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Koi Herpes Virus

Georgia Department of Agriculture would like to remind Georgia koi and common carp producers/importers to be vigilant in protecting their livestock and pets from the introduction or exposure to Koi Herpes Virus (KHV). KHV is a highly contagious viral pathogen affecting common carp (Cyprinus carpio), including koi carp. 

 KHV is known to occur in the U.S. both in wild and farm-raised susceptible species but may still cause high mortality and morbidity in naïve (unexposed) susceptible populations. Producers and importers should know the health and vaccination status of the animals they are raising or importing, respectively. To know the health status, producers and importers are encouraged to ask for health testing documentation specific for KHV from their animal suppliers. 

 KHV is a significant disease of koi carp and common carp caused by cyprinid herpesvirus 3 (CyHV-3). It has caused mass die-offs of both common carp and koi. Mortality rates of 80%-100% are typical for affected koi ponds. Goldfish and grass carp do not exhibit signs of disease but can act as carriers of the virus and contribute to the spread of the disease to naïve populations of koi and grass carp. Due to its continued spread in Asia and Europe, and its endemic status in the United States, confirmed cases must be reported to the USDA-APHIS Assistant Director. The disease is not reportable in the state of Georgia.

 KHV is transmitted in water, feces, contaminated equipment, and by direct contact. Temperature is the most important factor determining disease development. Outbreaks are most severe at 64⁰ F - 82⁰ F with epidemics typically occurring in spring or summer. The disease does not develop <55⁰ F or >86⁰ F. The permissive temperature range is generally considered to be 73⁰ F to 82⁰ F. Koi which survive clinical disease often become carriers. Carriers that are held in cool water (<68⁰ F) can harbor the virus for lengthy periods and shed the virus once the water temperature is in the low seventies. 

 Several diagnostic tests can be used when clinical signs of KHV are observed. PCR or virus isolation and identification can be used to confirm the infection in dead fish.  Blood, gill tissue, feces, or mucus samples may be used to assess the status of very ill fish. However, using these samples to test clinical normal fish can result in a misdiagnosis and are not appropriate screening methods for carrier fish. 

 If the infection is confirmed in a population of koi carp, depopulation is strongly recommended. Prevention of KHV infection is best accomplished with careful quarantine protocols. A minimum quarantine of 30 days at 75⁰ F is recommended to minimize the chance of introducing KHV to an established koi population. After the initial quarantine period and additional testing, if necessary, a fish known to be free of KHV may be placed in the established group. This fish can increase the likelihood of detecting the virus by demonstrating clinical signs of disease because asymptomatic carriers in the test group may only shed virus and not display clinical signs at the permissive temperature.

References   Aiello, Susan and Micheal  A. Moses. 2016. The Merck Veterinary Manual. Whitehouse Station, N.J. : Merck + Co., in cooperation with Merial LTd.   Noga J., Edward. 2010. Fish Disease Diagnosis and Treatment. 2nd Ed. Wiley- Blackwell.   Saint-Erne, Nicholas. 2010. Advanced Koi Care for Veterinarians and Professional Koi Keepers. Erne Enterprises.

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