How is koi herpesvirus disease (KHVD) expressed?

Clinically, we can observe hypersecretion of mucus, skin and gill ulcers, congestion of the skin and fins, lethargy with possible phases of hyperactivity, enophthalmos (eyes retracted into their orbits)…

The expression of the disease varies depending on the temperature, the population and the breeding conditions. It is expressed between 16 and 26°C but never below 13°C and above 30°C. High temperature inhibits viral multiplication and below it is too slow or inactive. Fish infected below 13°C can act as a reservoir for the disease (healthy carriers).

Fish surviving an episode of KHVD can also redevelop the disease during a drop in immunity and stress (transport, handling, etc.) between 16°C and 26°C.