Koi herpes virus ( or CyHV-3) is a viral disease that is very contagious to the common carp Cyrpinus carpio. It is most common found in ornamental koi, which are often used in outdoor ponds or as feeder stock. It can cause 80-100% mortality among infected groups. The first case of KHV was reported in 1998, but not confirmed until later in 1999.
The virus transfers between fish extremely rapidly especially at temperatures between 15-27 degrees C. Studies from the Hebrew University, Israel have concluded that contact with10-40 virus particles per ml of water for five minutes, is sufficient to result in a 70% mortality rate within 15 days.
KHV is a DNA-based virus. After discovery, it was identified that KHV is indeed a strain of herpesvirus. Like other strains, KHV stays with the infected fish for the duration of their life, making the recovered and exposed fish potential carriers of the virus. Koi fish infected with KHV may die within the first 24-48 hours of exposure.
Transmission of the Disease
Direct contact with other infected fish
Contact with fluids and material from infected filtration/pump systems
Contact with fluids from infected fish
Fish Affected by KHV
Ornamental Koi
Common Carp (Cyprinus carpio)
Common Goldfish (Carrassius auratus) and Rucian Carp (Carrassius carassius) can be infected with the disease and become carriers but seem to be immune to it themselves. Grass Carp (Ctenopharynodon idellus) and Tench (Tinca tinca) may also become carriers.
Symptoms of KHV include:
* Gill mottling
* Red and white patches appearing on gills
* Bleeding gills
* Sunken eyes
* Pale patches
* Blisters
Diagnosing KHV
Due to the fact that there may be no outward signs of KHV it is often difficult to diagnose. Fish may carry the virus for some time and only post mortem examination will reveal damage to the gills. Also some symptoms are similar to those of other carp diseases and misdiagnosis and treatment can occur.
Cefas Tecnology Limited (CTL), a subsidary of Cefas (Center for Environment, Fisheries & Aquaculture Science) have developed three types of test for the detection of the virus. Further information of these tests is available on their site Here
Treatment
Currently there is no treatment for KHV. Antiviral drugs are not available to treat KHV or any other viral diseases of cultured fish.
Studies have shown that koi may survive an outbreak of KHV if water temperatures are increased to 86°F (30°C) during the outbreak (Ronen et al. 2003, Hebrew University, Israel). Unfortunately using this technique only slightly increases survival rates, and in addition, artificially raising water temperatures above 80°F in holding facilities may lead to increased cases of other more common bacterial and parasitic diseases.
High water temperatures are not usually recommended for routine husbandry and management of koi and common carp. In addition, and more importantly, koi which do survive a KHV outbreak or those exposed at high water temperatures will become carriers of the virus. This means that they can pass on the virus to susceptible fish when conditions are appropriate for viral shedding and infection. These carrier fish will not succumb to KHV disease or show signs of clinical infection.
Vaccination
Currently there is no approved vaccine in the for KHV. Also research has shown that during experimental vaccine studies fish did develop antibodies, became immune to the disease and survived an infection. However, there is still the potentail for these fish to become carriers of the virus and infect other fish with which they come into contact.
Prevention
To date, quarantine is the most dependable method of avoiding introducing the virus into an established pond.
To be effective all new fish should be kept in a seperate system, in a different building or area from the established fish. Established fish should be fed, handled and maintained before new fish to prevent cross-contamination. Likewise any equipment used should be kept completely seperate and be used only for established or new fish.
Foot baths and hand washes should be used by anyone entering or leaving the area.
Fish should be quarantined for a minimum of 30 days. Specifically for KHV, new koi should be quarantined in water that is 75°F (24°C) for at least 30 days. At the end of the quarantine period, any sick fish should be examined by a veterinarian and/or diagnostic lab to rule out KHV or other diseases. If all fish appear healthy, blood samples should be collected from these quarantined fish and submitted for antibody detection using either ELISA or VN methods.
Please Note There is an order in place, The Diseases of Fish (England and Wales) Order 2007 (SI 2007 No. 864), which came into effect on 6th April 2007. It states that is is a legal obligation for anyone involved with rearing or keeping fish (ie. fish farmers and their staff, anyone who sells and/or keeps fish) to inform the Fish Health Inspectorate if they suspect that any of their fish may be infected with this virus. Full Details Here
