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Koi Herpes Virus

Keywords: Koi, Goldfish & Pond Health Koi Herpes Virus Symtpoms Signs Cure Control Prevention CNGV Koi Virus Diseases

Koi Herpes Virus is a common virus of Koi which attacks the surfaces of the fish. This includes the surface of the skin, the surface of the gills and the surface-linings of the fishes' kidney. It doesn't affect goldfish.

It spreads from fish to fish very rapidly and kills most of its victims in a few short days. In water which is about seventy five degrees Fahrenheit, Koi Herpes Virus will kill 90% of affected fish in a mere four to six days. The virus does not "hide" in fish unless the fish is naturally immune or unless the fish is in water which is cold, under sixty five degrees Fahrenheit. If the fish is susceptible to KHV it will show symptoms and be sick if the water temperature is in the mid to upper seventies.

If you raise the water temperature to an extremely warm temperature, the virus dies in the fish. This is not unheard of among viruses because they are actually unstable pieces of DNA which require cell contents and an optimal temperature range to live. What is unique is that many Herpes viruses affect warm blooded animals - you cannot materially change the body temperature of a warm blooded animal. The fact that we can heat up a cold blooded fish to temperatures which would be considered extreme by their own natural history is an asset in the control of symptoms referrable to KHV in Koi.

So, many people are aware that heating Koi at a rate of ONE degree Fahrenheit per hour until the affected fish are in water which is at 86 Degrees Fahrenheit will control the mortalities [deaths] among KHV fish. It is imperative that when you warm up KHV infected fish that you control co-morbidities and increase aeration to the point of overkill. Detailed documents exist at "www.koivet.com" about how to accomplish this and how to control co-infections.

After heating up a group of fish and saving them from Koi Herpes Virus, are they safe from re-infection and can they cause infection in other fish? Neither answer is known.

Koi which are heated and saved from Koi Herpes Virus are usually susceptible to re-infection because it takes up to thirty days of exposure to create antibodies in Koi. If the fish are heated early in their infection, the virus will not have been present in the Koi bloodstream long enough to make them immune. After successful heating, there are NO cases wherein closed collections of fish were re-infected by "carriers" left behind by heating. Always, new infected fish are introduced to these collections. All of these notes are anecdotal, meaning they were not validated by scientific measurement.

Therefore, all heated "survivors" SHOULD BE CONSIDERED INFECTED AND INFECTIOUS until proven otherwise.

Since most people who suffer through a KHV outbreak have survivors, and since there are many of us, the dilemna then is: "Should I get new fish and put them in with my KHV survivors?"

Many people have mixed new fish with KHV survivors without sacrifice. And there have been no infections from the survivors but the statistical group is small and there have been no controlled studies. Other people have killed all their KHV survivors, and for some retailers this has meant the death of hundreds if not thousands of fish.

 What to do with remaining fish?
Remaining fish should either be destroyed humanely, usually by anesthetic overdose then freezing. Alternatively, there are many people with small collections of KHV survivors who would add your fish to their collections, having already been through KHV and not fearing a relapse if they have engineered heating systems. One of the problems with eliminating all your survivors and buying all new fish is that you have a ten percent chance of buying NEW fish with KHV infections, so there's no guarantee that you can restock without returning to square-one again.

- What to do with your pond
The virus is VERY unstable outside the fish. If the pond is left without ANY fish host for 3 days, the virus is considered by most experts to be "gone". If you're not one to take any chances, double dose Chloramine T or double dose Potassium can be deployed in a fishless ecosystem and the virus will not survive it. Clorox at a dilution of 1:30 is MORE than enough to sterilize the virus from a contaminated retail tank.

- How long to wait for new fish
Since (odds against you) any new fish you buy theoretically have a ten percent chance of being infected with KHV (especially if they are from Taiwan, Thailand, Malaysia or SriLanka, and (odds for you) since the virus is not likely to last long in the pond ecosystem without a fish host, a week "without fish" would be a safe recommendation, plus or minus the additional safety net of the sterilization tecchniques mentioned above.

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