Koi Herpes Virus (KHV)
Allen C. Riggs DVM, MS
Aquaculture Development Program- Disease
Prevention (ADP-DP)
Hawaii Department of Agriculture
What is KHV?
• Cyprinid herpesvirus-3 or CyHV-3
• DNA virus – family Herpesviridae
• Susceptible species – Common carp
(Cyprinus carpio carpio), Koi (Cyprinus
carpio koi) and Ghost carp (C. carpio goi)
• Resistant species – common goldfish
(Carassius auratus) and grass carp
(Ctenopharyngodon idella)
KHV mortality patterns:
• 80 – 90% mortality in susceptible
populations
• Clinical disease occurs must commonly
when water temperatures are between 22
– 27C (72 – 81F)
• However new cases have been reported in
lower water temperatures down to 18C
(64F)
Signs of KHV:
• Non-specific
• Gill mottling with white necrotic patches
dispersed between normal red gill tissue
• Bleeding gills
• Sunken eyes
• Skin lesions
• Notched nose
Methods of transmission:
• Direct contact with infected fish
• Direct contact with fluids from infected
fish
• Direct contact with water or mud which
infected fish had been exposed to
• Fomites/vectors from contaminated
systems
How do fish become infected?
• Infective virus enters susceptible fish
through gills, skin and possibly gut
• Depending upon water temperature,
susceptible fish that get exposed may
become infected and die
• OR may survive the initial outbreak and
become carriers
Latent carriers
• Survivors of initial infection typically never
show clinical signs again
• However they are still infected and can
spread disease to susceptible fish
• This latent carrier possibility is what
makes KHV especially problematic to
commercial dealers *
Water temperature and KHV:
• Clinical KHV disease has an average incubation
•
•
•
period of 14 days following naïve fish exposed to
infected or carrier fish
Most mortalities occur between 22 and 25.5C
(72 -78F)
Virtually no mortalities above 30C (86F)
New cases have shown clinical outbreaks in
temperatures below 21C (70F)
How to confirm KHV infection:
• No one can tell by just looking at the fish!
• Laboratory tests are required
• Direct methods – actually detect the virus
or “pieces” of its genetic material
• Indirect methods detect antibodies
produced by the fish after exposure to the
virus
Direct methods
• Virus isolation (growing the virus) on
KoiFin (KF) cell lines
• Polymerase chain reaction (PCR)
• Best samples from alive then euthanized
fish – posterior kidney
• Non-lethal samples of blood, feces or gill
clips can be used but results are often less
reliable
Indirect methods:
• Enzyme-linked immunosorbent assay
(ELISA)
• Virus neutralization (VN)
• Non-lethal sample using blood
• A positive ELISA or VN indicates that a fish
has antibodies ( protective immune
product) against KHV virus*
No test answers all KHV questions!
• Negative tests by either direct or indirect
methods do NOT mean fish are not
carriers
• No test definitely detects all carriers or
survivors of outbreaks
• Using diagnostic tests as a part of a
combined preventive strategy is currently
the most practical and cost effective
Why can’t the diagnostic tests give
a definitive answer?
• PCR is the preferred test for confirmation
of active clinical infection – fish are sick
and dying
• PCR can detect some latent carriers but
not all – surveillance screening of “normal”
populations OR fish in quarantine
• PCR is the most economical and easiest to
implement
What about the antibody tests?
• Fish that have antibodies against KHV mean that
•
•
•
they have been exposed to the virus at some
time in the past
Two possibilities – active infection with outbreak
just starting OR latent carrier
Antibody producing immune cells take time to
ramp up with new infections – false negatives
Same cells may slow down or stop antibody
production if non-lethal infection occurred a long
time ago and fish no longer sick – false negative
on carrier state
Individual vs population screening:
• Antibody testing is the preferred method for
•
•
detecting carrier status in valuable individuals *
But what about testing groups of 10, 100 or
1000 fish?
Unless you test them all by antibody detection
methods and get all true negative results each
time – can NOT be 100% sure
How to prevent KHV:
• Quarantine (Q)
• Water temperature in between 21 – 27C
(70 – 80F) …… 24C (75F)*
• 30 day minimum time period
• “Reverse quarantine” after 30 days initial
Q period
• Diagnostic screening tests
Quarantine
• Definition
– Separate tank or pond
w/ separate water &
filtration system
– Preferably located
away from the main
pond
• Time Period
4-6 weeks
Can KHV be treated?
• No treatment for KHV!
• Virus can remain viable for 3 days in water
without fish hosts
• Common disinfection protocols can
eliminate the virus from contaminated
systems and equipment
Regulatory Concerns with KHV:
• 2007 – World Organization for Animal
Health (OIE) added KHV to the notifiable
disease list for finfish
• USDA-APHIS asks accredited veterinarians
and diagnostic labs to report positive
cases to the AVIC of the state in which the
case occurred
Regulatory Concerns with KHV:
• USDA-APHIS has no mandatory
requirements on KHV status for koi
moving interstate or international
• No mandatory depopulation for positive
KHV fish
• KHV now a Hawaii State reportable
disease – positive cases must be reported
to the Hawaii State Veterinarian
Spring Viremia of Carp (SVC)
•
•
•
•
RNA virus
Affects koi & goldfish
Mortality up to 70% in affected populations
Temperature range
12-24°C
54-72°F
• OIE reportable disease
• FAD and mandatory depopulation required by
both State and USDA-APHIS
New USDA Guidelines for SVC
• 8 spp. of fish that are susceptible to SVC are
•
now under USDA oversight for importation into
the U.S.
Required documents
– USDA import permit (form VS-135)
– Veterinary health certificate from the exporting
country
• USDA VS Port Veterinarian must inspect each
shipment at entry port