PROPOSALS FOR A NEW CLASSIFICATION OF IRIDESCENT VIRUSES

The need for comparative studies of iridoviruses to elucidate the rela tionships between them has been well appreciated. Sixteen iridoviruses , including type species from each of the four recognized genera of th e Iridoviridae, were compared by restriction endonuclease characteriza tion, hybridization to the major structural protein (MSP) gene of an i nvertebrate iridescent virus (IV) isolate at various stringencies, PCR amplification of the MSP gene region and by dot-blot hybridization st udies. The results broadly supported previous serological studies. The vertebrate iridoviruses, frog virus 3 (genus Ranavirus) and flounder lymphocystivirus (genus Lymphocystivirus), appeared distinct from one another and from the invertebrate isolates. Naming and numbering inver tebrate IV isolates according to history and host is no longer useful since IVs infect a number of species. A revised system, involving name s based on the geographical origin of the isolate is proposed, in line with other virus families. The large IVs of invertebrates represented by Vero Beach IV (previously IV3 or mosquito IV; genus Chloriridoviru s) showed little similarity to any other IVs. Members of the genus Iri dovirus, the small invertebrate IVs, fell into three distinct groups o f interrelated isolates. The largest group, containing the Plowden (IV 1), Tia (IV2), Nelson (IV9, IV10 and IV18), Aberystwyth (IV22), Srinag ar (IV24), Fort Collins (IV29) and Stoneville (IV30) iridoviruses, is named the Polyiridovirus complex. The Plowden iridovirus (IV1) is sugg ested as type species for this complex given the data available on its molecular biology. Based on previously published data, Timaru (IV16 a nd IV19) and Uitenhage (IV23) iridoviruses are also assigned to this c omplex. The second but smaller group is named the Oligoirido-virus com plex, which includes Dazaifu (IV6) as the type species and contains Nt ondwe (IV21 and IV28) on a tentative basis. Riverside IV (IV31) was di stinct from both of the other groups, and is proposed as a third compl ex, Crustaceoiridovirus.