"Herpesviruses are a spectacular evolutionary success. They have been discovered throughout the spectrum of vertebrates and in at least one invertebrate. In nature, each is closely associated with a single host species, and the most extensively studied hosts are infected by several distinct herpesviruses. It is likely, therefore, that the 120 or so recognised species that currently constitute the family Herpesviridae represent a tiny portion of the number in existence. The host-specific occurrence of herpesviruses indicates that they have evolved with their hosts over long periods of time and are exquisitely well adapted to them. This view is supported by molecular phylogenetic studies and by the modest pathogenicity of herpesviruses in their natural settings. Examples of herpesviruses that exhibit high pathogenicity, either in humans or in farmed animals, are invariably the results of disequilibrium promoted by human activity."
Phylogenetic tree of 20 mammalian and avian herpesviruses, derived from comparing the sequences of 7 genes and 1 exon (adapted from ).
The three viral subfamilies (alpha, beta and gamma) differ in how restricted their host range is, what type of cells they can infect and establish latency in, and how long their replication cycle is.