Megalocytivirus in ornamental fish

Megalocytiviruses (MCVs) are a group of closely related viruses that cause mass mortalities in both marine and freshwater aquaculture. MCV has a broad host range and can be present as a persistent subclinical infection in many temperate and tropical fishes. The type species for the genus is Infectious spleen and kidney necrosis virus (ISKNV). From the phylogenetic analysis, there are three ISKNV genotypes identified as red seabream iridovirus (RSIV), ISKNV, and turbot reddish body iridovirus (TRBIV). Infections with ISKNV and the closely related but distinct virus, RSIV are notifiable to the World Organisation for Animal Health. Outbreaks associated with ISKNV and TRBIV are difficult to prevent and control as there are no commercial vaccines, and individuals can be carriers for life with sporadic disease events resulting in considerable losses at farms. The focus of this chapter will be on pathobiology of ISKNV and TRBIV with a particular focus on ornamental fish as there is a separate chapter dealing with RSIV.