Koi Herpes Virus is not new. It has been around for decades, even before we knew what it was. Koi were said to have a sleeping disease or some other explanation. In fact some studies of tissue samples taken over 20 years ago have been proven positive for KHV. But due to poor information, poor bio security and an over all apathy to the problem, KHV has spread to every koi producing country in the world. It is here now and here to stay, that is until a cure is found. But since it only harms carp and no domestic food fish crop is effected, there are no government grants and money for research is scarce. If you would like to donate or support this research, please visit the AKCA website.
There are many articles on the net about KHV and its effect on the koi hobby. Most are overly scientific and beyond what most of us are able to digest without a medical reference text. But basically it comes down to this. KHV is highly contagious and almost always fatal. Koi that do survive an infection are carriers and will infect others. There is still a lot we don't know about the virus and even our testing procedures are not 100%. We get false positives and more commonly, false negatives. And to make matters worse, the virus can go dormant for months, even years, spreading and infecting other koi, but never showing any symptoms until just the right conditions allow the virus to break.
The virus will spread from one koi to the next only when the infected koi is “shedding” the virus. By shedding I mean producing and releasing the virus from its body. It is possible for an infected koi to not be shedding the virus and not spread it to another koi. It is also possible for a koi to have briefly come in contact with the virus, develop antibodies to the virus, but never contract the virus. This is why 100% accurate testing is difficult to achieve.
There are two methods of testing right now. Serology and PCR. PCR testing is looking for an active shedding virus. Generally this is done by swabbing or scraping the slime coat, anus and gills of the koi. If the virus is dormant within the koi and not shedding, PCR will not find the virus and the test results will be negative even if the koi has been infected. PCR testing is generally used to confirm other test results, not as a primary test. The other type of testing is serology. This involves drawing blood from the koi, separating the serum in a device called a centrifuge and then having a lab test for antibodies to KHV. Unlike PCR, they are not looking for an active virus in the koi. They are looking for antibodies to the virus. When koi come in contact with KHV, their immune system immediately develops antibodies. But just because they have antibodies doesn't mean the koi have contracted the virus. Usually it does, but not always. The serology tests will measure the level of antibodies, a very high level generally means a certain infection. However a very low level may just mean is has briefly come in contact with an infected koi, developed antibodies, then went on its way never contracting the virus. Several retests must be done to make sure no increase in antibodies has occurred. If the level of antibodies increases in the koi on the second test, then it's a fairly safe bet that it has been infected.
Now, it's not all doom and gloom. You do have ways to protect yourself. First, always buy your koi from a dealer that knows and understands the issues of KHV. Ask about their testing and quarantine procedures. If they don't have any, then don't buy there. An experienced koi dealer should be able to rattle off a laundry list of quarantine procedures without blinking. You can also have the koi tested again before taking it home. A knowledgeable koi dealer should be willing to do additional testing at your request (and your expense). They can take another blood sample and have it tested for you. Usually cost for testing like this is $50 to $75.
But even the above is not 100%. Once you get the koi home, its always best to do an additional quarantine before allowing them into your pond.
KHV is a very serious issue in the koi industry. We must do everything we can to prevent further spread of the virus. No one country is infected, its everywhere and the only thing you do really do is protect yourself and your own koi. Nothing is 100%, but by following the best procedures you can greatly turn the odds in your favor.