UK's biggest ever KHV outbreak gets worse

The Environment Agency has placed voluntary fish movement precautions on six still water fisheries in the midlands, south and east of England after confirming that massive fish losses there were due to the deadly Koi Herpes Virus.

The owners of the fisheries reported significant fish losses over the past week and tests have confirmed that the mass mortalities seen were due to KHV. In order to prevent the further spread of the virus, the Environment Agency has instructed the owners to cease all fish movements.

Last month, three still water fisheries in the south and south east of England were also struck by the virus.

Five other fisheries are also suffering fish losses that appear to have symptoms consistent with KHV. Samples of the fish have been taken away for laboratory analysis, with the results expected later this week.

The nine reported cases in the past month mean that the current outbreak of the fish virus is by far the biggest the UK has ever seen.

Voluntary movement restrictions

The Environment Agency fish movements advisor, Paul Lidgett said: "At this stage the Environment Agency will not be releasing the name of any fishery being tested for KHV, as the last thing we want to do is deter fishery owners from coming forward if they suspect an outbreak in their waters.

"We recognise that anglers may be concerned about spreading the disease inadvertently. However, the likelihood of KHV being transferred between fisheries by anglers' nets is negligible when compared to the threat via fish transfer, so stopping all fish movements at the infected sites is the best way of prevening the virus spreading further."

The Environment Agency does not have the powers to close down fisheries infected by the virus, they have advised all infected premises to cease angling and add their own biosecurity measures to ensure that the disease is contained.

KHV outbreaks typically occur in the hottest weather, when the water temperature is between 18 and 28C as the virus is asymptomatic at lower temperatures.

A number of cases are officially reported each year, but many more are believed to go unreported, because the disease is not yet notifiable and businesses to not have to legally declare an infection. Just 16 cases have been reported in UK fisheries since 2002, but nine of those have been recorded in the past three weeks.

The Environment Agency says it is working with the infected premises to help them recover from the impact of the disease, which can kill up to 80% of fish and leaves others as potentially dangerous carriers. It is offering advice on restocking and disinfection and believes that with the right approach the waters can recover.

Lidgett added: "Koi Herpes Virus is not currently a notifiable disease under the EU Fish Health regime. This means that there is no legal duty to report infections to the Department of Environment, Food and Rural Affairs (Defra) and the Centre for Environment, Fisheries and Agriculture Science (Cefas), on Defra's behalf, have no powers to impose movements orders themselves. Any controls are based entirely on Section 30 administered by the Environment Agency.

"However, a new EU Fish Health Directive expected in September this year should change this, making KHV a notifiable disease. We welcome this as it would give Cefas powers to investigate KHV mortalities and trace the source of the outbreak. It would also place a legal duty on fishery owners to report suspected KHV mortalities on their sites."

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 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.