Koi herpes virus (KHV) Koi Herpesvirus (KHV) is a serious disease causing high mortalities and creating consequences for Koi that survive it. However, some comments about the disease in circulation are inaccurate from the scientific viewpoint and the speculation surrounding KHV is misleading to hobbyists who need to see the disease and the situations it creates in proper perspective. Diagnosis of any serious health problem does not happen in the pond and many suspected cases of KHV turn out to be other less serious health problems. Viruses are a fact of life all for all living things and  all Koi-keepers can do is minimise every possible risk not just of their Koi contracting KHV but any serious disease by quarantining new Koi irrespective of any previous quarantine or health certification. Why Suspect KHV? Whenever there is a problem in the Koi pond which causes high mortalities it is vital to explore all avenues before jumping to the conclusion a serious disease such as a virus is the culprit. Ammonia, nitrite, pollution by various toxins and parasites all have the potential to kill many fish very quickly. White spot, for example, is an extremely common health problem in newly purchased Koi.  A new environment particularly a temperature variation can trigger an outbreak of White spot even if the Koi were in perfect health when purchased. Bacterial gill disease also accounts for high mortalities. Only when all these possibilities are eliminated should KHV even be considered. What are the signs of KHV? KHV does not behave identically in all cases. The external signs can vary depending on the form the disease takes and how acute the outbreak is and the strain of KHV. In some cases infected Koi show no external indication of illness at all whilst others suffer skin changes including dry patches and severe gill necrosis. Commonly, nearly all infected Koi become lethargic, refuse food and exude mucus. However there are many reasons for Koi being  off colour , listless and taking less feed without there being anything serious wrong . Outbreaks of KHV commonly occur between 18-27C/60-80F and depending on water temperature and the form in which the virus presents the incubation period is 12-14 days. Mortality levels are usually high but this is not the case in attenuated outbreaks. How did my Koi contract KHV? There is a tendency to blame the last Koi purchased for introducing any serious disease but new Koi is not always the culprit. KHV can be carried by an asymptomatic Koi that has been in the pond for many years. This type of outbreak is triggered as and when conditions become conducive to the virus although introducing unquarantined Koi is a large factor in outbreaks as their health is unknown. Dealer quarantine is excellent when carried out to a high standard by biosecure dealers but alone it is not a sufficient safeguard. There is no uniform approach to quarantine unless the dealer is member of the Professional Koi Dealers Association and as cross - infective risks are greater in some trade premises a further period of home quarantine is recommended. Nowadays the potential for all health problems not just KHV is higher. Gifts of fish from a friend’s pond should also be quarantined, as their sources must be regarded as unknown. Seeing a fish in a friend’s pond for years does not mean that it is not carrying a latent disease. If an outbreak of KHV occurs and a fish has been acquired from a suspect source it may be advisable to place that fish in quarantine until the outbreak is fully investigated. Can it be cured? Claims have been made by hobbyists for a variety of “cures” for KHV but cure is not the correct word.  As with most viruses, drugs and chemicals have little effect and recovery is natural in fish that are able to mount a sufficient immune response. However, in some outbreaks it is possible to treat the secondary health problems that can complicate both diagnosis and recovery, such treatment can appear to those inexperienced with viral disease to bring about a cure when in fact the disease may be over anyway. Antiviral drugs may help to alleviate the disease but will not cure KHV. Antimicrobials and antibiotics may help with any bacterial secondary infections but are also not actual cures for any virus. How soon can I restock? Hobbyists are keen to move on after KHV and need to know how soon the pond can be restocked. Situations vary but in the case of a total wipe-out  drain the pond and power wash every surface and the filter thoroughly  and use a disinfectant product  in the cleaning process. The type or brand of disinfectant is of less relevance than the thoroughness of the cleaning but caustic soda and chlorine based products are best. Leaving the pond to dry completely after cleaning in sunlight is also effective. After thorough rinsing and possibly renewing the filter media if it is a type that cannot be cleaned properly the system can be restarted.   Include all pond equipment nets and bowls in the cleaning process. Survivors of KHV In cases where Koi survive KHV, they must be regarded as carriers and a decision made about their future.  Koi that survive KHV cannot live in the same pond as Koi naive to KHV.  However, survivors can be housed apart as long as they have completely separate equipment and the two ponds cannot ever share the splash factor when Koi are up to their usual antics. The decision to euthanase is a personal one for hobbyists that cannot house survivors and want to buy new Koi. In all trade premises stock surviving KHV should be humanely destroyed. Those hobbyists who want to keep their surviving Koi and do not want to euthanase them do not need to sterilise the pond. Carrier Koi must never leave the pond and any new stock must come from a specific chain of supply and anyone wishing to discuss this is welcome to ring LFH Laboratories to ensure that they make the right decisions for their hobby. Although a generalisation the closer Koi are genetically to the common carp the more likely they are to survive a viral disease such as KHV. Susceptibility to KHV depends on DNA and Koi, mirror carp, common carp and ghost Koi are all susceptible. However, a virus is a very complex pathogen subject to mutation and there are possibilities for viruses to survive in other host species even if they do not contract the disease. Such factors add to the difficulties for understanding let alone curing viral diseases. How can I know for sure my Koi have KHV? A Polymerase Chain Reaction (PCR) is used when Koi are in an advanced stage of disease and there are different types of PCR available. The drawback of this test is that it will be negative in healthy fish, as the test does not establish the presence of virus unless disease is actually in progress.  It is also possible that some Koi may prove unsuitable for testing for a various reasons. This makes the test unreliable as a tool in preventing the spread of KHV despite this fact it is still extensively used to screen healthy Koi around the world and this is unsatisfactory.  The ELISA test is used to screen for previous exposure to KHV as opposed to confirming the actual disease state and this achieved by looking at antibody titre. Like all tests, the occasional drawback with ELISA is the detection of other herpes viruses creating a false positive for KHV. There are several strains of KHV that add to the difficulties when it comes to developing diagnostic aids. LFH laboratories have been involved in projects aimed at improved testing methods. However, this research is costly and private funding from the Koi Industry is needed to support such ventures. Cost  is one factor but research is painstakingly slow by its very nature  and is  followed by trials and evaluations  which to hobbyists  add up to delay but this is inevitable. What is biosecurity? Biosecurity is not a single laid down list of rules and it is not just applied to premises as it also applies to the standards and practices of the operatives. It is a wide range of measures and procedures adapted to specific situations to minimise disease cross-infection. The level of control put in place to prevent the spread of all health problems has to reflect every risk factor within the Koi Industry in order to be effective and it has to be applied at every stage of the process of Koi farming and throughout the distribution network. Nowadays it is safer to purchase Koi from a dealer who is certified as biosecure. Why do we need biosecurity in Koi Keeping? When Koi from various sources meet, pathogens they carry are exchanged.  A pathogen is any agent that is harmful and includes parasites, bacteria and viruses. In most cases, both groups of Koi acquire the capacity to resist health problems carried by the other.  However, some diseases require specific incubatory criteria to be met before they materialise. Koi can be living together for many months before one group or one fish cross infects others and this  invariably clouds the issue as to which Koi was the carrier of a particular health problem. What quarantine measures provide the best protection? There are no foolproof measures against any disease and KHV is no exception, quarantine simply minimises the risks. Any additional measures that can be taken during isolation must make each new Koi a little safer. The use heat for most dealers and hobbyists is cheap and may detect problems before they can infect healthy fish. Tests by comparison are costly and are limited to specific diseases such as KHV and do not reduce general health risks.  Heat is very influential on the disease process but alone it is often not sufficient and a period of chilling is carried out before the temperature is raised to act as a trigger for latent diseases such as KHV. Heat Ramping Whilst outlining the role of heat ramping during quarantine it is not a scientifically proven procedure and Koi that do not develop KHV during the ramping can still carry the virus. However, what has been found during LFH investigations is that Koi that have been through a series of heat ramping sessions are statistically less likely to prove to be carriers when tested at a later date. In addition, using chill heat cycles revealed more cases of KHV than the control groups in which only heat was applied and far more cases than the Koi that were left at ambient temperature. The water temperature at the outset of quarantine will vary with the ambient temperature depending on the time of year but the need for heating equipment is unavoidable. The difficulties of achieving low temperatures in summer are obvious and for most hobbyists this means frequent water changes via purification equipment. One drawback is that Koi must be monitored to ensure parasites such as whitespot are not becoming a health problem. Many Koi naturally carry whitespot without any sign until a change in temperature acts as the mechanism that initiates an outbreak. What temperatures are required during quarantine? At the outset of the chill heat quarantine cycle the water temperature should be held at 15/16C for 24 hours then very gradually increased at approx I degree per day over approx 5 days to a minimum of 23C maximum of 27C and then held for 3 weeks. The  temperature should then be taken back down slowly to 15/16C for another 24 hours and again taken back up  to a maximum of 27C and held for another 2 weeks. If disease of any kind has not developed in that period, it is possible that the Koi have never been exposed to serious disease such as KHV but this is by no means foolproof. A recent infection is more likely to materialise but carriers do not always reveal serious disease after one cycle. Precautions and time scale The equipment used in the quarantine facility must be separate to that used for the main pond and hobbyists need to wash their hands after contact with the fish or water in either system. There is no time scale for the quarantine period as it varies with the ability to control temperatures and the health status and reaction of the Koi although 3 months is considered viable. On the day the quarantine period is finally over it is vital to ensure that the water parameters in the quarantine facility mirror those of the pond, the p.H and temperature are especially important. Having taken the Koi through a potentially stressful quarantine the move to the main pond must minimise the stress associated with any change of environment. The cautious way forward The disease we commonly term carp pox, which causes the unsightly shiny white tumours in colder weather, is scientifically termed Cyprinid Herpesvirus (CHV). Whilst a relatively harmless affliction as the name suggests it is also caused by a herpes virus, the most common type of DNA virus causing disease in fish. Prevention rather than cure is the best approach to all viruses in humans, animals and fish. The immunisation of all living things has many implications and human health is a major concern. Most fish production is destined for human consumption, whilst Koi are ornamental fish they are eaten in many countries including Japan and vaccinated fish are not allowed in the human food chain. Producing a vaccine is highly skilled and costly and has to satisfy international legislation. Certain types of vaccine can actually perpetuate the diseases they are targeted to prevent. This method has been tried and actually, spread rather than controlled Koi Herpesvirus. Raising antibodies in the immune response to fight any future exposure to disease is a common control method for viruses but it does not work for every type of virus. However, since the advent of DNA vaccines we can be more positive about controlling disease like KHV via immunisation. The role of vaccinated Koi in a pond. Although Koi that have survived KHV are carriers there is no requirement for hobbyists to euthanse them as they are pet fish. The legislation is naturally very different in respect of trade premises. However, restocking the pond with Koi naive to KHV is not a safe option and vaccinated Koi are then an alternative.  However in a normal healthy pond there is a risk with some vaccines that the disease can be perpetuated if vaccinated Koi are introduced although the incidence of this type of outbreak is low. Vaccinated Koi are allowed into the UK under legislation but this is not an indicator of the safety of the vaccine or the immunisation methods. Note  Koi Herpesvirus is now a notifiable disease. This means that it is a legal requirement that CEFAS a government agency working under the control of DEFRA are notified if an outbreak occurs and Lincolnshire Fish Health  automatically report all outbreaks  to CEFAS  when a test is positive for KHV.  It greatly helps the policing of KHV is those who have had an outbreak are able to supply all the sources of the Koi in the pond. Hope for the future Various projects are underway in the fight against fish disease. It is by continuous study we gain a long-term understanding of the disease process and the carrier state. At LFH Laboratories we are optimistic about many current research projects. However, we want to assure all Koi enthusiasts that keeping Koi remains a very enjoyable hobby when disease concerns are minimised. If quarantine is seen as the shared responsibility of dealers and hobbyists and an aspect of the hobby all concerns regarding serious disease like KHV would be greatly reduced. It is impossible in this summary to cover every aspect of any disease or address all the concerns that Koi keepers may have. In addition our understanding of diseases such as KHV changes as we learn more about it.  However if we can offer help or advice to any Koi enthusiast, whether dealer of hobbyist, please contact us.