KHV: What is it?

Koi herpes virus (KHV) or more specifically cyprinid herpes virus 3 (CyHV-3) is a viral disease of the species Cyprinus carpio which includes the wild common carp, mirror carp and ghost carp as well as the domestic koi carp and goldfish hybrids of these varieties.

KHV is a double stranded DNA virus belonging to the family Herpesviridae and is one of 3 cyprinid herpeviruses. The others of which include carp pox virus (CyHV-1) and goldfish haematopoietic necrosis virus (CyHV-2).  KHV can affect carp of all ages but it seems as if adult carp have a higher risk of being infected. KHV causes severe disease and has a high mortality rate. Please see the section on Signs and Symptoms for more details on the clinical signs of KHV. As well, like other herpes viruses, fish who survive the disease remain persistently infected. The virus has the ability to become latent and then periodically reactivate potentially infecting new hosts when it does. The virus is shed directly into the water from the gills and skin and possibly also the urine and feces. Treatment for KHV is limited and the focus should be on preventing KHV. There is currently no vaccine licenced for use in either Canada or the USA. As far as we know KHV posses no zoonotic risk.

As of July 2009 there have been positive identifications of KHV in 30 countries and the disease is continuing to spread. Canada is among the countries that have tested positive for KHV among wild carp populations. The United States has had positive KHV identifications among both wild carp as well as in contained systems. For a complete list of countries that have had confirmed KHV infections please refer to: Results of Global Koi Herpes Virus Questionnaire 2009.

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