Megalocytivirus

Megalocytivirus is a genus of viruses in the family Iridoviridae and one of three genera within this family which infect teleost fishes, along with Lymphocystivirus and Ranavirus. 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.

Taxonomy

The family Iridoviridae is divided into seven genera, including Chloriridovirus, Iridovirus, Lymphocystivirus, Megalocytivirus, Daphniairidovirus, and Ranavirus. 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). 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. • Megalocytivirus lates1, Scale drop disease virus • Megalocytivirus spagrus1, Red seabream iridovirus ==Pathology==

Pathology

Infection with these viruses produces a characteristic presence of enlarged basophilic cells within infected organs. == Structure and replication ==

Structure and replication

Megalocytiviruses are large icosahedral DNA viruses measuring 150-250 nm in diameter with a large single linear dsDNA genome. Uncoated viral particles subsequently translocate to the host cell nucleus, where a virally encoded DNA polymerase facilitates DNA replication. Viral DNA then leaves the nucleus of the host cell and a second stage of DNA replication occurs in the cytoplasm, forming DNA concatemers. Iridoviral DNA, unlike other DNA viruses infecting eukaryotic cells, is circularly permuted and exhibits terminal redundancies. == Transmission and epizoology ==

Transmission and epizoology

Transmission of megalocytivirus is believed to occur when a naïve fish ingests tissues from infected fish or via contaminated water. In addition, a 2008 study reported 10 aquarium fish species that tested positive for ISKNV in Korea. == Pathogenesis ==

Pathogenesis

As megalocytiviruses have only been recently identified and described, the pathogenesis of megalocytivirus infection is relatively poorly understood. Clinical signs associated with infection are nonspecific and may include appetite loss, uncoordinated swimming, lethargy, coelomic distention, darkening skin color, petechiae, fin erosion, and death. == References ==

Source: Wikipedia ↗

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