Koi Herpesvirus
What is it?
Koi herpesvirus disease (KHVD) is a very infectious herpesvirus infection capable of inducing a contagious and acute viraemia
in common carp (Cyprinus carpio) and varieties such as koi carp and ghost carp.
Since 1998, there have been
cases in the UK, Europe, US, Indonesia, Israel
and Japan.
Where and When Might it Occur?
Outbreaks of disease
generally occur at water temperatures between
1625C.
The virus only appears to infect
Cyprinus carpio which includes koi, ghost koi
and common carp.
Goldfish and other
cyprinids are not known to be affected by or
carry the virus.
Water is the major abiotic vector. However, animate vectors (e.g. other fish species, parasitic
invertebrates and piscivorous birds and mammals) and fomites may also be involved in transmission.
Diagnosis
During a KHVD outbreak there will be a noticeable increase in mortality in the population. All age groups
of fish appear to be susceptible to KHVD, although, under experimental infection, younger fish up to
one year old are more susceptible to the disease.
On closer examination of individual fish, typical clinical
signs include pale discolouration or reddening of the skin, which may also have a rough texture, focal or
total loss of epidermis, over- or under-production of mucus on the skin and gills, and pale discolouration of
the gills.
Other gross signs include enophthalmia (sunken eyes) and haemorrhages on the skin and base
of the fins, and fin erosion.
Fish may also become lethargic, separate from the shoal and gather at the water inlet or sides of a pond and gasp
at the surface of the water. Some fish may experience loss of equilibrium and disorientation but they may
also show signs of hyperactivity
Morbidity of affected populations can be 100 per cent, and mortality 7080 per cent, but the latter can be as high
as 90 or 100 per cent.
Secondary and concomitant bacterial and/or parasitic infections are commonly
seen in diseased carp and may affect the mortality rate and display of signs.
Control/Treatment
There is currently no treatment
available for this disease.
Methods to control and prevent KHVD should mainly rely on avoiding exposure to the virus coupled with good
hygiene and biosecurity practices.
This is feasible on small farms supplied by spring or borehole water and a
secure system to prevent fish entering the farm via the discharge water.
SOURCE: Defra and OIE