KHV, Covid 19 for Koi

With the recent outbreak of the devastating Coronavirus, our world has suffered terrible losses, both in terms of human life and throughout the economy. Nothing is more precious than human life, and in no way, can we compare the devastating effects of the Coronavirus disease to the losses, in any form, suffered by koi fish. Our only intention is to explain just how quickly and deadly viruses can change our lives in any realm.

The Origin of KHV

In 1996, the koi world experienced an outbreak of a totally new virus called the “Koi Herpes Virus” (Cyprinid herpesvirus 3) commonly referred to as “KHV". Most experts agree that the virus was first detected in Israel and then subsequently transferred to ponds in the United Kingdom. From that time on, cases have been confirmed in almost every country (with the exception of Australia). The KHV outbreak brought devastating losses of life to both the koi hobbyist and to the retail koi industry. A staggering mortality rate of 80% and above in a pond is not uncommon.  In this blog, we will explore its origin, the efforts to contain it, and the possible cures offered by the many veterinarians and biologists who have dedicated countless hours to finding a cure.

What is KHV?

Koi Herpes Virus is a DNA virus that causes a highly contagious disease found exclusively in ornamental koi and in common carp. Although KHV has never been associated with disease in any other species and cannot be transmitted to humans, tests on goldfish have shown them to be asymptomatic carriers (contagious, but with no symptoms).  As mentioned above, the disease was detected in Israel in 1996 and quickly spread to the United Kingdom and then throughout other parts of Europe and Asia. The disease found its way to America in 2009 in the state of Minnesota. Believed to be contracted by a contagious fish in a koi show, the KHV virus quickly spread throughout the US koi retail market and to koi hobbyists.

What does KHV look like?

The symptoms of the KHV infection include red and white mottling of the gills, gill hemorrhaging, sunken eyes, and pale blisters on the skin. Internally, the kidney, gill, spleen, intestine, and the brain are damaged. Because the gills are severely affected, it inhibits breathing and causes the fish to suffocate and die. Behaviorally, infected fish often “grope at the surface for air” or swim on their sides and act lethargic. They will bump into the sides of the walls or other objects.  This nasty disease works very quickly. Studies show that the fish will begin to die within 24 to 48 hours of the initial onset of these signs. Outbreaks typically occur in spring and autumn when water temperatures are between 60°-77°F with an incubation period of 7-21 days.  EVEN IF SOME KOI SURVIVE THE INITIAL ONSLAUGHT OF THE DISEASE, THEY MAY STILL REMAIN ASYMPTOMATIC. IT IS MOST IMPORTANT TO EITHER DE-POPULATE THEM (ELIMINATE THE ENTIRE POPULATION) OR KEEP THEM SEPARATE FROM ANY NON-INFECTED FISH. DO NOT TRANSFER ANY KOI OR WATER FROM ONE INFECTED POND TO ANOTHER. DISINFECT WITH LIQUID CHLORINE ALL NETS AND OTHER EQUIPMENT ASSOCIATED WITH ANY HANDLING OF THE INFECTED KOI.

White Mottling on the Gills (in Red)	Pale Blisters (Spots) on the Skin

Is there any cure for KHV?

In 2003 an Israeli research group developed a live vaccine for KHV. However, with what looked to be a promising cure, concerns were raised regarding the efficacy of the vaccine and the length of protection to the vaccinated fish. Also, it is unknown if vaccinated fish become carriers. So, the vaccine was not found to be financially viable and therefore was not mass-produced.

There is, however, a much simpler solution to stop the fish from dying. According to Dr. Eric Johnson a DVM (veterinarian) of Georgia, KHV is a temperature-sensitive virus. Meaning that it is latent (hidden) in temperatures below 68°F.  It manifests and is most aggressive in water temperatures between 68°-78°F. BUT, when the water temperatures are raised slowly to above 80°, the virus clears. The infected fish should be kept in this heated water (86°F) for 2 days. It is not entirely known whether the treated fish will become asymptomatic, so they should not be placed in any pond with healthy fish. One of the side effects with this approach is that the red color on certain koi, like Kohaku and Sanke might fade out. But, for those hobbyists who have grown very fond of their koi and want to save them, this offers a viable solution. 

Preventing the Spread of KHV

As with the Covid-19 virus, preventing the spread of KHV is critical to koi hobbyists. As an example, during koi shows, contestants and handlers are encouraged to use the English style method of displaying their koi which keeps different owners separated when showing and judging. In addition, using separate nets, siphon hoses, and other equipment must be used for each tank. This method is in direct contrast to Japanese shows which koi from different owners are placed together in the same tank. This method could very easily result in the spread of the disease. When purchasing new fish, koi hobbyists should ask the store where they purchase their koi and whether their fish are both tested and quarantined before being placed on display to sell. If tested, the store should be able to provide the results upon request.

Following the above precautions will help minimize the spread of KHV and bring a little more peace of mind to all koi enthusiasts concerned with this disease.