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Koi Herpes virus



Koi Herpes virus (KHV) is the most deadly disease threatening koi today. KHV was first describe in Israel in 1998, but apparently the disease was documented in Japan several years before that. KHV is suspected to be present in koi populations from many countries, and current evidence suggests that when purchasing a new koi, no county of origin should be considered free of the virus. Although called a “herpes” virus various views exist amongst scientists whether it is herpes virus or not, but for us mortals that are only interested in keeping our collections safe, it hardly matters. What is important is that when the virus strikes, it first of all undergoes a short period of incubation. The first mortalities occur after about seven days. However within two to four more days, mortalities rise sharply and can reach 90% or more. This may vary depending on water temperature. Disease caused by KHV is generally seen between 20 and 29 degrees Celsius. The virus infects the epidermis (skin) and gills of the koi, effectively nullifying the defence system of the fish against disease, and damaging the gills to such an extent that the osmotic integrity is compromised.

   happy_one_moment    khv_deaths
   Photos supplied by Brett Southgate

When a Koi have been exposed to KHV, four possible things may happen. The fish is:

• Not infected, which means it is naturally resistant or immune to the disease.
• Infected and die.
• Infected, but survive and eliminate the virus and do not become a carrier of the disease.
• Infected and survive, but become an asymptomatic carrier. Asymptomatic carrier fish contain viral DNA that can become active some time in the future and can spread the infection to previously unexposed fish.

There is clinical evidence that suggests that KHV do not infect goldfish, but it is not known whether or not goldfish can be carriers of the virus or not.

Symptoms associated with KHV.

1. Affected fish will appear sluggish/fatigued, followed by death.
2. In the interim period white patches of dead tissue may appear on the gills and the skin.
3. This results in these superficial cells to die and the infected fish exhibits excessive mucus shedding, dry “sandpaper” skin, dead gill cells.
4. Often attacked by fungus, parasites and bacteria
5. Lethargy and weakness.
6. Head down swimming.
7. Sunken eyes, darkened skin and ulcers.
8. The fish may also swim erratically and may exhibit spurts of intense activity, interspersed with the aforementioned sluggishness.
9. As the skin dies away, affected koi do not eat, cannot breathe, and die a slow, painful death over many days.
10. KHV is often associated with a cocktail of parasites, fungus and bacterial infection.
11. Although the above symptoms may appear in your koi collection, here in South Africa the only reasonably sure way to determine whether it is indeed KHV is to have it tested at Molecular Diagnostic Services in Westville, Durban.

Prevention of KHV

1. Quarantine is the best defence against KHV at this time. The quarantine should follow a protocol of exposing new fish to the optimum temperatures of between 20 and 26 degrees Celsius for at least three weeks. A much better period would be three months. The longer the quarantine period, the more likely infected fish will be revealed.
2. If the fish do not display any symptoms during this time, it may still be a carrier and a non infected fish should be added to the quarantine tank.
3. Most commonly, infection is via a new fish that is added to the pond without proper quarantine, so quarantine is essential.
4. It can also be spread through infected equipment, or (maybe) water. Sound bio security must be established and maintained. Some dealers go to the extent of disinfecting the shoes of employees when they leave the quarantine area.
5. Stress (including transport, parasites, poor water quality and other factors) probably plays a role in causing fish to breakdown from the disease.

Treatment of KHV

1. There is no cure or treatment for KHV infection at this time.
2. Treatments such as Potassium Permanganate or treatment for secondary bacterial gill disease, fungal and parasite control, antibiotic treatment for internal secondary bacterial infections, salt for relief of over hydration, or vitamin C for immune support may help koi overcome secondary problems, but this does not mean they cure KHV disease.
3. At temperatures below 18 degrees Celsius, koi generally do not die or show symptoms of KHV infection.
4. Infected fish will develop signs of KHV disease when the temperature reaches the optimum temperature for this virus of between 20 and 26 degrees Celsius. Raising the temperature to 30 degree Celsius may increase the number of survivors.
5. Surviving koi must be considered to be carriers until proven otherwise, and therefore, should not be shown, sold, or transferred without advising the new owners that these are KHV survivors.
6. If KHV is confirmed, depopulation is recommended.

Can we ever win the battle?

I have had the terrible experience to witness an outbreak of this terrible virus only once.It happened in a friend and client's pond. Rest assure, nothing can prepare you for the real life experience of a KHV outbreak. What you learn in all the studies and descriptions about the symptoms associated with KHV can at most, only be regarded as very general indications that the virus is present. Not all Koi will exhibit the same symptoms. The symptoms were the following:

The first fish, a Midorigoi that showed symptoms, became lethargic/fatigued and stayed on the bottom of the pond with fins spread. There was no rapid gill movement.  One circular black dot, one centimetre in diameter appeared below the lateral line.

Next day, the Midorigoi remained at the bottom of the pond and developed black blotches all over the body, with smallish white clumps of slime on the head and dorsal area. The fish resembled something prehistoric. Also on the second day, more fish became lethargic on the bottom of the pond. No parasites were found on any fish. Salt and Acriflavine were added to the pond.

In the course of the next week, more than half the collection started to show a variety of symptoms, while some fish died without showing any abnormal behaviour. The symptoms showed were the following:

Heavy mucus excretion
Rapid gill movement
Spiral swimming
Fish will stay at surface of the pond with dorsal fin and upper part of the tail fin above the water.
Lying at the bottom together in groups
Mad dashes around the pond
No symptoms at all
No symptoms and still dying
In the latter stage of the infection, fish will weakly lie on their sides with gills barely moving and the occasional tail movement
Redness of the whole body, gill plates and fins
Deep red gill filament
Bleeding from the gills
Blood oozing out from under the scales
No visible ulcers
Accumulation of fluid in the scale pockets
Dry patches where scales have died and feel like sand paper
Sunken eyes
No fin erosion
Internal bleeding
Yellow mucus-like fluid in intestines, running from mouth when fish is lifted out of water
Tetrahymena found amongst gills of almost every weak fish lying on the bottom of the pond
I have not seen the notch on the nose or grey streaks of gill necrosis in any of the cases. The only common symptom that I have witnessed in deceased Koi is that the gills were severely damaged, dark red and covered with a jelly-like mixture of dark red blood and mucus.

khv1               khv2

The photos above are self-explanatory and consistent with the symptoms as explained. Please note the  yellow mucus-like fluid that oozed through the mouth.

khv3              khv4

Dark red dammaged gills and internal bleeding. The internal bleeding was maybe due to secondary bacterial infection.


Note the dark colouration, white patches of mucus and the sunken eyes

I would like to repeat, not all the symptoms will be present in a pond infected with KHV. In fact only a few symptoms may be visible and the symptoms may for a time be very subtle, often resembling a normal parasite infection. Only very resilient Koi will develop ulcers. The infected fish die so quickly that there is hardly time for ulcers to develop.

Regardless of the symptoms, if tests show acceptable water parameters and fish do not respond to conventional parasitic and bacterial treatments, test immediately for KHV.

One can just read the two KHV articles in Koiquest and Fish Helpline to realize that KHV is here to stay. With the recent (2009) outbreaks of KHV in South Africa, every Koi keeper and dealer will have to undergo a paradigm shift regarding quarantine, to protect their Koi and the Koi of others from this terrible disease.

Spike Cover was involved in Project KHV in the USA and is also the author of the well-known KHV Fact sheet. My question to Spike was the following: “Do I understand correctly that a carrier can escape detection by the lab tests and only surface years later when a stressor triggers the virus to become active again?” This most disturbing reply regarding KHV was received back:

"There are things we don't know about this bug.  We don't know for sure where it hides when it's not causing active disease.  We don't know what triggers it’s re-emergence to "awake" and cause disease.

Some of the clues have been provided by various observers and researchers around the world (the following is from memory and if it's not completely accurate, it's close):

• Sven Bergmann in Germany has found the viral DNA in blood (white cells) for, I believe, up to a year PI (post infection).
• Lin Jin of Oregon State University (USA), found viable virus (in unspecified tissues) of healthy fish that were past one year post exposure (we don't know if they contracted the disease initially or not)
• Some Japanese investigators have found KHV in river water, I believe something like several months after the apparent cessation of the active disease in carp in that river.
• Researchers in Weymouth (England) found that non-cleaned filters from systems that contained fish with active disease could infect naive fish for up to two weeks after all disease fish were removed from the system.
• Hobbyists in Atlanta Georgia (USA) had a KHV outbreak in the summer (late June-early July), heat-treated (86°F) the diseased fish, many survived.  However, naive fish placed in the pond broke with KHV the next spring.
• Sophie St-Hilaire et al have authored two papers in which she and the others showed that survivors can re-break with the disease.
• St-Hilaire et al and Adkison et al and others have found that some (tho apparently not all) survivors develop antibodies to KHV and that (ELISA) tests for the presence of these antibodies are possible (both Weymouth and U.C. Davis offer such tests).
• Bran Ritchie of Univ. or Georgia (USA) developed a serology test for inferring the presence of KHV antibodies - the test shows if dilute serum from suspect fish will inhibit the the growth of KHV in a culture of Koi/carp cells.
• Both the (ELISA) antibody tests and the serology tests have been used to detect survivors of past KHV infections with the inference that fish that test positive are very likely carriers of the disease.

All this provides clues but we still don't know if the disease forms a true latency, i.e., sticks its DNA into a cell and waits for a later opportunity to replicate and re-emerge as a complete viral particle and cause trouble, and/or forms a persistent low-level infection (the entire viral particle replicating very slowly) that goes unnoticed for a time then resurfaces as full blown disease.  We know that the disease usually appears within a specific temperature range, but researchers in Europe have shown the disease may be adapting to lower temperatures.

Several years ago the Israelis "made" what they called "naturally immune fish" (or NIFs), by intentionally exposing Koi to KHV then heating them to 86°F for a time - I think they did this twice then sold the survivors as "NIFs."  It has long been suspected that this was a recipe for disaster in that they were thought to be producing carriers that were, in fact, ticking time-bombs.  That may be at least part of what we're seeing now.

Then there's Kovax in Israel that has been 6 months away from introducing their KHV vaccine into the USA for over two years now .  They report something like 87% effectiveness from their injectable vaccine.  Who know if and when we'll ever see that vaccine?

It's all encouraging and frustrating at the same time.  The more we can learn about this disease, the more likely we are to be able to defeat or at least control it."

Duncan Griffiths is the author of the comprehensive Koi health book, Step By Step Advanced Koi Diagnosis & Treatments. The same question was posed to him: “Do I understand correctly that a carrier can escape detection by the lab tests and only surface years later when a stressor triggers the virus to become active again?” This is the comprehensive reply that I have received:

"They may become carriers – but do these carriers only infect other Koi which have never had KHV or do they infect Koi which are also carriers? I.e. left over from another collection?
Yes and yes. A survivor, any survivor, has the potential to be a carrier and it seems a survivor from a KHV outbreak may or may not survive the next outbreak. It’s a lottery. There are no hard and fast rules to this. It seems the more we learn about this disease the more we still need to learn, such as, where this bug hides in the body awaiting its escape. That is one burning question. The other question science has yet to answer, is how long it will survive in hiding. We know so much about this disease, but on the big questions, we still need answering.
Being as KHV is a herpes virus, the best we can do is treat it like any other herpes virus until science says otherwise, and that is namely that is once you have a herpes virus you have it for life.  If you have had chicken pox you have it for life, if you have herpes you have it for life For example, shingles is chicken pox’s second attempted breakout and this can be after countless decades.
If you proceed like this you won’t go far wrong we do not know what the carrier status is in specific terms.  But if you class any fish that has been exposed to KHV as a cottontail carrier based on the above again you won’t go far wrong. Or if a Koi tests ELISA test positive for KHV antibodies, it’s either:
A) Been exposed to a viral outbreak and survived or
B) Been vaccinated against KHV. A Koi has to be exposed to KHV vaccine or the disease to form antibodies against it. It is that simple. ELISA cannot determine if it’s the disease or vaccination, or a vaccination has been given, or the vaccination has been certified as given but it was given to mask an original natural exposure   to the disease.
The example below had Koi in quarantine for a year and obviously a latent KHV infection. Everyone was happy. But the KHV may have been triggered by the handling and transport – stress.
Quarantine is useless unless you do something with it, if you keep a Koi in quarantine for a year on its own or without stressing it, what have you learned? ZERO! What you do with quarantine is as important as the quarantine itself. Your fish will have bacteria or god forbid other stuff that the new fish are maybe naive to and the new fish will have bacteria you existing stock are naive to. We have to put this into the melting pot to see what breaks it’s better contained here than the bomb goes off in the main show pond.
Proceed by ELISA testing all new stock and if you value that new stock, your existing stock also. Or heat ramping all new stock with known naive stock (Koi not goldfish). Follow an exact heat ramping and lowering protocol through at least three cycles. That should do it. It is not 100% but the best you can do if resource is tight
Mickey of Yumekoi ELISA tests every single fish that he imports and certifies all his fish. He keeps shipments separate so if one does test positive he has that batch contained. This has paid off a couple of time for him and he can also nail the Breeder for compensation cuz he has the paperwork to back everything up. This regime adds around £20GBP on every fish."

So, there you have it. There is a big debate and finger-pointing in the October 2009 edition of KOISA about who should accept responsibility for the recent outbreak of KHV in South Africa. I would like to quote a few paragraphs from a recent international debate and information sharing between heavyweights Chris Neaves, Duncan Griffiths and Spike Cover, that I had the privilege to witness. The debate centred on KHV and later on addresses the consequences of going public and attempting to trace the source. In conclusion I would like to quote some selected paragraphs received from the well-respected Duncan Griffiths during the debate in this regard: 

“It’s a complete waste of time and effort trying now to find where the carrier came from for various reasons not least of which because:

It only takes one carrier to start a KHV outbreak but that one carrier need not have been the only KHV carrier in the pond, there could be multiple carriers introduced at various points in time.

The carriers could have been in the pond for years. It could have been in the pond  for five minutes. You have no way of determining this. People have an auto response (understandably but wrongly in my view) a lot of the time to blame the last Koi in the pond and therefore that supplier)

So at this point it’s futile to try. It will spread ill feeling and suspicion  with no decent evidence.

 If you really want to find out chapter and verse  and even this would not be 100%,  this  has to be done before any KHV outbreak  and would involves Elisa testing the whole  population  for KHV antibodies provided none have been vaccinated against KHV , when the results come back this will show the positive  KHV subjects  that have been exposed  to the disease  and therefore the breeder if known and the dealer who supplied.

.., last but not least,  instead of wasting time looking for the breeder / dealer, remember the fact that  quarantining  and screening is the  buyers responsibility  as well... even if the dealers is a good dealer that does  some of the above  this is not an excuse for  avoiding quarantine at home.”


Last Updated on Tuesday, 07 September 2010 20:38