Family: Iridoviridae

Subfamily: Alphairidovirinae

Distinguishing features

Viruses within the subfamily infect primarily ectothermic vertebrates, i.e., bony fish (superclass Osteichthyes), amphibians and reptiles. In addition, members of the subfamily display the following characteristics: (1) they, with the exception of SGIV, encode a DNA methyltransferase that methylates cystosine residues within CpG dinucleotides, (2) with the exception of some lymphocystiviruses, their genomes are generally smaller (103–140 kbp versus ~200 kbp) and display a higher G+C content (49–55% versus 28–48%) than those of betairidoviruses. 

Genus demarcation criteria

The three genera within the subfamily are distinguished by differences in sequence identity, phylogenetic relationships, host species, G+C content, and clinical manifestations of viral infection.