Koi Herpes Virus (KHV). What is it?

The koi keeping hobby in the UK is served by a truly global industry. A combination of climatic, cultural and historical influences has lead to the vast majority of koi that are traded in the UK each year being produced and imported from abroad.

In fact, more fish fly into the UK each year than people to meet the demands of the fishkeeping hobby. Fish are exported from a small number of koi producing countries to the captive worldwide market, so that fishkeepers around the world can enjoy the delights of keeping ornamental fish.

Unfortunately, the exportation of koi and other pondfish around the globe also leaves the industry open to risks such as the transportation of disease and other health problems around the world. Although such occurrences may be unintentional, they can have economically significant and far reaching consequences which are ultimately the responsibility of our hobby.

Many of us, perhaps, feel it is our right to visit a koi dealer, expect to see thousands of colourful and vibrant koi displayed for sale, ready for us to inspect prior to making our purchase. Indeed, we can be quite disappointed if not disparaging of a dealer if they do not have the stock for us, by right, to purchase from their premises.

But stand back and take a view of the bigger picture and then perhaps such a view of the koi industry (of which you are an end-user) will change. Surely as koi keepers, we have responsibilities rather than rights for the koi that are at the centre of our hobby. If we want koi keeping to continue as we know it today, we will have to put the requirements of koi before our ‘wants’ or perceived rights as koi keepers.

We can often be guilty of regarding koi as simply ornamental objects of desire, each with its own price, rather than a living, breathing animal whose welfare we are legally responsible for.

The balance between our rights and responsibilities has been highlighted by the appearance of a new koi virus, Koi Herpes Virus (KHV) which has already been the cause of a number of health issues in the UK, leading to rumour and uncertainty at all levels within the hobby and industry. One of the causes of this uncertainty is the lack of factual information on which we can base our understanding of this relatively new virus, with rumour and conjecture flooding in to fill the vacuum. In order to put a lot of that rumour to rest, and to state what is known about this new threat to the health of koi, it is necessary to make clear what is fact (and can be verified) and what is not.

KHV – What is it?

Herpes viruses are widespread throughout the whole animal kingdom, and you are probably in the minority when reading this, if you yourself are not carrying a herpes virus. They cause cold sores and chicken pox/shingles and once contracted will remain ‘hidden’ in nerve tissue in your body until you become stressed, triggering the virus to multiply, producing the external symptoms associated with cold sores and chicken pox. KHV belongs to the same group of viruses.

If KHV is new, where did it come from?

It is not known for certain where KHV originated, but it was positively identified in Israel in 1998. This is not to say that this is where it originated, but this outbreak lead to the loss of a considerable number of koi and carp. As a virus is not a man-made pathogenic organism, it is both futile and narrow minded to try to cast blame or apportion fault to any individual, company or country.

The fact is that this virulent virus exists. We can only hypothesise how widespread the virus’ distribution might now be, particularly when considering the geographical spread covered by the movement and exportation of koi (and their water). Reportedly, KHV has been confirmed in Northern Europe, the USA and South Africa, and has been associated with fish from Israel, Japan and the USA (which could possibly have been infected with other stock after import).

How does KHV work?

KHV appears to be an immuno-suppressant, in that it inhibits a koi’s own ability to defend itself against other pathogens, particularly bacteria and parasites. Consequently, koi suffering from a KHV infection will often succumb to infections caused by bacteria and parasites.

The reported symptoms range from losing koi showing no signs of ill health through to more tangible symptoms such as bleeding from the gills, dry skin (where skin feels rough through the loss of mucus) and fin/body rot. However, it is important to stress that koi showing these clinical signs is NOT necessarily an indication that they have contracted KHV.

What about Quarantine?

Being a virus of course, means that KHV cannot be treated. Excellent husbandry and nutrition are likely to decrease the risk of koi succumbing to KHV, even though they will continue to be carriers. Furthermore, koi carrying KHV can infect other non-infected koi.

Due to the nature of KHV, quarantining a koi, even for say 8 weeks, amounts simply to an extended period of acclimatisation. Once a koi has been infected with KHV, it will always be a carrier and no period of ‘quarantine’ will rid the koi of a virus or remove its ability to re-infect other koi in the future. A lengthy period of acclimatisation will however reduce stress in new acquired koi, allowing you a better chance of managing its health.

Incidences where KHV has caused mortalities in koi have been when fish have been stressed and kept within a temperature range of 18-27oC, taking approximately 2 weeks to show clinical signs. It has been suggested that raising the temperature in a ‘quarantine’ facility over a 2 week period could be used to verify if koi are carrying KHV. Such a method could also produce false positive readings where KHV-negative koi have simply succumb to acute bacterial or parasite infections through the stress of temperature change.

Can I tell whether a dealer’s fish are KHV-positive?

The only test at present used to determine the presence of KHV is called a PCR test and is carried out by CEFAS (a branch of DEFRA, which itself used to be called MAFF). CEFAS have to date, confirmed 11 positive cases of KHV in the UK. CEFAS are keen to locate other incidents by sampling suspected occurrences of KHV in the UK. This will help them to determine the real distribution of KHV in the UK.

What can I do as a koi keeper?

You need to act in a responsible manner in all matters relating to this issue, and as koi keepers, we all have a most important role to play.

CEFAS and the koi industry need if possible, to be able to identify any koi exporters/producers that are KHV positive so that KHV-free stock can be secured for the hobby on a regular basis.

If you have any concerns about the health of your koi that suggests they may be KHV-positive, then as you should with any health problem, contact your dealer for advice. The only way that KHV can be confirmed is by involving the testing procedures of CEFAS. You should note though, that a koi that shows signs of KHV in a mixed pond of koi, may well have contracted it from other ‘resistant carriers’ in your pond that have not previously shown any clinical signs of KHV infection. These may have been bought from a different dealer who sold you the koi that is now showing signs of ill health. It would be helpful for your own peace of mind and that of a dealer if you kept records of the location and the date on which your koi were bought.

What Next?

The KHV issue is not about apportioning blame, as it goes a lot deeper than that. Just as we have all been involved in the curtailment of Foot and Mouth Disease, by driving through wheel washes and refraining from walking in the countryside (even though we were not directly involved in the livestock industry) we must take a similar constructive approach with KHV as we should with for any viral disease. By remaining pro-active and alert to the symptoms, and the methods available for confirming KHV, we can all work to avert this latest threat to our hobby.

As responsible koi keepers, we have our part to play in ensuring that dealers can continue to source healthy koi on our behalf, and we should be happy to play whatever role is required. Koi keeping is not our right, it is our responsibility.

Kill blanketweed and string algae.