Koi Pox; herpes virus.
Koi herpes virus (KHV), a viral disease highly contagious to fish, may cause significant morbidity (sickness or disease) and mortality in common carp (Cyprinus carpio) (Hedrick et al., 2000; OATA, 2001). This species is raised as a food fish in many countries and has been selectively bred for the ornamental fish industry, where it is known as koi. Historically, the first outbreak of KHV was reported in 1998 and confirmed in 1999 in Israel.
Since then, other cases have been confirmed in the United States, Europe and Asia (Hedrick et al., 2000; OATA, 2001; Anonymous, 2003). This information sheet is intended to inform veterinarians, biologists, culturists, and hobbyists about KHV.
What Is KHV?
KHV is currently classified as a DNA-virus belonging to the virus family Herpesviridae (i.e., a herpes virus). Although there has been some scientific discussion regarding the accuracy of this classification (Ronen et al., 2003), more recent work (Waltzek et al., 2004) shows strong evidence that KHV is indeed a herpesvirus, based on morphology and genetics. KHV disease has been diagnosed in koi and food fish carp (Hedrick et al., 2000; OATA, 2001). Other related cyprinid species such as the common goldfish (Carassius auratus) and grass carp (Ctenopharyngodon idella) seem to be unaffected by KHV. As with other herpes viral infections, KHV is believed to remain in the infected fish for life, thus exposed or recovered fish should be considered as potential carriers of the virus (OATA, 2001).
KHV disease may cause 80-100% mortality in affected populations, and fish seem most susceptible at water temperatures of 72-81°F (22-27°C) (OATA, 2001). This viral disease affects fish of various ages, but cohabitation studies show that fry have a greater susceptibility than mature fish (Perelberg et al., 2003).
What Are the Signs of KHV?
Clinical signs of KHV are often non-specific. Onset of mortality may occur very rapidly in affected populations, with deaths starting within 24-48 hours after the onset of clinical signs. In experimental studies, 82% of fish exposed to the virus at a water temperature of 22°C died within 15 days (Ronen et al., 2003). KHV infection may produce severe gill lesions and high mortality rates. In some cases, secondary bacterial and parasitic infections may be the most obvious problem, masking the damage caused by the primary viral infection. Behaviorally, affected fish often remain near the surface, swim lethargically, and may exhibit respiratory distress and uncoordinated swimming.
External signs of KHV may include gill mottling with red and white patches (see picture) (similar to Columnaris disease), bleeding gills, sunken eyes, pale patches or blisters on the skin. Microscopic examination of gill biopsies often reveals high numbers of bacteria and various parasites (Hedrick et al., 2000; OATA, 2001; Goodwin, 2003).
Internal signs of KHV are inconsistent and non-specific, but they may include adhesions in the body cavity and a mottled appearance of internal organs (Hedrick et al., 2000; Goodwin, 2003).
How Do Fish Get Infected with KHV?
The herpes virus that is responsible for KHV seems to spread in the same ways as most herpes viruses. Methods of transmission include direct contact with infected fish, with fluids from infected fish, and/or with water or mud from infected systems. Depending upon water temperature, fish that are exposed and susceptible may become infected and either develop the disease and die or become carriers of the virus (OATA, 2001). Goldfish and other fish in the carp family are not susceptible to KHV disease, and they do not appear to act as carriers of the virus (Perelberg et al., 2003; Ronen et al., 2003).
Level One UV Sterilization is very effective against this virus and although not a treatment for infected fish, a properly installed/quality UV Sterilizer should be employed for prevention.
If your pond (or aquarium) already has a UV Sterilizer, it is also imperative to change your UV Bulbs every six months for level one UV Sterilization maximum effectiveness.
OTHER RELATED/SUGGESTED READING FOR AQUARIUM OR POND KEEPING:
*Pond Care Information
An easy to follow article about pond care with many more in depth resources as well as product resources cited
*Aquarium Lighting Information
An in depth article that I recommend and have found to be the most up to date anywhere. It includes information about the many types of lights including LED Aquarium Lights.
Probably the best article on the subject of aquarium chemistry I have found. The author gets it right with the science behind electrolytes, GH, KH and more
Copyright 2019, By Steve Allen