Megalocytivirus

Megalocytivirus is one of five genera of viruses within the family Iridoviridae and one of three genera within this family which infect teleost fishes, along with Lymphocystivirus and Ranavirus. The megalocytiviruses are an emerging group of closely related dsDNA viruses which cause systemic infections in a wide variety of wild and cultured fresh and saltwater fishes. Megalocytivirus outbreaks are of considerable economic importance in aquaculture, as epizootics can result in moderate fish loss or mass mortality events of cultured fishes. The family Iridoviridae is divided into five genera which include Chloriridovirus, Iridovirus, Lymphocystivirus, Megalocytivirus, and Ranavirus. Megalocytivirus is the most recently added genus. Megalocytivirus isolates exhibit relatively few genetic differences and have been divided into three major groups based on genetic sequence data; these groups are represented by infectious spleen and kidney necrosis virus (ISKNV), red sea bream iridovirus (RSIV), and turbot reddish body iridovirus (TRBIV). RSIV and ISKNV are the best known of the megalocytiviruses. Song, et al. evaluated 48 Asian and Australian megalocytivirus isolates with regard to geographic location and genetic variation in the major capsid protein gene and developed a phylogenetic tree which divided the 48 isolates into three distinct clusters based on genotype. One of these clusters (genotype I) is widely distributed among several Asian countries, including 13 isolates from Korea, nine isolates from Japan, one from Thailand, one from China, and one from the South China Sea. In contrast, the other two genotypes had a smaller host range and were locally distributed. Genotype II megalocytiviruses infected freshwater fishes from Southeast Asia and Australia, whereas genotype III megalocytiviruses infected primarily flatfish in China and Korea.