The signs of KHV often non-specific. You need to monitor your Koi Fish, if your Koi remains near the surface, swims lethargically, exhibits respiratory distress, has gill lesions, has gill mottling with red and white patches, bleeding gills, has sunken eyes, pale patches or blisters on the skin and uncoordinated swimming. The KHV seems to spread in the same ways as most herpes viruses: direct contact with infected fish, with fluids from infected fish, and/or with water or mud from infected systems. Once a fish has been exposed to the virus, it will always be a carrier. There is no known cure for Koi Herpes Virus. Mortality related to Koi Herpes Virus typically occurs between 18°C and 27°C. Almost no mortalities occur below 18°C, and there has been no reported occurrence of the disease above 30°C.
How do you know your Koi Fish has KHV? You need the assistance of a fish health specialist and a fish disease diagnostic laboratory. There are direct and indirect methods.
Direct methods include: virus isolation and identification (it means growing the virus or not) and PCR techniques (it means testing for the presence of KHV genes).
Indirect tests for KHV include ELISA testing, which looks for antibodies produced by the fish against the herpes virus These testing method can give proof that a fish was infected with KHV. This indirect test cannot determine if the fish is still infected with virus, so it is not recommended as a primary diagnostic tool.
As I mentioned there is no known treatment for KHV and the mortality is very high. If your Koi fish have been diagnosed with Koi Herpes Virus unfortunately, you have not got other choice than depopulation (it means eliminating the entire population). This approach should be followed by disinfection of all materials and systems that have contacted the infected fish.