Iridoviridae

Iridoviridae are a family of viruses all with dsDNA genomes. The family contains five genera: Chloriridovirus, Iridovirus, Lymphocystivirus, Megalocytivirus, and Ranavirus. Members of the Iridoviridae family infect mainly invertebrates, but also some vertebrate species such as fish and frogs. The genome is 150000-280000 nt. long. They have icosohedral symmetry. The virion is made up of three domains; an outer proteinaceous capsid, an intermediate lipid membrane, and a central core containing DNA-protein complexes. Some of the viruses also have an outer envelope.

Replication
Final packaging occurs in the cytoplasm but a stage of replication also occurs in the nucleus. Virus particles enter the cell and uncoating occurs. Viral DNA then travels to the host cell nucleus and is transcribed by host RNA polymerase II modified by the virus. Meanwhile host macromolecular synthesis is stopped. Parental DNA produces a genome, which is then the template for replication in the cytoplasm. Large concatamers of viral DNA are formed by recombination in the cytoplasm. The concatamers are then packaged and the virus is released either by budding out of the cell membrane or cell lysis.

Gene Expression
Transcription occurs in three stages; immediate-early, delayed-early, and late. Positive induction and negative feedback mechanisms exist in each stage, mediated by products of the other stages.

Pathogenesis
Little is known about the pathogenesis of iridoviruses. The pathogenesis is, however, temperature dependent and iridoviruses are thus confined to poikilothermic hosts.