Cyprinid herpesvirus-3 causes Koi herpesvirus, a viral illness in koi fish. It's a fatal and extremely contagious illness. All koi owners should be aware of the clinical indications of this disease, as well as the hazards of adding additional koi to their ponds without first testing them and quarantining them. One carrier fish is all it takes to wipe out a whole pond.
What is Koi Herpesvirus?
The koi herpesvirus (KHV) is a highly contagious virus that affects all types of koi and common carp ( Cyprinus carpio ). It's an OIE-reportable illness that can be found all over the world. Cyprinid herpesvirus-3, a virus related to carp pox (Cyprinid herpesvirus-1) (link to article) and goldfish hematological necrosis virus, causes the illness ( Cyprinid herpesvirus-2 ).
The koi herpesvirus is only active at particular temperatures, thus the fish may exhibit no indications of sickness in the winter when the water is colder. Once your pond water temperature reaches the active threshold for KHV, which is 60 to 77 degrees Fahrenheit, the most typical indicator of KHV is many fatalities (16 to 25C). Prior to death, fish may appear sluggish or have a diminished appetite, or they may show no clinical indications. Any pond with abrupt fatalities requires a thorough physical examination of all remaining fish as well as water quality tests. Other viral infections, such as Spring Viremia of Carp and Carp Edema Virus or Sleepy Koi Disease, have similar clinical symptoms.
Causes of Koi Herpesvirus
Physical contact with sick fish, transfer between fish on equipment such as nets, and water shared with infected fish are all ways for fish to develop Koi herpesvirus. This illness, which is classified as a herpesvirus, has a latent stage that lives in the brain tissue of fish. If a fish survives an infection, they are thought to be a carrier for the rest of their lives. Carriers can survive without showing clinical indications, but they propagate the virus to naive fish in the pond.
The spread of Koi herpesvirus is temperature dependant, like many other illnesses in fish. KHV replication is possible in ponds with temperatures ranging from 60 to 77F (16 to 25C). Clinical indications may appear in some ponds only when water temperatures are within a certain range, then fade when the temperature rises or falls.
KHV has been found to be carried by goldfish and other carp species. They won't display any symptoms of the sickness, but they can transfer it to other animals. Testing is available to see if other carp species have a carrier status.
Koi herpesvirus carriers are rarely chronic shedders. When they are stressed by poor water quality, overstocking, spawning, or other factors, they are more prone to release virus particles.
Your aquatic veterinary practitioner can test your Koi for Koi herpesvirus. Tissue or blood samples are taken from the fish, which must be sent to a diagnostic laboratory by a veterinarian. Active infections in fish expressing KHV antigens will be detected via PCR testing utilizing gill samples from living fish or internal tissues from recently deceased fish. ELISA testing, which uses a blood sample to screen for antibodies to KHV, can be used to identify any carriers.
The Koi herpesvirus has no treatment. However, elevating the water temperature in the pond or quarantine tank to 86 degrees F (30 degrees C) has been demonstrated to inactivate the viral infection and aid koi recovery. The koi's survival depends on good water quality, high oxygen saturation in the water, and treatment of secondary bacterial illnesses. If a fish survives infection, they are thought to be a lifelong carrier. KHV has a high death rate, ranging from 80 to 100%, so don't expect all of your fish to survive.
If an epidemic is confirmed, your veterinarian must report the incident to the state veterinarian. It is not necessary for you to depopulate your pond. Any survivors are up to you and your veterinarian to determine what to do with. If you decide to keep your fish, make sure the pond remains closed, with no new fish introduced and no fish removed.
How to Prevent Koi Herpesvirus
The easiest way to cope with Koi herpesvirus is to stay away from it. Proper quarantine and testing are the most crucial aspects of avoiding KHV. Temperature will influence quarantine length, since cooler water temperatures will impede the appearance of clinical symptoms, requiring a longer quarantine period. KHV takes 30 days to incubate at 50 degrees Fahrenheit (10 degrees Celsius), but just 3 days at 75 degrees Fahrenheit (23.8 C).
Some koi sellers may test fish before they depart, however the sort of testing will indicate whether or not the fish is a carrier. All testing must be done by a veterinarian, who will go through any possible positive results with you before you take your fish home.
Is it Contagious to Humans or Other Fish?
Humans and most other fish are immune to the koi herpesvirus. Infections have been seen in goldfish and hybrids of goldfish and common carp. These additional species can carry the illness without showing any symptoms, however testing is available to ensure they are not infected if they are to be mixed with koi.