Koi Herpes Virus
This article is dedicated to my personal friends, Brenda and Charlie Atwell, whose pond contracted KHV and was essentially cleaned out, after re-introducing some fish which were returned to them after a breeding-loan.
The koi hobby has been rocked by a fearsome virus which everyone seems to be getting with their new fish lately. [2003 summer] This virus has been reported in Israel and among Japanese fish, but has so far not been diagnosed in its current form in Japan. There are active cases (and a few dealers) now in California, Ohio, Louisville, Atlanta, Chicago, New York, Indiana, Nevada, Arizona, Texas, Virginia, and Florida.
Understanding this virus, and what you can do to save your fish, is the intention of this document. It is EASY to save your fish from this virus with heat, at 87o F - if you are prepared, educated, and act fast!!!
Koi Herpes Virus is a virus infecting Koi which selectively penetrates and annihilates the epidermal cells of the koi, stripping the gills and skin and leaving them extremely vulnerable to secondary infection by Aeromonas and other fish bacterial pathogens. Most folks report almost total loss of their fish within 10-14 days, but it doesn't have to be that way.
Above, a Midori with typical gill lesions of KHV
Because of the way the virus works, the fish appear to be burned on the outside, or excessivly slimey as it's skin fights the virus. The damage to the gills is usually worse.
Koi herpes virus doesn't ALWAYS have to appear as mass-mortality (death) and wide scale infection. A case has recently come about that tipped us off to the fact that under the right circumstances, KHV outbreaks can look like routine Aeromonas ulcer cases with 10-20% morbidity. Losses (mortalities) in the case I am referring to were only 7-8% Additionally, losses in this particular case were completely stopped by heating the groups of fish to 87o F.
Here's a response from another person whose fish were heated to recovery:
"...I am done with the 3 day @ 87o. The koi that I sent you a picture of responded very well. Her back has kind of crusted over as well as some of the other very sick ones. I also heated up my 1,600 gal. facility. I have not had any more die with the sunken eye and sandpaper scales! (Although I have had some losses in small koi). Have you ever seen the koi change color under these temps ? I have one that lost her tancho, and a Sora-goi that went from a light grey to a very dark blue-grey."
Gill lesions are the safest clinical symptom to associate with KHV. What you would EXPECT to see are fish with red gills, however, there would be white patches or streaks in the gill tissue. Several recent cases however, had no gill lesions at all.
Diagnosis of Koi Herpes Virus can be undertaken via laboratories which are set up to perform PCR testing. This is "Polymerase Chain Reaction" testing in which tissues are homogenized and then a probe is used to find tiny bits of the virus DNA. This test can "miss" DNA particles which are present and in a good number of cases, there's not enough DNA to find. So false NEGATIVES may occur. However, when the test is positive, against the proper controls*, it cannot be a false positive.
*Some authorities are not using positive or negative controls and may be less careful about the preparation of the DNA probes. Cross reactions and false positives may occur.
How to get the diagnosis: Using a lab which is capable of performing the PCR test for KHV, you are well-advised to send at least three fish for PCR testing. For best results, these test-specimens would arrive alive at the lab, shipped overnight in good water, under pure oxygen. I have not seen a suspect-case yet which had sent three fish in which at least one fish was negative. This means that in groups of known-positive KHV infection, you have a one-or-two out of three chance of actually finding it. This is because the virus has a peak in its production during an epidemic (reportedly day #4-9) and when that peak is missed within a particular fish, then the fish is likely to test negative even though the virus is, or has been infecting that host.
Always send more than one fish, because among a group, there will be false negatives.
How Common is KHV?
KHV is extremely common. There are three reasons for this.
What Can Be Done About KHV Outbreaks?
This depends upon who you are. If you are a regulatory agency or epidemiologist, you might suggest destruction of all the fish affected to limit spread. This, however, would be a shame because you would end up destroying HALF the fish being sold in the USA right now. If a dealer were to destroy his infected livestock, he would be doing so while more than half the dealers in the industry bury the problem and continue to sell. Most of these, because they refuse to test even the fish with symptoms.
For example, Pam Kinkade bought fish from Barstow Koi and another koi retailer, both located in Newberry Springs, California. All her fish summarily broke with KHV and before she was able to heat the fish, she lost most of them. She contacted the two dealers, and Ken Liu of Barstow Koi immediately sent five fish to University of Georgia for complete necropsy and KHV testing. The fish came back NEGATIVE. No virus. Ken Liu of Barstow deserves commendation.
The other dealer in Newberry Springs California flatly refused to have testing done. Therefore, unless hobbyists are prepared to heat, and to heat quickly, they will buy from this type of dealer, and therefore stand to lose all their fish to KHV. Since, as I have illustrated, not all dealers exhibit 'due diligence' when confronted with this virus, HOBBYISTS are going to have to be ready to handle it when their fish develop this disease.
The best defense against KHV is a lengthy quarantine. In quarantine; heat, salt and Supaverm could be recommended but nothing but extended time can really exclude the virus.
The best defense against KHV is a lengthy quarantine.
In an outbreak - HEAT IS CURATIVE of the symptoms, (not necessarily the virus) but there are numerous difficulties.
For the hobbyist - when beloved fish matter:
I have saved just about every KHV fish I have been shipped by employing high heat and medicated food. Sometimes a person really loves a particular fish, or particular group of fish, so letting them all die is not a pleasant option. By heating, a person can save most of their affected fish, and continue to enjoy the collection as a closed "KHV Positive" collection. One advantage is that you can get all the free fish you want from the hundreds of cases across the USA - if you simply offer to give the survivors a home.
Heating fish has its drawbacks.
You must understand that if you heat a bacterial infection, the bacterial pathogen gets a metabolic advantage and accelerates its destructive path. The same is true for parasites. When you heat certain (if not most) parasites, they get a metabolic boost and proliferate explosively. So, if you blindly heat groups of fish to curb the obvious or latent KHV infection, you risk heating up another problem. But there are solutions to this quandary. Simply treating bacterial infections in the Qtank as you heat tends to limit the problem of accelerating a bacterial issue. Also, developing superior "shotgun" parasite regimens in heated facilities, or better still, using a microscope in these facilities, will prevent you from boosting a parasitic outbreak.
If you can diagnose or create a scenario without parasitic or bacterial threats, you are in a good position to "heat out" the KHV which may be carried by a group of fish, but there are two other variables.
Heating lots of water isn't easy.
The bucketwarmers shown above are forty dollars ar most tool rentals, painting supply places, or Lowe's. They can be variable in their power. The ones shown are 1500 Watts each. They occur in wattages up to 2000 Watts. As a rule of thumb, against a low outdoor temperature in a semi-insulated tub or vat, you would need one thousand Watts per two hundred gallons in order to achieve and maintain sufficient heat.
The thermostat is a Ranco Nema 4X Indoor Outdoor thermostat and is available from Grainger.
Wiring the paint bucket warmers to the theromstat is as easy as the diagram, but if you want to preserve the relative safety of having a "ground" (reduces chances of being electrocuted, which is a good thing), you will probably need an electrician to help you bypass the thermostat with the ground lead and let the thermostat just have the hot wires.
The second variable is the fact that warm water carries less oxygen, so while the fish are being pounded in the gills by this virus, they have less luck with breathing. Then, you get brilliant and start heating them up, further depriving them of oxygen for exchange. I respond thusly: If you don't heat them, they're goners. If you do heat them, expect some mortalities as the ones with the worst gills, and worst bacterial infections simply die.
Aeration in the heating facilities is SO VERY important! I prefer to use a water pump, set on it's side on the tank bottom. The discharge is aiming upward at the water surface. Done correctly, the surface of the tank will show a swell or slight floom as the water meets the surface and glides outward towards the tank sides and back down again. If you have the pump so powerful that the water 'geysers' upward, that's great - but it's your butt when the house mildews or the splattering geyser tips out of the tank onto the floor. [This happens the instant you head out to the store]
Here are the basic steps to rapid heating fish:
So, you saved your fish, what do you do with these survivors? Is it worth the pond keeping experience for 'the remains' of your former collection? Is it safe to get new fish? Can you show these fish?
When you save your fish from KHV, it raises all these questions.
I think people should save the survivors. How do you know that you're not going to go out, after killing off the stragglers, and buy new KHV infected fish? In the current climate, you do not know this. So you could kill the fish with names, just to repopulate with fish which could put you through this all over again!
I think keeping a smaller group of survivors has it's advantages in terms of their eventual growth. Underpopulated ponds are healthier, and the fish grow much larger in less time.
There are at least two ways to get new fish. You can heat the pond, and get all the new fish you want as long as the new fish are prepared for, acclimated to, and mixed at 87o F. I have mixed KHV and non KHV fish in a variety of circumstances and had ZERO transmission:
There are quite a few people who have mixed new fish in with their KHV survivors and NONE of them report any losses among the new fish. Now, that might be an issue for this year, and the statistic could change after a long cold winter. It could also be that the KHV survivors are truly negative, by either innate immunity or the heating process which might have saved them, or both. The jury is still out on that one.
I don't think a person who knows they have KHV survivors or KHV infected fish should take them to shows. The only reason so many people and dealers take KHV infected fish to shows is because they don't know the fish have KHV. YET.
I have a growing collection of "post-heat KHV survivors" at my home. I think they are great fish and they've been nothing less than perfectly healthy. When I want to add new fish, I simply heat the pond to a whopping 87o F and then add the intended new fish*. This is what it 'is' to be KHV infected in the aftermath. And I can live with it, happily.
*after a short quarantine and biopsy.