It is extremely contagious, causes lethargy, erratic swimming movements, necrosis (death) of gill tissues, sunken eyes, haemorrhages, pale patches on the skin, increased mucus secretion, high mortalities (probably over 90%)... and affects Koi. Sounds familiar? Yes, of course.

However, unlike the world-famous carp disease known as Spring Viraemia of Carp (SVC), this latest disease appears to be caused by a herpes-like virus that only affects Koi and Common Carp (Cyprinus carpio), leaving goldfish and other carp-related species completely unaffected (Spring Viraemia affects these other species as well, in addition to Cyprinus carpio).

Since 1998, there have been several outbreaks of the disease among Koi and Common Carp in both Israel and the United States. More recently, though, it has also been reported as appearing in Koi imported into Europe from Japan. Outbreaks have been reported in the UK, Germany, Belgium, France and Holland. It is also suspected (but not proved) to be present in Malaysia. To my knowledge, no reports have, as yet, been received either from Spain, Portugal or Italy... or from some of the more northern European countries.., but it would not be surprising if the disease were to be present in these countries as well, but has not yet been scientifically documented. Despite these gaps in its presently known distribution, the virus (referred to as Koi Herpes Virus or KHV) is undoubtedly becoming widespread and causing great concern throughout the Koi industry and hobby.

The disease appears to be most virulent at temperatures between 17~23*C (although some people suggest the upper limit at which it can be detected to be 27*C). At other times, it seems to be, at least, relatively dormant. It is therefore a disease that can easily ‘hide away’ during the summer season, leading everyone, from exporters to retailers and consumers, to assume that their fish are healthy... only to be dramatically made aware that this is not the case once autumn arrives and temperatures begin to drop.

Countries where the disease is occurring are, obviously, studying it very closely, and not just to ascertain that the herpes virus is, indeed, the primary culprit and not a secondary ‘invader’. The UK’s Centre for Environment, Fisheries and Aquaculture Science (CEFAS), for example, has not categorically said that the herpes virus is the prime causative agent. It is, however, present in affected fish and is very likely to be, at least, an important contributing factor.

As things stand at the moment, KHV disease has not yet been officially declared by the Office Internationale des Epizooties (OlE) - the World Health Organisation for animals - as a ‘Notifiable Disease’ (i.e. one whose presence must - by law - be declared to the relevant authorities). This action can, however, be taken by individual countries without having to wait for the OlE to declare a disease as Notifiable. Should this happen, then the exporting countries which are identified as sources of KHV would be subjected to the same restrictions as those applied to Spring Viraemia of Carp, i.e. a two-year period of negative testing.

Worryingly, there are no treatments currently available for the disease. Apparently, the only effective measure that can be taken is destruction of all affected fish, followed by disinfection of the contaminated ponds, which - if carried out thoroughly - appears to be successful. However, keeping any survivors of an outbreak is probably likely in these fish becoming carriers of the disease, which, owing to its high infectivity rate, will contaminate all new stocks. Even if ponds are thoroughly disinfected, all newly imported fish should, of course, be subjected to a suitable period of quarantine. No doubt, we are going to hear a lot more about this disease over the coming months as we learn more about its sources, spread and, even, its very nature. For example, I held a meeting with some Israeli breeders in Barcelona (during SiZoo) and am now expecting official details about the disease, as well as some of the measures which have been taken in Israel that could well result in major advances in preventing further spread of the virus.