Koi Herpesvirus Highlights and Potential of Probiotics to Reduce or Even to Prevent Koi Herpesvirus Infection

Koi herpesvirus (KHV) is a highly contagious virus that causes high morbidity and mass mortality of koi carp (Cyprinus rubrofuscus Lacepède, 1803), common carp (Cyprinus carpio Linnaeus, 1758) and its ornamental (coloured) varieties. Koi herpesvirus disease (KHVD) is one of the major factors that cause sig¬nificant economic losses affecting both wild and cultured populations of common and koi carp worldwide. It is thought that there is no effective treatment for KHVD. The usage of vaccines for aquatic animals and water environments is limited, associated with the risk of viral reactivation and reversion to virulence. In Europe, for example, no commercial vaccine for KHVD is available. On the other side, probiotic additives are one of the most prospective, promising, and safe alternatives of drugs, that provide fish health benefits such as improvement of fish immune resistance and increased growth performance. This paper provides a thoroughgoing analysis of the knowledge about Koi herpesvirus and the disease, its distribution, and con¬ventional treatment methods. We discuss the potential of probiotics for improvement of growth rate and carp immune resistance, associated with the fish mucosal immune system as the first immune barrier.