The information below is
reprinted from Koivet.com
with the owner's permission.
Koi are generally hardy fish.
They're descended from the common carp and are
tough, essentially omnivorous fish with the ability
to withstand a range of living conditions.
ornamental specimen, the Koi is beautiful, and
sought after for it's highly strained color
Koi health and
disease is essentially a balancing act or
"equilibrium" created between stocking density,
water-and-environmental conditions, parasites, and
the fish itself.
It was once said
that "if you take care of the environment, the fish
will take care of themselves". This was true until
some of these viruses started showing up with
There are two known viruses of
importance to Koi. There are other viruses but these
are important from the perspective that they can
quickly kill the fish and are both highly
These viruses are
similar and dissimilar. Some of their differences
and similarities are important.
No. This virus was
described in the literature more than forty
No. KHV was reported in
Japan fully ten years before it's first
outbreak or discovery in Israel. The
earliest documentation I can find is from
SVC has recently been
shown to kill groups of fish when
experimentally injected with the virus,
earlier researchers maintained that the SVC
only allows opportunistic bacterial
infections which then can kill the fish.
Mortalities may be 20-30% if supportive care
is given and the environment is optimized.
KHV kills upwards of
70%-90% of exposed fish which have not been
previously exposed to KHV.
Yes - Spring
Yes - Spring and Fall
Yes and No: The 'party
line' is that the virus had not formerly
been found in North America but there is
emerging evidence that the virus was indeed
being encountered in fish kills in Wisconsin
almost a decade ago.
Reported "absence" of SVC from American
waters may have been due to a lack of
testing. I personally (ELJ) think that
SVC is an endemic, and highly morbid
contributor to many of the Springtime
die-offs and illnesses we've seen every
year for the past two decades.
problem is that testing for SVC can
result in quarantine or worse. Retailers
are unlikely to "step up to the plate"
and endeavor to discover this virus and
limit its distribution.
Doubtful. This KHV virus
seems to be infecting "groups" of exposed
fish which go on to infect others, or simply
die off en masse. It's own virulence
(aggressiveness) is probably limiting it's
Pale white lesions may
result due to the co-infection by bacteria.
Fish may develop a pink or red color in the
skin as infection progresses.
Yes. Pale white lesions
may appear in the gills of affected fish.
Excess slime, especially on the head and
nape of the fish seems common. Body-color of
the fish may become blotchy and the internal
organs may be damaged or even liquefied.
People don't want to
submit for, nor do some labs want to test
for; SVC because of the maelstrom it causes.
SVC is an RNA virus and requires an extra
step when using PCR technology to diagnose
it. When the virus is not in a vulnerable
host or is not in its ideal temperature
range for replication, it's diagnosis is
The PCR test and the
other culture and swabbing techniques
available are quite accurate for infected
fish but false negatives can occur. When the
virus is not in a vulnerable host or is not
in its ideal temperature range for
replication, it's diagnosis is essentially
impossible. Diagnosing "occult" (hidden)
carrier-states of KHV may be impossible with
Fish often survive SVC;
but their carrier state is unconfirmed.
Survivors of KHV are said
to be clear of the virus and cannot be re
infected with KHV.
lack of virus in post-infection
specimens is probably due to the
difficulty in detecting virus in
asymptomatic fish or fish outside the
viruses' ideal range.
RNA virus, rhabdo
DNA virus. (Herpes virus)
Can be cultured, there is
a reverse PCR test for this virus.
Can be cultured, can be
detected via novel nucleic acid tests
(swabs), can be detected by PCR testing.
This morbid virus is
reportable by law.
This highly virulent
virus is not legally reportable and is as
Prevent exposure to the
Prevent exposure to the
SVC: If fish are
supported in ideal environments and
secondary infections are controlled through
aggressive antimicrobial therapy, including
antimicrobial food and injections, 70+
percent survival is possible.
KHV: Mortalities may be
kept below 70% if the fish are rapidly
warmed to above 80 Degrees Fahrenheit.
put the brakes on a late-summer
outbreak, you can let the temperature
sail down into the forties instead of
heating, and the losses will slow down
as the virus is deprived of it's ideal
temperature range. Fish may still die
from prior damage done by the
or later, the fish will have to be
an outbreak; if possible you can move
the fish as quickly as possible to
temperatures higher than 80 oF, or lower
than the seventies (in Fo)
| The real
issues concerning SVC are it's status as a
reportable virus. It's very possible that many
breeder and wholesale facilities (as well as many
residential ponds) have fish which harbor this
virus. Testing is currently possible, but is not
being undertaken on a widespread basis, because of
the cost, the lack of centralized and unified
regulation, and a reluctance of civilians, and
researchers to open that "can of worms". Retailers
concerned that their stocks could harbor this virus
would put themselves out of business by soliciting
SVC testing by a laboratory and receiving a positive
Fortunately, SVC isn't a terribly efficient killer
of fish and could be considered 'mild' at least
compared to KHV. Well-cared-for fish can often
survive the virus not unlike the way healthy people
survive the Influenza virus, and optimally housed
fish may not even break out with signs of infection.
I for one do not spend much time worrying about the
SVC condition because I would neither subject my
customers to diagnosis (and potential persecution
caused by an SVC diagnosis), nor would it change my
treatment, which is antimicrobial support "past" the
ravages of the virus . I am, as a healthcare
provider to fish, almost alone with this opinion
issues concerning KHV is it's predilection for a
narrow temperature range for infection, and it's
ability to hide when it's outside those temperatures
in asymptomatic (not sick) fish. If you grind up a
healthy-looking fish which you think might have or
be carrying KHV looking for virus, you can easily
miss the diagnosis unless the fish is actually
viremic. When a fish is symptomatic and sick with a
KHV infection, the virus can usually be cultured
into certain cell lines, detected by enzyme linked
PCR tests, or even detected by unique nucleic acids
in it's structure.
What it boils down to is this:
If you're considering buying some nice new fish this
Spring, how do you know the fish
isn't just sitting there; ready to explode with KHV
as soon as it hits seventy degrees Fahrenheit?
You don't have any security unless the fish has been
through the following cycle of cold-then-warm, which
are believed to be important triggering events for
the viruses ideal range in the seventies (oF)
allowing virus to replicate and damage the fish.
So, a fish which
has endured, and survived, a temperate (North
American) climate change from winter to summer could
be regarded as the safest fish to buy but does not
rule out that the fish could be carrying the virus.
Some dealers are artificially inducing these
cold-then-warm cyclic changes in their recent
imports to try and bring these cases out of the
woodwork before sale by chilling and then warming
the fish after importation, creating a "mini" cycle.
Testing for KHV can prove the fish to be without
the virus and "not currently infected" but since the
carrier state is a relative "unknown" at the present
time, there is little security in a negative KHV
test in a healthy fish. A negative KHV test in sick
fish could be considered much more reliable as most
fish with active infections have virus which is
capable of detection by available means.
Quarantine will become a necessity, not an
ideal, in 2003. This quarantine could arguably be
8-12 months to allow a complete "cold-warm-cold"
cycle in order to reveal occult KHV or SVC
|The following was
used on one of several cases of KHV which
broke out in the Fall of 2002. The fish were
being heated despite the onset of wintertime
temperatures outside, to support the fight
against what appeared to be a severe
bacterial infection. Then an Arkansas
laboratory indicated it was KHV. We had
stopped the losses initially with Tricide
Neo but the losses resumed a week after the
Tricide dipping which made us even more
suspicious that we were dealing with a
virus. (In quotes, my customer
Your losses have not been on par with the
others, most folks lose 70-90% of their fish
in a week or two. This is not a cause for
optimism. It may be because you used the
Tricide Neo it could also be because temps
were falling as they broke....
However, now most of the fish *are*
symptomatic and as the Arkansas specialist
indicated, you COULD let the heat off and
the virus COULD (should?) go dormant.
In the Spring, here's the possibility:
Since most of the fish are showing signs,
it's safe to say they are "viremic". If they
are chilled ***RIGHT NOW*** (today!) - could
they not chill down, stop the virus /
viremia / replication, and with warming in
the Spring, perhaps mount an immune
Yes, it's possible. Researchers I spoke to
know that we cannot re infect KHV survivors.
Did they survive the KHV with natural
immunity or luck?; or do they develop
specific immunity afterward, from incomplete
STOP HEATING NOW if the fish have KHV.
2) STOP the water falls; to prevent the
phenomena of "super cooling" from chilling
them too fast.
3) Maintain mid-water circulation to
maintain aeration and to de-gas the pond.
4) Remove dead as they show up.
5) In the Spring - when the Arkansas
specialist , you, and I have talked, we
should "accelerate" the heating process.
*NOT* letting them warm up slowly,
We should do a
sort of: "On your mark, get set, go!"
and move them as quickly and safely as
possible through the warming process,
for example, when water naturally hits
45-47 oF we could suddenly take them
"5-degrees-per-day" to a whopping, most
"KHV-unfriendly" eighty oF Six day warm
up. Window in the seventies: TWO
Crazy? Maybe. Kill all your fish? Not
like the virus probably would if water
temperatures were suspended in the
Finally, you *do* see the problem with
complete disinfection, "depop-repop"
plans. If you sacrifice all your
remaining fish, to get new healthy ones;
what on earth will prevent you from
restocking with 49 healthy fish and ONE
MORE KHV carrier? Nothing.
So I am not really in favor of a
wholesale depopulation at this time.
Erik Johnson DVM
When the pond was cooled, the
losses basically stopped. The fish became lethargic
and went to the bottom. A few of the worst fish
which were about to die when the water was warmer
continued to become sicker and died.
Some other fish were brought inside and rapidly
warmed to 80 oF, and made remarkable recoveries.
Spring 2003 is not here as of this writing but there
is some encouragement that if rapidly warmed, these
fish may recover.
It bears mentioning that it is
the professional opinion of most researchers and
ornamental fish health specialists in this field,
that in the interest of the health of our nation's
Koi and carp livestock, all individuals and
retailers suspecting that their fish might be
infected with SVC or KHV should request testing for
these infectious agents.
My (ELJ) position has been to recommend that
retailers and wholesalers decline SVC testing and to
destroy fish which might be infected. This
represents irresponsible behavior on the part of the
dealer and puts the hobby at risk because it will
hamper attempts to detect and eliminate the
SVC virus. However, the position is a result of the
There is no financial compensation
for lost livestock which may be
tested and slaughtered. You will not
be compensated for lost
business-days while under
quarantine. Requests to operate
under a new business name with new
brood stock and new production ponds
will probably be (and have been)
official process exists to formally
determine the length of impound and
quarantine. You may be under
quarantine for an indefinite period
There are no mechanisms to protect
your identity and you may be
informed of your SVC infection along
with the rest of the industry,
There is no standard format, nor
standard interval for testing of
your peers or competitors, so you
may be the only organization
subjected to the penalties
associated with reportable SVC