KOI Herpes Virus (CyHV-3)
Eighty representatives from all phases
of pond care met recently at the University of Georgia's Koi Lab
for a Koi Health Management Course. We had veterinarians,
hobbyists, dealers, fish farmers, and pond construction
companies assembling to learn more about fish health. One
of the hottest topics was Koi Herpes Virus. I thought you
might like the latest information.
A few facts as known today:
-
KHV survivors- all post-infected fish
are carriers. They can never leave the pond and you can
never safely add new fish. We do not know how long the fish
will remain immune. Virus can't replicate on its own and
dies in 4 hours, but can easily be disinfected by weak
bleach solution.
-
Frogs can transfer KHV from one pond to
another via the slime on their backs but are not themselves
carriers. KHV is species-specific.
-
74ºF activates the disease. Indonesia
is now a test zone for KHV vaccination (Magnoy products) due
to their heavy outbreaks. At 30ºC fish are "heat
synchronized" (per Doc Johnson) which is what Magnoy is
calling "Immunized." There is no such thing as immunity
until we have a vaccination that is proven successful.
-
Once the virus is "shed" from
vaccinated koi into the environment, the EPA becomes
involved to do non-target testing to rule-out impact on
other species.
-
Stress does not bring on the virus.
Temperature does. Therefore, fish kept in a spring-fed pond
with temperatures in the 60's can be KHV+ and never have the
disease break until the fish leave the pond and go to a new
home.
Vicki Vaughan says it takes a HUGE viral
load to transmit the disease. We've never seen a case where it
was spread without active shedding. Splashing water or sharing
nets is doubtful as they have a difficult time infecting fish at
the lab for testing. She says, yes, exercise caution at shows,
but probably the disease is not going to be transferred. In the
end, why take the chance?
Dr. Helen Roberts, DVM recommends
sending samples (biopsy) of gill, spleen, liver and kidney of
any suspected fish to the lab for analysis. As with any other
disease, the quicker you act, the better the prognosis for the
fish (the rest of the fish).
She also mentioned developing a "pathic
pheumonic" in which anytime you see a symptom which resembles
KHV (for example), really see it. (I hope I described
that right.) It doesn't pay to put on the horse blinders today.
KHV isn't limited to imported koi. Domestic koi are just as
likely to be exposed, infected or diseased.
Dr. Branson Ritchie asked us to consider
certain aspects of working with a latent virus such as herpes
which is contagious when it "sheds"-
A few notes on
ISOLATION/QUARANTINE:
-
This
means no direct or indirect contact with other fish.
-
Sterilization of air, food, water, etcetera.
-
No
visitors.
-
Not
practical for companion animals.
-
Animal
does not leave for any reason during quarantine period.
For fish dealers to do the quarantine
and isolation, there are disadvantages.
-
One is that the fish are generally sold
quickly, not allowing a 14-30 day quarantine period.
-
They must test every fish that comes
into their possession/store.
-
A negative population is highly suspect
(parasites, at the very least, should be identified and
eradicated before resale).
-
Tests are not absolute for KHV (there
is a 2-3 week window period after infection before
antibodies can be detected in the fish's blood)
-
What do you do with positive fish?
-
Do you also euthanize companion fish?
-
Would a test and eradication program be
effective with a virus that causes a latent infection? (
i.e. - chicken pox is a herpes virus and remains in your
body until you die. Does this make you a chicken pox
carrier? It hasn't been proven that you aren't.)
-
Virus incubation period is 5-14 days at
74ºF.
-
Any koi is susceptible to infection
. Very small koi are susceptible to disease.
Progression of disease: a) exposure…b) infection… c)
disease.
-
IF this really is a herpes virus (KHV),
then quarantine is of little value. As yet we have no
treatment for KHV. Statistics at UGA's koi lab in the past
year were 15 out of 162 tested positive for KHV.
This means one tenth of the koi
population is latently infected and we do not know how long the
antibody titers last. To put one infected koi into your pond
can spell disaster for the entire population. What quarantine
will do, if done for 14 days at 74ºF, will remove any doubt that
incoming fish are actively diseased, but won't tell if the fish
is a carrier.
Since the antibodies can be detected 2-3
weeks after the fish has been infected, maybe the only way to be
sure a newly purchased fish is safe to take out of quarantine
and introduce into a pond is to have the antibody test done
after 2-3 weeks in quarantine. The quarantine could be either
in a dealer's or hobbyist facility. The likelihood of buying an
infected or previously infected (carrier) fish is greater than
you think.
-- by Carolyn Weise
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