Koi herpesvirus disease in carp

Abstract

A disease in the koi carp (Cyprinus carpio koi) and the common carp (Cyprinus carpio carpio), caused by the herpesvirus and accompanied by a high mortality rate, has spread across numerous fish ponds all over the world since 1998, resulting in massive mortality and significant financial losses. The herpesvirus-like virus, called the koi herpesvirus (KHV) has been isolated and identified from the koi and the common carp in the course of the incidences of massive mortalities. The first appearance of a disease with a high mortality in the common and the koi carp caused by the koi herpesvirus (KHV) was described in 1998 in Israel and the United States of America (USA). Since that time, a large number of cases of outbreaks of this disease have been confirmed throughout the world, including the USA, Israel, and a large number of European countries. The deaths occurred seasonally, in late spring or early autumn, when the water temperature was from 18-28ºC. The most important factor of the environment that affects the occurrence and gravity of this disease is the water temperature. This disease is currently considered one of the factors that present the biggest threat to populations of the common and the koi carp. Diseased fish are disoriented, their movements uncoordinated, their breathing rapid, gills swollen, and they have local skin lesions. The virus was isolated from tissue of diseased fish and cultivated on a KF-1 (koi fin cells) cell line. Electronic microscopy examinations revealed virus identical viral particles of the Herpesviridae family. Analyses of the virion polypeptide and DNA established differences between the KHV and the previously known herpesvirus of the Cyprinida family, Herpesvirus cyprini (CHV), and the virus of the channel catfish (Channel catfish virus - CCV). In the years 2004 and 2005, high mortality was established among one-year and two-year carp fry on three fish ponds. At two ponds, the deaths occurred among one year and two-year carp fry during the spring period, when the water temperature was over 18ºC. During the autumn period, mortality was recorded among one-year carp fry at water temperatures above 23ºC. On the grounds of the determined pathomorphological changes and the high mortality during the period of the year when the temperature was above 18ºC, we suspect that KHV is also present in fish ponds in Serbia, even though the virus itself has not been isolated. The objective of this work is briefly to present the relevant data on this disease which is inflicting significant losses to carp production, to show the current distribution of this disease, the diagnostic methods, and the possibilities for the prevention and control of KHV