Koi Herpesvirus (KHV) Avoid panic It is natural for every koi keeper to be concerned if their koi become listless and are not feeding normally. Taking panic measures is a common reaction particularly if mortalities have occurred. However, keeping calm and assessing all the possible causes for a change in koi behaviour or appearance is the best way to help the fish. Avoid unnecessary chemical exposure as it is safer to trace what is wrong with the fish before using any products. Check first Check the living conditions by testing the pond water for ammonia, nitrite, a swing in pH or KH, and a drop in the dissolved oxygen level. If a recent water change was carried out have chlorine and chloramine been eliminated? Check the pond for anything unusual such as leaves, berries, and blossoms. Plants and garden products can be toxic to fish and recent heavy or acidic rain can be an irritant. Consider if the odd behaviour in the koi began before or after a new item was installed in the pond or a product used for buffering the pH or for blanket weed, and has the pond filter had recent maintenance? Have new fish been introduced and are they also off-colour or is it only the original koi that are not behaving normally? Do the koi have excessive mucus on their skin and has this been caused by recent water quality issues or parasites? Take mucus smears if a microscope is available. Only when all the triggers of abnormal behaviour or change in appearance are eliminated should the disease be regarded as a possibility and, if KHV is suspected, panic measures will not help and there is nothing to be gained by moving koi. Caution with signs It is impossible to diagnose KHV by comparing signs in koi during a suspected outbreak with pictures of a confirmed case.  Koi can appear normal, exhibit slight changes in behaviour or appearance, and others may be obviously ill. There are now many strains of KHV and cases will differ. In addition, some of the signs seen during KHV are also observed during other diseases. On the Internet, there are sites that list signs that confirm KHV and such sites can mislead as virology is a specialised area. Possible signs Lethargy, loss of appetite, excess mucus, and sunken eyes, can be seen in a few outbreaks of KHV although it is equally possible none of them will be observed. In some cases, the gills develop grey patches which can indicate necrosis. However, this is not always present and changes to the skin only occur in some outbreaks. The water temperature is a primary trigger for an outbreak of KHV between 18-27°C /60-80°F although the virus can take 12-14 days to spread due to pond conditions. In large ponds and lakes, the incubatory requirements for KHV such as the water temperature might never be met and any carriers of the virus in residence might never trigger an outbreak. Diagnosing KHV A post mortem examination and tests on koi that are not going to survive provide the most reliable diagnosis. It is a fact that other diseases and conditions have signs identical to those seen during some outbreaks of KHV. It can be important to have KHV confirmed so the future of the pond can be decided. A polymerase chain reaction test or PCR is the primary diagnostic tool used for suspected cases of KHV. In simple terms this test is based on enzyme action that can trace specific genes. There are now many strains of the virus and more may emerge. Viruses have the capacity to mutate and change in order to enter new hosts and it is this capacity that makes their study complicated. Samples from fish in which KHV is suspected are amplified so sufficient material is available to compare with DNA sequences of KHV. This test confirms a positive outbreak and, if the results are negative, a new investigation is required if KHV is eliminated as the cause of the disease. Dealing with suggestions There are many claims made that cold sore remedies, large doses of Chloramine T, and lowering or raising the water temperature to extreme levels, are cures for KHV and these are all untrue. The use of anti-viral products in the pond is also not a cure although they can lower the cross infection level. Small frequent water changes will improve the water conditions as they can deteriorate during outbreaks of KHV. It can be beneficial to increase the water temperature to around 30°C/87°F and hold it for approximately 3 weeks. This is not a cure although heat speeds up the disease process so it is over sooner. This helps koi keepers as it is not pleasant to observe an outbreak and there are some benefits for any surviving koi that have been noted. The koi immune response The immune system in some koi is naturally stronger at fighting any disease and many will have the capacity to survive KHV depending on the strain of the virus and the severity of the illness. During a KHV outbreak, certain koi can appear seriously ill while others will cope better although this pattern does not always indicate which fish will recover. If a newly introduced koi is in the early stages of KHV it may well become a victim of the disease it is spreading. However, a carrier of the virus can live in a pond for years and not shed the virus until all the criteria are met and an outbreak is triggered. There are various situations in which KHV outbreaks occur that reinforce the fact that, in many ponds, the source of KHV might never be known. Carriers of KHV Survivors of KHV carry the virus for life which means they could infect any naive koi not previously exposed to the virus when the criteria are appropriate. No koi keeper has to euthanase survivors of KHV it is acknowledged that fish in private ponds are pets. However, surviving koi and others that have lived with them must live apart and all items of equipment such as pumps, nets, air stones etc. kept exclusively for use in the survivor's pond. Changes take place in surviving koi over time and their capacity to cross infect is a long term study at LFH Laboratories. However, it is impossible to know when change occurs in any fish and a virus is an extremely complex and unpredictable pathogen so separation for life is the best approach. KHV control measures Most serious diseases in fish are host-specific with some susceptibility existing in closely related species. In respect of KHV ghost koi as well as common and mirror carp can also contract  KHV. During an outbreak in a pond of mixed fish species, moving for example goldfish or grass carp that cannot contract KHV from the pond is not advisable as they could carry live virus.  KHV is now endemic in the UK and not all outbreaks are due to koi imports. The sale of KHV from unknown sources, koi auctions, rehoming unwanted koi and even gifts of  koi can spread the virus. Cefas, an arm of Defra, has to be informed of outbreaks of KHV although they do not visit private ponds. In trade premises, after a KHV outbreak, Cefas ensure all koi that pose any risk are humanely euthanased and the facilities sterilised. Hygiene after KHV When there are no survivors or they have been euthanased and the pond is to be restocked, cleaning is vital. The KHV virus dies quickly in an empty pond, however, due to the nature of viruses, certain elements can be left behind. Thorough cleaning of the entire pond and filter system should include either the use of caustic soda, or an anti-viral disinfectant.  Renewing the filter media if possible and allowing the pond to dry in the sun are also measures that will help.  It is important to include pond equipment in the cleaning such as pumps, nets, bowls etc.  The pond must be rinsed thoroughly before refilling with water and both chlorine and chloramine removed before restocking with new koi. KHV antibodies It is possible to test healthy koi to see if they carry KHV and could trigger a future outbreak. However, this type of test differs from the PCR test used for live active KHV and many factors have to be considered before such tests are carried out. Testing individual koi cannot reflect the health status of other fish living in the same pond. The only way to know if a whole pond is totally KHV free is to test every koi which is impractical. This is the reason why antibody tests are usually carried out in very specific situations. There is no laid down protocol for such tests and many different methods are in use. Situations differ for dealers compared with koi keepers as fish suspected of being KHV carriers can range from a highly prized valuable koi to a much loved pet koi. KHV still exists It is a sad fact that KHV is in farms in many koi producing countries. It is difficult to control a viral disease no matter how assiduously eradication is attempted.  Whilst the level of KHV in imported koi has decreased, there are still insufficient safeguards in place in many koi producing countries to prevent carriers of KHV or koi going through the virus arriving in the UK. In most koi farms it is vectors such as birds that spread the virus from one mud pond to another and other wildlife can also play a role.  The erection of fencing and netting to keep the birds out has some degree of success although the close proximity of farms is another factor. The location can make a difference and, in eastern Europe, one farm has been able to certify their koi production free of KHV and other viruses. In the UK, English bred koi are also a safer option. It is unlikely KHV will be spread by birds or other animals in the UK. A bird would need to visit a pond infected by KHV and, soon after, find a healthy pond in order to pass on the virus. Not only are such opportunities remote, the immune response in a bird will kill off an alien virus on its body as birds cannot host fish viruses. Koi dealers There are drawbacks for aquatic outlets and koi dealers in having to put koi through an extended quarantine period since many do not have adequate facilities. In some premises, new koi are sold within a day or two of being imported. This is far from ideal and not only in respect of KHV. However, it is a fact there are no standard practices for dealers in the UK and few are able to follow a recognised quarantine protocol. Most well established koi dealers buy koi from the safest farms due to the concern KHV creates throughout the hobby. Aquatic outlets not specialising in koi may be less aware of the facts regarding KHV and that is where those new to the hobby go to buy koi. KHV was in the UK for many years before it was acknowledged and it continues to damage the hobby and the trade. Some koi enthusiasts end up caring for KHV survivors with all the precautions required and others fill in their ponds. For the trade, a KHV outbreak is serious as customers need to buy koi with confidence and dealers often have to bear the cost of their losses. Keep aware Carriers of KHV could be on sale or in circulation in other ways for some time to come.  It makes sense to purchase from a dealer whose methods ensure the risk is as low as possible. Dealers naturally advertise their koi and may be accurate at describing the good skin quality in the koi they sell. However, claims made by a few exceed what is scientifically possible when it comes to KHV free koi. I see the sad reality of KHV in my laboratory and, if the risks are understood, the disease is avoidable.