Koi herpes virus (KHV), a viral disease highly contagious to fish, may cause significant sickness or disease and mortality in koi carp (Cyprinus carpio). Historically, the first outbreak of KHV was reported in 1998 and confirmed in 1999 in Israel. Since then, other cases have been confirmed in the United States, Europe and Asia. This information sheet is intended to inform hobbyists about KHV.

What Is KHV?
Recent work shows strong evidence that KHV is indeed a herpesvirus, based on morphology and genetics. KHV disease has been diagnosed in koi and foodfish carp. Other related cyprinid species such as the common goldfish and grass carp seem to be unaffected by KHV. As with other herpes viral infections, KHV is believed to remain in the infected fish for life, thus exposed or recovered fish should be considered as potential carriers of the virus.
KHV disease may cause 80-100% mortality in affected populations, and fish seem most susceptible at water temperatures of 72-81°F (22-27°C) (OATA, 2001). This viral disease affects fish of various ages, but cohabitation studies show that fry have a greater susceptibility than mature fish.

What Are the Signs of KHV?
Clinical signs of KHV are often non-specific as it attacks the immune system of the fish. Onset of mortality may occur very rapidly in affected populations, with deaths starting within 24-48 hours after the onset of clinical signs. In experimental studies, 82% of fish exposed to the virus at a water temperature of 22°C died within 15 days. KHV infection may produce severe gill lesions and high mortality rates. In some cases, secondary bacterial and parasitic infections may be the most obvious problem, masking the damage caused by the primary viral infection. Behaviorally, affected fish often remain near the surface, swim lethargically, and may exhibit respiratory distress and uncoordinated swimming.
External signs of KHV may include gill mottling with red and white patches, bleeding gills, sunken eyes, pale patches or blisters on the skin. Microscopic examination of gill biopsies often reveals high numbers of bacteria and various parasites.

How Do Fish Get Infected with KHV?
The herpes virus that is responsible for KHV seems to spread in the same ways as most herpes viruses. Methods of transmission include direct contact with infected fish, with fluids from infected fish, and/or with water or mud from infected systems. Depending upon water temperature, fish that are exposed and susceptible may become infected and either develop the disease and die or become carriers of the virus. Goldfish and other fish in the carp family are not susceptible to KHV disease, and they do not appear to act as carriers of the virus.

How Does Water Temperature Affect KHV Disease
The virus appears to have an incubation period of 14 days following the introduction of infected fish to naïve fish (fish that have not been exposed before). However, incubation may be longer, indicating that appropriate temperature and possibly a second trigger may be necessary for outbreaks to occur. Mortality related to KHV disease typically occurs between 64°F and 81°F (18-27°C). Almost no mortalities occur below 64°F, and there has been no reported occurrence of the disease at or above 86°F.

Is there a cure for KHV?

No cure is available for KHV at the current time.

Quarantine is the most dependable method to avoid introducing KHV to a naïve population. To apply a quarantine effectively, all new fish must be kept in a separate tank or system, and ideally in a different building or area from the resident fish. Resident fish should be fed, handled, and maintained before the new fish. The quarantined fish require equipment such as nets, buckets, and siphon hoses that are used only for them. In addition, disinfectant foot baths and hand washes should be used by any personnel on entering and leaving the quarantine area. Fish should be quarantined for a minimum of 30 days.The best way to prevent KHV is to know your fish suppliers and have a good working relationship with them.

Break through in prevention of KHV and SVC

Virkon S is not a cure but will help stop bacterial disease and viruses spreading.

Following the recent serious koi herpes virus outbreak in most of the key Koi countries, including Japan, Israel and Germany, as well as the UK, it became clear that the Koi fraternity could not depend on out dated remedies and would have to look to the modern techniques of biosecurity practised in other livestock areas. This is when the keynote role that Virkon S plays so successfully in pig, poultry and cattle production worldwide became clear. The fact that the original Virkon S, the most proven and effective virucide for animals, has now been tailored specifically to Virkon S Aquatic for the biosecurity requirements of the Koi owner, where lower fish toxicity and environmental and user safety are paramount, this anti_virus and anti_bactera product in tablet form, is a great step forward for KHV and SVC infection control and disease management in this rapidly expanding hobby".

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