KOI HERPES VIRUS

What to do if you suspect you have this disease.

An article by Paula Reynolds
Aquatic Patho-biologist & Epidemiologist
Lincolnshire Fish Health laboratories & Research Centre

Avoid panic measures
The diagnosis of any serious disease cannot ever take place beside a Koi pond. If the behaviour of Koi suddenly changes and heavy mortalities are taking place the hobbyist must not jump to conclusions. By process of elimination ammonia, nitrite, and pH swings should be investigated in looking for the cause. In addition toxins from pond construction materials or even rainfall must be considered as these kill Koi more often than is realised. Parasites are a frequent culprit and mucus smears should be taken from several fish to ensure that only a normal parasitic level is present. Only when it is established that none of these is a factor in the mortalities during a period when water temperatures are high is actual disease more likely to be the cause rather than an environmental health problem. Whilst Koi Herpes Virus is one possibility there are other diseases that create similar signs and behavioural changes in Koi.

Various signs
KHV does not behave identically in all outbreaks and disease signs vary depending on how acute the outbreak is. Some Koi have no external indication of a health problem whilst in other cases severe gill necrosis and skin changes are observed. It is the cellular changes internally that are one of the key factors in the diagnostic process. Commonly nearly all affected Koi become lethargic, refuse food, and exude mucus. Outbreaks occur between 18-27C/60-80F and depending on water temperature and the form in which the virus presents it can take 12-14 days or even longer for the infection to spread.

The diagnosis
In order to obtain a diagnosis of KHV it is necessary to sacrifice a fish for post-mortem examination. This ensures firstly that there is sufficient clinical information and pathological criteria for presumptive diagnosis of a viral disease before any virological investigation is initiated by CEFAS. Secondly it may save Koi if the examination reveals that KHV is not the cause and immediate treatment is possible. Thirdly is ensures that the resources of CEFAS are not wasted as KHV is not a notifiable disease and they are not required to take any action. Koi-keepers should appreciate that CEFAS does not research for the Koi Industry .The valuable work of this government department is to protect human health and monitor our waterways. It is the Koi industry that has to put its own house in order working in cooperation with DEFRA and CEFAS.

Testing for virus
After the post-mortem is completed and the presumptive diagnosis made Koi or tissue samples are subjected to a polymerase chain reaction test (PCR) by CEFAS. However the PCR is not sensitive enough to establish the presence of virus in all samples. Despite inclusion bodies clearly visible in micrographs, which strongly suggest a viral agent is the culprit, confirming KHV to be the causative pathogen is not always possible. Some hobbyists are unwilling to sacrifice Koi with a chance of surviving the disease which is understandable with pet fish and in addition the speed of death can limit the possibilities for examination and testing

Will all Koi be infected?
The mortality rate in most infected ponds is high although susceptibility to the virus depends very much on the genetic history and immune response in each exposed fish. Some Koi have a natural immunity to the virus and can appear totally unaffected whilst other fish around them are severely ill. The disease is highly infectious and if no new Koi have been purchased recently sharing pond equipment and hospitalising fish for those without the facilities to care for their own sick Koi are also possible factors. Dealers are asking hobbyists to make appointments rather than arriving at their premises with fish for examination or treatment because of the risk of cross-infection by the public.

Disease caused by Herpes viruses
Herpes viruses are the most common type of DNA virus causing disease in fish. Carp pox that causes the unsightly shiny white tumours in colder weather is scientifically termed Cyprinid Herpes Virus (CHV) and should not be confused with KHV. There is no treatment for Koi Herpes Virus and claims that various pond medications or cold sore remedies will cure it are false the resulting recovery from the virus is in fact a natural one. However, in some specific outbreaks remedies are used successfully to deal with any secondary health problems, which arise frequently to complicate both the diagnosis and the recovery phase. The name KHV has not been universally adopted and those who regard this disease not to be caused by a herpes virus favour the term KV.

Re-stocking the pond
Given the water temperature the signs of disease and the high mortality levels that many hobbyist have experienced it is likely that many outbreaks of disease have taken place that cannot now be substantiated as caused by Koi Herpes Virus. The vital issue having lost Koi to what is suspected or confirmed to be KHV is how soon is it possible to restock an affected pond. There is no straightforward answer as every situation varies and the following time scales are not accurate epidemiologically but are well within safe margins for the hobbyist dealing with disease in pond conditions.

In the case of a total wipeout in which immediate restocking is the aim power washing the pond and filter is advisable with either an iodophor disinfectant or a strong solution of potassium permanganate, often renewing the filter media is easier and safer. After thorough rinsing the system can be restarted and new fish introduced. However if time can be left to elapse before restocking an empty pond a month is adequate and then cleaning will not be required. If there are fish surviving and the vast majority of hobbyists will have survivors it is essential to leave the Koi to totally recover before introducing new Koi. Every outbreak will vary in respect of the virulence of the disease and influence of water temperature so there is no definitive safe period. In epidemiological investigations carried out at LFH over several years survivors are no longer infectious a few days after the very last fatality but there are risk factors and hobbyists are advised to wait one month after the last fatality.

The decision to euthanase
The decision to euthanase every fish following a viral outbreak in case of a future incident must be a personal one as there will always be unavoidable disease risks when keeping any animal and it is fact that viral disease never completely disappears once a pond has been infected. In our research ponds at LFH we have observed two completely different scenarios. Koi surviving viral disease live alongside Koi from all over the world known to have variable immunity to KHV however no disease outbreaks occurred in these populations after seven years exposure. However we have ponds in which further outbreaks have occurred. Those Koi surviving the first outbreak survived the second having all developed an attenuated form of disease but the naive Koi housed with them experimentally died of confirmed KHV. Some hobbyists choose to house post-viral Koi in a pond of their own with non-susceptible species such as Sturgeon and Orfe etc. In all trade premises the risks are too great and stocks should be humanely destroyed or housed elsewhere after a KHV outbreak.

Apportioning blame
There is a tendency to blame the last Koi that was purchased whenever a health problem strikes and this must be seen in perspective. Statistically outbreaks of KHV are more likely in newly purchased Koi. Recently imported fish pose greater risks due to the stress of transportation and environmental changes. Any disease can be carried by an asymptomatic fish this type of outbreak being triggered only when all the parameters are appropriate particularly water temperature. However what is not fully appreciated is that if the conditions are inappropriate for an outbreak of KHV a carrier fish can be absorbed into the fish community and may be responsible for subsequent outbreaks years later but never revealed as the culprit. Naive fish purchased since the original carrier can be the first to die and wrongly blamed for the outbreak.

In the pond already
It is a fact that some ponds are already home to Koi carrying KHV in which as yet no outbreak has occurred. There is no possible method by which such Koi can be tested as explained the PCR is not sensitive to latent disease in healthy fish stocks. At this time there is no action that can be taken that will help to minimise the risk of an outbreak.

The melting pot syndrome
Melting pot syndrome is my personal term for what is now happening to Koi because of their exposure to disease and the variability of both the innate and acquired immune response. They are nowadays exposed to any number of potentially cross-infective environments both before export and on arrival in the U.K. Koi are transported around a distribution network and held in premises with fish from worldwide sources, which makes tracking disease impossible. In research we have demonstrated that by exposing Koi to KHV in an attempt to establish immunity whilst the fish themselves do indeed develop a degree of protection it is possible that certain Koi exposed in this way can be the cause of later outbreaks and our epidemiological studies in this area continue.

Prevention -not cure
Many of the outbreaks of KHV that I have been involved with causing high mortalities occurred because quarantine was not carried out. Despite all the advice in the aquatic magazines to quarantine it still seems that the Koi-keepers favour taking risks. There are other equally serious diseases that threaten Koi besides KHV and quarantining should be an accepted aspect of the hobby for all serious Koi-keepers. Many dealers recognise that they can only partially acclimatise Koi and acknowledge that a period of quarantine with a naive companion fish from the pond is still the best possible way to safeguard existing Koi. The water temperature should be raised gradually into the range stated above and held there for three to four weeks. There is the risk that you may lose the fish in quarantine but your much-loved Koi will be safer.

Honesty
Having dealt with the misery that KHV can cause to hobbyists for many years I am sure that most Koi-keepers accept no dealer knowingly sells infected Koi. KHV is uncontrollable and no individual or company can be held responsible for the disease itself. However dealers are responsible for is the manner in which they deal with the public when they are suspected or confirmed as selling virally infected Koi. The hobbyist considers that the truth from any organisation or individual with whom they trade when livestock are lost is theirs by right and in my experience hobbyists continue to support the dealers who are honest about KHV and who offer them their cooperation and sympathy in the aftermath of an outbreak.

Quarantine & Acclimatisation

An article by Paula Reynolds
Aquatic Patho-biologist & Epidemiologist
Lincolnshire Fish Health laboratories & Research Centre

Prevention is better than cure
Failing to quarantine newly purchased fish is the major contributing factor in the introduction of disease and parasitic infestations into the Koi pond. Nowadays it is important to isolate all new fish due to the fact that the numbers of Koi being bred and reared intensively are indirectly creating an increased risk of all health problems. An increasing number of Koi- keepers are experiencing high mortalities, or the total loss of their Koi collection due to diseases of all kinds. Koi Herpes Virus (KHV) is a serious disease but Koi-keepers should bear in mind that there are other virulent pathogens that also have the potential to devastate a Koi pond. Quarantine therefore should be regarded as a vital aspect of the hobby and it can be rewarding to observe new Koi closely for several weeks in a tank before introduction to the pond.

The wrong word
The word quarantine creates inaccurate associations due to its use with other animals. In Koi-keeping terms quarantining is the isolation of newly purchased Koi during the phase in which recovery from stress and adaptation to a new environment takes place. This reduces the risk of latent infectious disease being passed on to existing healthy Koi, and lowers the risk of the new fish contracting environmental disease from the pond whilst at their most vulnerable.

Risk assessment
It can help hobbyist's appreciate the risks new Koi pose to existing fish by understanding why disease develops more frequently in recently imported fish. The immune system of Koi is challenged continuously by the various environments in which they live. Intensive fish farming techniques can mean overcrowding and dependence on chemicals to control disease rather than good husbandry at the producing farm. Inadequate preparation by exporters leads to poor conditions during a long plane flight. Once landed in the U.K the Koi take many trips around the distribution network before arriving at the aquatic outlet from which they will be sold to hobbyists. Some Koi experience more stressful events than other fish and some simply cope better. Whilst dealers specialising in Koi quarantine prior to sale the fact remains trade premises are naturally cross-infective no matter how well managed simply because fish live there and new stocks are constantly being introduced.

Biological cycles
We term the settling in period in any new habitat acclimatisation and no dealer can complete this long and complex process for the Koi he sells as they still have to be transported into yet another set of conditions after sale which triggers off the process yet again. Now add into this already challenging situation the fact that Koi having been uprooted in many cases repeatedly from environments in which they have started to establish and inevitably interrupted natural life cycles. Growth, development, reproductive potential can all be affected and Koi are vulnerable to parasites and diseases when the immune system is compromised. It is not always disease in the environment itself that fish succumb to. Koi may appear healthy yet carry disease sub-clinically and latent infections can also be triggered by environmental changes. Stress affects Koi internally increasing the level of hormones in circulation, if the level does not decrease as the fish acclimatises kidney failure can result.

The relevance of Temperature
Whilst temperature is not the only trigger of serious disease it is very influential. Therefore during quarantine gradually raising the water temperature to 68F/ 20C and holding it for a month will fulfil at least the temperature criteria for an outbreak of certain serious diseases including KHV. The potential for more serious health problems during isolation is obviously limitless. Ensure that all equipment for the pond is not shared with the quarantine tank or all you efforts at avoiding cross-infection will be wasted.

Companion fish
A companion fish that has lived in the pond can be housed with the fish in quarantine. If the new fish are carriers not showing signs of disease the companion fish being naive could succumb and the reverse is also true the existing Koi can be carriers of disease that the new fish are vulnerable to. Whilst this practice risks the companion Koi it is still far better than risking the entire pond.

Medication during quarantine
Initially allow the Koi to settle into the quarantine tank observing them to ensure normal behaviour and eating patterns. There is no need to use any medications against disease or parasites only intervene with chemicals if the need arises and a genuine health problem materialises. The water should be tested regularly particularly in the case of a new filter system. If flicking is observed this can indicate a parasitic problem if the water is tested free of ammonia and nitrite. Koi normally carry some parasites but the stress of movement is enough to scale up this level. The most common "after-sale" parasite is whitespot often carried sub-clinically, recently moved Koi should be observed for this infection. Resembling a sprinkling of salt on the body whitespot causes lethargy together with loss of appetite and kills if untreated.

Statistically speaking
There is evidence that some Koi travel better and are less stressed on arrival with a lower incidence of health problems when they have lived in larger water volumes. In addition when expertly prepared and packaged for export which is more skilled than is realised Koi arrive in far better condition. Larger Koi also fare better having the advantage of a more mature immune response wheras small Koi have a lower survival rate. This is not just due to their immaturity but statistically smaller Koi are sold and sadly end up in inadequate environments. All Koi have the same potential to develop disease despite their age, size pedigree, or price tag because the processing they all undergo can initiate health problems. In addition cross-infection with Koi from infected sources is a major factor in the spread of disease and this exposure occurs in all types of trade premises not just retail outlets.

Potassium dip instead of quarantine?
Dipping fish in potassium permanganate is often regarded as an alternative for those without quarantine facilities and this is a myth. No chemical on earth cures all known parasites or diseases and dips can be an additional burden to Koi still stressed by transportation. Dips in potassium permanganate strip the mucus layer, which disadvantages Koi living alongside fish whose mucus layer is intact, parasites and bacteria will find the new Koi a sitting target. Fish often arrive previously treated against parasites and over treatment can be a risk particularly to the gills of newly transported Koi. There are rare instances in which a dip is an option for a diagnosed health problem but no chemical is a substitute for quarantine.

My Koi died in quarantine
The principle of quarantine itself cannot kill fish. If a Koi dies during this period stress is the most likely cause with disease low down on the list of possibilities. Fish that die during quarantine may well have died irrespective of whether quarantined or not. A common fault is the size of the tank, which proves inadequate for the numbers of Koi it houses and larger Koi do need more water volume. If the tank is too restrictive this can increase stress instead of diminishing it. The conditions in the quarantine tank must be good and often the water quality is poor due to low-level filtration bacteria.

How long is a piece of string
There is no real answer to the question how long shall I quarantine as no one can quantify the potential risk carried by any one Koi. Many serious hobbyist's quarantine for a year whilst those opting for the middle of the road approach isolate for three months and those that live dangerously just a few days. Temperature has a major influence on disease development and seasonal changes naturally affect the life cycles of all fish pathogens. For example, the more harmful parasites that threaten the gills are active at spring and summer water temperatures and one month in quarantine during winter in an unheated tank may not be sufficient for such parasites to reveal their presence or even be eradicated by treatment. Disease may not apparent at low temperatures and if water is heated during isolation this will add to the length of the quarantine period. It may be months before the Koi can be introduced to the pond because of enormous temperature variation. It is vital to ensure that every pond parameter mirrors the quarantine tank before the Koi are introduced to minimise the adaptation the Koi have to experience.

Acclimatisation
The process of acclimatisation has two distinct phases, the partial acclimatisation achieved by floatation and gradual introduction of fish into the water of the quarantine tank or pond in which they will live. Full acclimatisation is a slower and far more complex process varying in how long it takes to complete from Koi to Koi.

Partial acclimatisation
Partial acclimatisation is carried out to minimise stress and Koi are floated in the bag in which they were transported and attention is focused on variations in the parameters of the water the Koi has travelled in compared with the quarantine tank. Water testing kits should be in use and any water chemistry variations such as p. H gradually adjusted by introducing a little tank or pond water into the floating bag. A thermometer ensures Koi are never released until the water temperatures are identical. The length of time this whole procedure takes depends on the initial water temperature and the results of all the water tests, it cannot simply be guessed as 10 minutes because it will vary with air temperature and other factors. Never leave a floating bag unattended especially in hot weather as oxygen levels can drop and always discard the water in the bag when the fish is released never pour it into the tank.

What a GAS
Following the initial introductory phase General Adaptation Syndrome (GAS) takes Koi through various internal changes as they get to know their new surroundings. For example, the p. H of both the pond water and the blood in Koi must equalise and the hormone carbonic anhydrase is either produced or withheld in order to maintain this delicate balance. The depth and size of their new pond is measured by sending out electrical impulses and processing the result via the swim bladder. Yet another new environment can be the last straw resulting in ill health or even death if acclimatisation fails. For the majority of Koi once health risks are minimised they are ready for life in the pond. This final move must be as stress free as possible the vital factor being how identical the water chemistry, temperature, and general conditions are in both the pond and the tank, thus ensuring this final environmental change is the safest the Koi has ever experienced.

It will never happen to me!
It is not the length of time that Koi are quarantined for that matters it is whether the Koi have fully acclimatised that is the real issue and this naturally varies fish to fish and cannot be quantified into a safe timescale. Quarantine is not foolproof but it does minimise the risk of all health problems. Hobbyists and dealers who dismiss the need for quarantine see health issues from a narrower perspective believing that fish are replaceable if the worst happens. For most Koi-keepers it is a sad experience to lose a whole pond of Koi to disease and the misery is made worse if the fish were family pets for many years. It is my experience that the negative aspects of the hobby are avoidable and those who opt for quarantine get far more satisfaction and pleasure out of keeping Koi.