Current knowledge on koi herpesvirus (KHV): a review

The first outbreaks of a disease connected with high mortality of common carp and koi carp caused by koi herpesvirus (KHV) were reported in 1998 in Israel and in the United States. Since then, several cases have been confirmed all over the world. At present, this viral disease is considered to be one of the most risky factors affecting populations of common carp and koi carp. Affected fish become disoriented and swim erratically with high breathing frequency, swollen gills and partially local skin lesions. The virus was isolated from the tissues of fish showing signs of the disease and subsequently cultured on koi fin (KF-1) cells. Electron microscopic examinations revealed morphological signs identical with viruses of the family Herpesviridae. Analysis of virion polypeptides and gene DNA showed the differences between KHV and the well-known herpesvirus of cyprinids, Herpesvirus cyprini (CHV), and Channel catfish virus (CCV). Water temperature is a factor influencing the onset and severity of disease. Fish seem most susceptible at water temperatures of 18-28°C, no morbidities occur at 13°C and 30°C. At present, diagnosis of KHV is mainly based on detection of viral DNA by PCR method.