Comparative studies of iridoviruses: further support for a new classification

Changes in the classification of invertebrate iridoviruses (IVs) (Iridoviridae) have recently been proposed (Williams and Cory, 1994). The previous system of naming isolates according to the host and sequence of discovery (IV type 1, IV2, IV3, etc.) is not adequate for the purposes of taxonomy, since iridovirus isolates may infect many species, including hosts from diverse invertebrate orders. The new system of invertebrate iridovirus nomenclature, as with several other virus families, is based on geographical origin. Proposals have been made, based on DNA hybridization and other characteristics, by which invertebrate iridovirus isolates can be assigned to one of four recognized complexes, or considered as candidates for alternative assignations. This study reports comparative data on the DNA of 14 invertebrate iridovirus isolates used in the Williams and Cory study plus the two type vertebrate iridoviruses, frog virus 3 and flounder lymphocystis disease virus. DNA studies support the validity of assigning several isolates a common name and of grouping the known isolates into four complexes. The detection of such complexes is in broad agreement with previous serological studies. A previously undescribed isolate (San Miguel IV) obtained from the lepidopteran pest Anticarsia gemmatalis (Lep.: Noctuidae) has been initially characterized following the procedures recommended by Williams and Cory. DNA hybridization and Southern blot analysis identified this isolate as a new member of the Polyiridovirus complex. The San Miguel IV MSP gene was identified and a central fragment of ca. 719 bp was recovered by PCR amplification. The restriction endonuclease profiles (5 enzymes) of this isolate were distinct from others previously described.