KHV: Treatment and Prevention

There is no known cure for KHV however, with supportive care in combination with raising the water temperature above 30oC, it may be possible to save some of the fish from succumbing to the disease. This is usually reserved for pet fish that have special significance to their owners. This is because fish  who survive KHV infection remain persistently infected and are capable of intermittent shedding of the virus which can then infect naive fish. Thus the options for koi hobbiests include either sacrificing ALL fish, thoroughly disinfecting, and starting over or keeping their fish as a closed “KHV positive” collection. The options for fish farms that contract KHV include the emergency harvest of fish still fit for human consumption, and the rapid depopulation of all clinically affected fish followed by thorough disinfection. Chemicals shown to be effective in the disinfection of KHV include ethyl alcohol, iodophor, benzalkonium, and sodium hypoclorite. KHV is also killed by exposure to UV radiation and temperatures over 50oC for 1 minute.

Since treatment of KHV is limited, prevention becomes very important. KHV is mainly spread by direct contact between fish however, it can also survive in water for up to 4 hours and thus can also be spread via fomites such as nets, pails, and other pond equipment contaminated with infected water or via transport hosts such as humans, birds, etc. Thus the best way to prevent KHV is to quarantine all new fish and prevent cross contamination of ponds and aquariums until it is known that the new fish are not infected with the virus (KHV testing or quarantine for 4 weeks to 2 months at 24oC). In some aquaculture facilities KHV is prevented by strict biosecurity procedures including quarantine procedures for new fish, the use of sentinel fish to detect the presense of carriers, restriction of movement of fish and water between farms and the environment, and frequent disinfection of equipment, ponds and fish eggs.

There are no vaccines for KHV currently available in Canada or the United States. A live attenuated vaccine has been used in Israel for the prevention of KHV since 2004 and the manufacturer of this vaccine (KoVax) is currently in the process of getting the vaccine licensed in the USA. Kovax reports efficacy results for its vaccine (KV3) of 90-95% vitality of vaccinated fish versus 70-100% mortality among unvaccinated fish. There are also various institutions and companies around the world attempting to develop their own KHV vaccine including the Canadian company Novartis who received funding (1.8 million dollars over 5 years) from the Canadian government in 2006 to develop a vaccine. As well, Japanese scientists are trying to develop a liposome based oral vaccine containing inactivated KHV and have had some initial success in laboratory studies. Other scientists are attempting to breed a genetically KHV resistant breed of carp.