Major KHV outbreaks hit UK fisheries

Three stillwater fisheries in the south and south east of England have been hit by the UK's most serious outbreak of KHV ever.

The Centre for Environment, Fisheries and Aquaculture Science (Cefas) and the Environment Agency are investigating three outbreaks of Koi Herpes Virus at the three fisheries and have placed fish movement restrictions on the waters.

Cefas reports that the outbreak represents the first KHV mortalities reported this year and that it has been the most serious in terms of losses since the disease was first recorded in the UK.

The Environment Agency and Cefas are trying to determine the source of the outbreaks and identify whether any other waters have been infected by the deadly virus.

KHV, now formally known as Cyprinid Herpes Virus 3 or CyHV-3, is a member of the Herpesviridae family and has been responsible for mass mortalities in carp around the world, with Israel, Japan and South Africa particularly hard hit.

The disease occurs at temperatures between 15 and 28C and results in mortality rates between 50 and 95%. It was first officially reported in the UK in 2000.

The virus can remain latent in infected carriers for long periods and only becomes symptomatic when the temperature rises to 15-28C. As a result, dealers are advised to isolate newly imported carp and heat-treat them for several weeks in order to trigger the symptoms.

KHV is not yet a notifiable disease in the UK and Cefas now charges a fee to determine whether fish are infected with the virus. This may have led to a drop in the number of cases that get officially reported.