Koi Herpes Virus (KHV) - Page 2
The role of biosecurity in KHV
Biosecurity encompasses not just the premises where Koi are farmed or sold, it also covers the precautions in place to prevent cross-infection between fish. Biosecurity protocols review and then require changes to the standards and practices of all those that come into contact in any way with Koi. It is a wide range of measures and procedures adapted to specific situations to minimise disease risks. The level of control in place to prevent the spread of health problems has to reflect every risk factor within the Koi Industry. To be effective it has to be applied at every stage of the process from the farm and throughout the distribution network. Nowadays it is safer to purchase Koi from a dealer who is certified as Biosecure or who can prove he has taken as many precautions as possible.
The need for 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 others. However, some diseases require specific incubatory criteria to be met before they materialise. Koi can be living together for many months or even years 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.
The best protection
Quarantine simply minimises risks. There are no foolproof measures against any disease and KHV is no exception. Any additional precautions taken during isolation must make each new Koi a little safer. Heating for most dealers and hobbyists is easy. Its application during isolation helps to trigger any potential health problems. The point being they happen during quarantine rather than in the pond to put other healthy Koi at risk. Tests are costly and limited to specific diseases such as KHV so do not reduce other 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.
By outlining heat-ramping during quarantine we must make clear it is not a scientifically supportable procedure. Koi that do not develop KHV during the ramping can still carry the virus. What has been found is that Koi that have been through several heat ramping sessions are statistically less likely to prove to be carriers 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 fish 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.
How long should quarantine take?
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 and one month not sufficient. 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 difficult quarantine the move to the main pond must minimise the stress associated with any change of environment.
Vaccination in Koi
The disease we commonly term carp pox, which causes the unsightly shiny white tumours in colder weather, is scientifically termed Cyprinid Herpesvirus (CHV). It is a relatively harmless affliction also caused by a herpes virus, as they are 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 implications with human health a major concern. Most fish production is destined for human consumption, whilst Koi are ornamental fish they are eaten in many countries including Japan. Vaccinated fish are not allowed in the human food chain but enforcing this means the legislators require yet another test to detect vaccinated Koi so a vaccination programme is not always a quick solution that covers everyone’s interests in fish.
Vaccine production requires highly skilled research and the application of a lot of technology. A vaccine must satisfy international legislation and is costly to manufacture and then market, so sales must be possible yet the Koi sector is small. Certain types of vaccine can actually perpetuate the disease they are targeted to prevent. Attempts at vaccines have already 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. Since the advent of DNA vaccines, we can be more positive about controlling disease like KHV via immunisation.
The PKDA Consultant has experience with KHV research and vaccine trials and it is her view that issues still remain in respect of the vaccination of Koi. She reports that based on her own investigations the KV3 vaccine is far safer than any previous vaccine used in Koi production in Israel. However, she states that from the scientific perspective experience suggests that remote as it may be, a very small risk remains due to the fact the vaccine in use is of a type that can revert to wild type KHV. She suggests that whilst she has personally had no cases in her facilities, dealers and hobbyists should not mix vaccinated Koi with those naive to KHV unless they are prepared to take this small risk. Buying koi with an unknown history from a hobbyist or from an unquarantined source also poses a risk. Vaccination will become even more confusing when vaccines based on different principles are in use so this will always be a confusing area for hobbyists. The major role for vaccinated Koi at this current time is in a pond that stocks them exclusively and in ponds in which the Koi are survivors of KHV and cannot live with those naive to the disease.
Enjoy Koi –Keeping
January 2012: In the last two years, the PKDA Consultant has seen fewer cases of KHV. In liaison with dealers, pond side service and pond maintenance operatives as well as Cefas, the consensus is that there has been a steady decline in outbreaks of KHV and cases undiagnosed although suspected of being KHV. There are numerous reasons for this decrease but it is a very positive factor. However, this does not means the disease has gone away; a virus is a very clever pathogen. Our Consultant advises everyone to continue take every possible precaution. Nothing is ever as straightforward as Koi enthusiasts would like in respect of Koi health, as this is a very complex scientific field. Hobbyists can be assured that keeping Koi remains an enjoyable hobby when quarantine is seen as yet another aspect of the hobby and not as an obstacle. Only then can the risk of all disease be seen in its true perspective.
