The Facts about KHV - Koi Herpes Virus

The recent appearance of the Koi Herpes Virus (KHV) has lead to many rumours within the hobby and the koi industry. A cause of these rumours is the lack of proper factual information, so to put them to rest we must clarify what is actual fact. Herpes viruses are widespread in animals. They cause cold sores and chicken pox/shingles, and once contracted may remain dormant in nerve tissue until stress triggers the virus to multiply, producing the external symptoms of these illnesses.

Every Year there seems to be considerable health problems occurring with Koi collections all over the country, this usually starts in spring and may continue throughout the summer, this year has been no exception.

The buzzword banded around has been ‘virus’ and new, undiscovered ‘bacteria’, which have apparently been wreaking havoc with Koi collections both old and new.

It is true that there are both good and bad years with regard to the health of Koi, from imports from Japan and elsewhere. Last year certainly seemed to produce more than the average number of Koi health problems.

It is very important that we keep a realistic perspective of the facts and don’t get too carried away with some of the fantasy.

Firstly, despite all the hype, there has been only one proven case of a virus being introduced into this country in the last 18 months, and there is no proven source.

In previous years, there have been cases of SVC being reported, but the new virus appears to be related to the Herpes virus and has been wreaking havoc with koi stocks. (There is no evidence as yet that the virus emanated in Japan!)

Where did it come from?

It isn't known for certain where KHV originated, but it was positively identified in Israel in 1998. KHV has reportedly been confirmed in Northern Europe, the USA and South Africa, and has been associated with fish from Israel, Japan and the USA. (NB: All these cases could have been infected by other stock after import).

How does it work ?

KHV appears to be an immuno suppressant. It inhibits a Koi's ability to defend itself against other pathogens, particularly bacteria and parasites. Consequently, Koi suffering from KHV will often succumb to other infections. Reported symptoms range from the sudden death of healthy looking Koi, to more real symptoms such as bleeding from the gills, dry skin (where skin feels rough through the loss of mucus) and fin/body rot. However, these clinical signs are not necessarily an indication of a KHV infection.

What about quarantine ?

Due to the fact that it is a virus - KHV cannot be treated. Excellent husbandry and nutrition are likely to reduce the risk of your koi succumbing to KHV, but they will continue to be carriers if they have it and have survived.

What can you do ?

If you have any concerns that about the health of your koi, contact your dealer for advice. Due to the serious nature of this virus, ensure that you have clear and up to date records of where and when you purchased your koi. Obviously if you purchase from more than one dealer, and one of your stock start to show signs of infection, it could be that you could have contracted the virus from other resistant carrier koi in your pond that have not shown any clinical signs of the infection in the past.

What next ?

Keeping Koi is a responsibility for all of us. All of us must be pro active by being alert to the systems and methods for confirming KHV. Just be alert and aware and it will help all of us in the long run.

Please also bear in mind that koi stocks have been infected with viruses for years; carp pox is a good example , and whilst totally harmless to koi, is ironically related to the new Herpes virus identified recently.

As far as bacterial problems are concerned, there are, as always a number of reasons why bacterial problems occur or proliferate, and I think it is important to understand the factors which can lead to the problems which many of us have experienced at some time or other.

Article from MSB Koi Club Website at http://www.msbsection.co.uk/home.htm

More on KHV at KoiLab.com, article by Dr. E. Johnson DVM
http://www.koilab.com/articles/khv

More Information located at
http://www.koiherpesvirus.co.uk/index.html