Since May 1998 outbreaks of what has become known as CyHHV-3 or in its popular names Koi Herpes virus (KHV) or CNGV (Carp Necrosis Gills Virus) caused mass mortalities in private stocks and fish farms all over the world. The disease results an enormous financial losses for those enterprises concerned.

When the virus infects a group of fish, one could expect to lose upwards of 90% of the group. There is no cure for the viral infection

The disease is pathogenic to the Koi and Common Carps fish through the water. Both fish are of the Cyprinus carpio species.

It reaches high mortality within 6-21 days from the start of the infection.

The disease is temperature related. It appears and causes mortality at a limited temperature range between 180C – 280C.

KHV infection may produce severe gill lesions and high mortality rates. In some cases, secondary bacterial and parasitic infections may be the most obvious problems, 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 (Figure 1), 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. The internal signs include superficial bleeding signs of the skin and increased mucus secretion in the water.