Sourced from the Newsletter of Happy Koi - William Kelly, 23 January 2008

Forgive us if we ramble on about KHV yet again. It feels as if we talk about this subject a lot, perhaps too much. But we get a lot of phone calls regarding it and like Aids there seems to be huge ignorance about the disease. We also hear many variations on the topic and it was with some pity that yours truly missed one of the world's experts Ralph Knusel from Switzerland at a recent conference. We don't pretend to know everything about this virus, but here's what we do know.
As far as can be established KHV is a species specific virus that targets cyprinus carpio (latin speak for carp). This of course includes Koi, being the same species as carp! There appears to be some mutation of the virus manifesting itself in other species which is fairly crappy news but for now we'll assume we're dealing with the carp version of this bug.
It's a nasty virus that activates itself above 22 degrees Celsius. It hides in the flesh of the Koi at temperatures below this but only starts to replicate and become nasty when the temperature gets up to this level for around 10 days. Once it starts its story it spreads rapidly from Koi to Koi issuing forth death and destruction in short order. Primarily it causes death in over 95% of all Koi present in the water body at the time, although there are indications that this death rate may be coming down a little. Still for the last 10 years, KHV is one of the most successful Koi killers ever seen and will remain that way for the foreseeable future.
The virus cannot survive for longer than 24 hours outside of a Koi. It is water born which means it can easily transmit from pond to pond via wet hands, nets, bowls, birds etc etc. Fortunately it is easy to kill once outside of a fish. Chlorine will do it, as will drying out. In theory a body of water with no fish in it will also be rid of the virus within a 24 hour period but in our opinion that would appear to be a little risky – especially if you missed a little Koi fry or fingerling lurking in the depths of the pond…
Koi can be heat treated – raising the water to 30 Celsius appears to help the Koi overcome the virus. They will however become carriers of the virus for all time. Such Koi represent a Red Flag – and a Clear and Present Danger to all other Koi that they come into contact with. Our advice, tough though it is, is to euthanize survivors to eradicate this risk. In ten years time, you may have forgotten about the ravages of the disease and a KHV carrier may be released into another pond for the cycle to continue and wreak fresh trauma on some poor unsuspecting Koi and their hapless owners.
But we cannot dictate what you must or must not do. If it were us the choice is a no-brainer – we would heat treat and keep the fish alive. It is not the right thing to do, but that is what we would do without hesitation or question. These animals are our pets and that's just the way we are built. Which is why we go to the lengths we do to avoid being put into this situation in the first place.
Let us say that we do not believe that there is any shame in having KHV. If we ever get it we will make full and final disclosure and in the past when we have had a scare, we've made it known immediately. The name and shame policy is not one to which we subscribe – KHV can and will happen to any Koi dealer – but it is how this is handled that makes the difference.
For instance, we know of people who have knowingly sold KHV positive fish. This in our minds goes against everything we stand for. It is criminal at worst and morally bankrupt at best. We are not here to judge but to warn that this happens and we hear of it on a nauseatingly regular basis.
What we do judge is how the mess is handled afterwards. As Mark is fond of saying is there is a mess, we bring mops. If it is a big mess we wear rubber gloves. We clean it up. We deal with it and move on, hopefully learning from the experience. But we do not add to the mess. We do not package it and sell it. We do not spread it around.
Then of course after the tears and the trauma comes the rage and the human nature of wanting to get even. Sue someone!
After many years in this business we have never seen a case prosecuted. We think this is because such a case has not the faintest hope of ever standing up in any court. Think about it. A judge is going to ask you one thing only. Did you know that you bought a live animal?
And that we think will be the end of that. The next questions that might come up will be: Did you quarantine it? Did you test it for KHV? Did you check the KHV certificate that the dealer claimed to have had? Did you even enquire if the animal was KHV free?
It goes on. Even if, and we stress if, negligence on the part of the owner is not proved (not quarantining is negligence!) and the seller of the fish is proven beyond doubt to have sold a sick KHV+ve fish, the consequences of your loss of an entire collection of fish are not the concern of the seller. There is no legislation providing that sellers of fish have to guarantee your entire collection that I am aware of. Imagine that from a dealer's perspective. Imagine some new virus pops up out of nowhere and there is as yet no information about it? And this bug starts to kill entire collections of Koi – just like KHV did – would the dealer be responsible for your entire collection of Koi? No way – unless he sells you each fish for the price of replacing the collection!
At the end of the day one of my favourite sayings is that this is our business. It is your hobby. Your responsibility. Our role as dealer is to guide, assist, chat, empathise and provide you with choice. It is one of the reasons why we do not do Koi fish health consultations or provide maintenance services. We'd far rather empower you to be able to handle your pets competently and capably. This we believe grows your knowledge and grows the hobby.