processing
plants
Infectious Salmon Anemia (ISAV)
Figure 3. Infection status of areas versus number of well-boat visits. Infection
status is 0 for no infection, 1 for suspected infection, and 2 for confirmed
infection
Alexander G. Murray,*† Ronald J. Smith,* and Ronald M. Stagg*
*Fisheries Research Services Marine Laboratory, Aberdeen, United Kingdom; and †University of Aberdeen, Aberdeen,
United Kingdom
Infectious Salmon Anemia (ISAV)
• Diagnosis
– Isolation through tissue culture
• SHK-1 and CHSE-214
cells
– IFAT (indirect fluorescent
antibody test) on tissue
imprints
– RT-PCR (reverse transcriptase
poylmerase chain reaction)
Infectious Salmon Anemia (ISAV)
•
Management
–
Since the virus is readily transmitted in seawater
–
Shown net pen operations within 5-6 km of an infected site can
become contaminated
1.
culture sites be spaced no less than 5-6 km apart
2.
waste water from slaughter and processing facilities should be
thoroughly disinfected
3.
control of ship and personnel movements among sites
4.
compulsory slaughter of infect stocks (eradication)
5.
Attempts to require vaccination
Spring Viremia of Carp Virus (SVCV)
• Hosts and Geographic Range
– Natural infections have been
recognized in common carp and
koi carp (Cyprinus carpio)
– Historically only in Europe and
Russia
– Recently, SVC has been
reported in koi in the United
States for the first time
Recent News Headlines
1. Spring Viremia of Carp virus (SVCv) was recently identified
in a backyard koi and goldfish pond located in Snohomish
County, Washington State
2. Spring viremia of carp (SVC) was confirmed in
ornamental koi carp in Pike County, Missouri on
July 13, 2004
3. SVC has previously been reported in Europe, the Middle
East and Asia. More recently, it has been reported in North
and South America. In the US, SVC outbreaks occurred in
North Carolina in 2002 and Washington in June 2004. The
virus has also been reported in feral common carp
populations in Wisconsin and Illinois. SCV is an OIE
notifiable disease.
Spring Viremia of Carp Virus
• Etiological agent
– Family
Rhabdoviridae
– Bullet shaped
morphology
– single-stranded
RNA containing 5
genes
Spring Viremia of Carp Virus
• Virulence and Pathology
–
–
–
–
Darkening of the skin
Distended abdomen
Exopthalmia
Petechial hemorrhage of
the skin, gills, and eyes
– Pale gills
– Hemorrhage in the swim
bladder
– Catarrhal enteritis
Example of exopthalmia and abdominal distention
Clinical signs of disease:
•Darkening coloration
•Abdominal distension
•Exopthalmia
Spring Viremia of Carp Virus
• Virulence and Pathology
– virus affects carp at all ages but victims are
mostly young fish.
– Outbreaks depend on the temperature
– High mortality occurs at water temperatures of
10 to 17°C, typically in spring.
– At >20 °C, elevated immune response protects
carp from infection and re-infection
Spring Viremia of Carp Virus
• Transmission:
– Occurs by horizontal transmission
– Excretion of SVCV via feces and urine from
infected fish
– Parasitic transfer of SVCV from diseased
to healthy fish
– virus could stay infective in the water for
more than 4 wks and 6 wks in the mud
– source of infection may be contaminated
equipment
– vertical transmission of SVCV is not an
important source of infection
Spring Viremia of Carp Virus
• Diagnosis (Standard Screening Method )
– Isolation of SVCV in cell culture
• FHM or EPC tissue culture cells
– Indirect fluorescent antibody test on infected
culture cells
or
– Enzyme-linked immunosorbent assay (ELISA)
or
– Neutralization Antibody test
or
– PCR
Spring Viremia of Carp Virus
• Management
– In rearing facilities with a controlled environment, elevation of
temperature above 20° C can prevent or stop SVC outbreaks
– avoidance of SVCV by using spring or well water
– Eradication of diseased fish
– Control movement of fish
• Anglers should not transfer fish or fish parts from one body of water to
another
– Vaccination provides good protection
White sturgeon iridovirus (WSIV)
• Host and Geographic
Range
– White Sturgeon
– North America
WSIV History
• Recognized as the most prevalent
viral pathogen in White Sturgeon.
• Significant mortality in commercial
and conservation aquaculture.
• Northern
California commercial sturgeon
farms
• Lower Columbia River in Oregon and
Washington
• Snake River in Southern Idaho
• Kootenai River in northern Idaho
• British Columbia
LaPatra et. al. 1994
WSIV: Manifestation of Disease
• Clinical disease can be induced
– Overcrowding, transport,
handling, etc.
• Slow chronic wasting syndrome
• Fry and fingerlings (1st year)
• Mortality assumed to be due:
– Anorexia
– Respiratory function
– Osmoregulatory function
– Secondary infection
WSIV: Clinical Signs of Disease
Darkening Pigmentation
Emaciated body
Manifestation of disease
Virus has an affinity for
epithelial tissue:
• Skin
• Gill
• Oropharynx
• Olfactory (barbels)
Histology shows:
•Hypertrophied cells with swollen cytoplasm
TEM of WSIV infected cells
5000X
WSIV Morphology
• Icosahedral morphology
• Size (250-300nm)
• Double capsid
• Dense nucleiod center
TEM of WSIV From Kootenai River white sturgeon skin
(2004)
White sturgeon iridovirus (WSIV)
• Transmission
– Shown to be transmitted from infected fish to
healthy individuals
– may be endemic in most wild Northwest white
sturgeon populations.
– Virus may be vertically transmitted from adult
to offspring during spawning.
White sturgeon iridovirus (WSIV)
• Diagnosis of infection
– Difficult to propagate
reliably in tissue culture
– Histology for the
detection of large
hypertrophied cells
within the epithelial
tissue of the skin, gills,
and barbels.
White sturgeon iridovirus (WSIV)
• Management
– Ideally, avoidance of WSIV by using spring or
well water to rear juvenile sturgeon
– Minimize stress of sturgeon during early life
stage
– Control movement of fish
Viral Hemorrhagic Septicemia is 1 of the 7 most
important diseases of finfish worldwide and is
listed by the OIE as notifiable
O.I.E. World Organization for Animal
Health
Aquatic Animal Health Code 2006
USDA Animal and Plant Health Service
Designated at the US Regulatory Authority on
Animal Health
USDA APHIS Criteria for Diseases/Pathogens
of Regulatory Significance
• Causes significant impact on production, wild
resources, or human health
• Infectious disease and can be spread by
commerce
• Involves host species in interstate or
international commerce and be of concern to
US trading partners that are free of the disease
• Reliable diagnostic methods available
USDA APHIS Criteria for Diseases/Pathogens
of Regulatory Significance
• Causes significant impact on production, wild resources, or human health
• Infectious disease and can be spread by commerce
• Involves host species in interstate or international commerce and be of
concern to US trading partners that are free of the disease
• Reliable diagnostic methods available
• No human health risk with VHSV
• No treatment for VHSV
• VHSV has been found ONLY in wild fish in
the Great Lakes Basin
Time Line of VHSV
•
•
•
•
1938- described in RBT in Europe (FW)
1963- virus isolated and described (FW)
1988- saltwater (SW) VHSV hosts in USA
1990 to present- VHSV is found endemic in
SW hosts on US East and West Coasts
• 2003-present- Great Lakes VHSV causes mass
mortality in a variety of FW hosts, including
sport fish important to Idaho
How bad can it get?
•
•
•
•
2006 Freshwater drum mortality in Lake Erie
New virus in naïve hosts becomes epizootic
Millions of pounds of FW drum
“Windrows of fish” along the beach piled up
10’ wide and 4’ high
Herring mortality B.C. Canada
Herring
Rainbow trout
Walleye
Disease Signs of VHSV
Hemorrhagic: Causes leaking of blood from vessels
especially under the skin and internal organs
Septicemia: Virus in blood and spreads
throughout the body in circulation
Pop eye: Caused by pressure of hemorrhage
pushing beneath the eye
Host Range of VHSV
• 37 host species FW and SW worldwide
• 28 FW species
• 19 FW species are important to Idaho
including rainbow trout, salmon, bass,
bluegill, crappie, and perch
• Host range is unheard of for other fish
viruses!
Current VHS Outbreaks:2007
St. Lawrence R.
Lake Huron
Lake
Winnebago*
Budd
Lake*
Lake Ontario
Lake
Michigan
Lake St. Clair
Conesus Lake*
Lake Erie
* Not connected by water – baitfish suspec
Current VHS Outbreaks:2007
St. Lawrence R.
Lake Huron
Lake
Winnebago*
Budd
Lake*
Lake Ontario
Lake
Michigan
Lake St. Clair
Conesus Lake*
Lake Erie
Summer, 2007 NYDEC
Surveillance
Genetic Differences of VHSV
Shows an East Coast Origin
3.7%-5%
2.1%
How did VHSV get into the Great
Lakes?
Commercial ballast water
Natural movement of infected fish
Human recreational activities
• Sport fishing activities (bait minnows, contaminated
fishing equipment, illegal fish stocking)
• Boating
Animal activities (mammals, birds)
Basically, vectors are unknown!
Overview
Two genetic types of VHSV correlate West coast
and East Coast
VHSV in the Great Lakes likely came from an East
Coast host
Conventional cell culture methods detects Great
Lakes VHSV strains
VHSV is more stable in freshwater than in sea
water.
VHSV lasts up to one month when held at 50ºF
APHIS Federal Order
• VHSV Federal Order was issued
10/24/2006
• Emergency Action taken to prevent the
spread of VHSV
• Must be followed-up by formal
rulemaking
Current Provisions Under the
Federal Order
• VHS susceptible species are prohibited from moving
out of the 8 States and 2 Canadian Provinces
bordering the Great Lakes except under certain
conditions
– Movement to slaughter with adequate disinfection
– Movement to a research or diagnostic lab with adequate
disinfection
– Movement of live fish testing negative for VHSV by
laboratory assays
– Movement of salmonids from Canada that meet
USFWS inspection requirements
• Catch-and-Release fishing activities
Implications of VHSV for Idaho
• 20 years surveillance has been negative
in cultured and wild fish
• Sport fishing valued at $ 360 million
• $ 110 million trout culture industry at risk
• ESA-listed anadromous salmon and
steelhead cultured in Idaho
• Must prevent VHSV introduction into Idaho
What has IDFG done to reduce risk?
• Live fish for bait prohibited
• Banned importation of all fish from Great
Lakes Basin (GLB)
• Supported APHIS Federal Order
• Banned frozen baitfish from GLB
• Partnering with Idaho Department of
Agriculture and trout industry on
emergency rule to prevent introduction
Future needs:
• Risk assessment of potential vectors leading to
Biosecurity Plan for Idaho
 Importations of live fish & eggs
 Private ponds
 Aquatic nuisance species
 Aquatic baits other than fish
• Education of anglers to reduce risks
• Support research on VHSV susceptibility of Idaho
fish stocks
• Idaho Fish Health and Sterility Management
Policy