Lethal toxicity of arthropod iridoviruses to an amphibian, Rana limnocharis

Invertebrate Iridoviruses: A Glance over the Last Decade

Members of the family Iridoviridae (iridovirids) are large dsDNA viruses that infect both invertebrate and vertebrate ectotherms and whose symptoms range in severity from minor reductions in host fitness to systemic disease and large-scale mortality. Several characteristics have been useful for classifying iridoviruses; however, novel strains are continuously being discovered and, in many cases, reliable classification has been challenging. Further impeding classification, invertebrate iridoviruses (IIVs) can occasionally infect vertebrates; thus, host range is often not a useful criterion for classification. In this review, we discuss the current classification of iridovirids, focusing on genomic and structural features that distinguish vertebrate and invertebrate iridovirids and viral factors linked to host interactions in IIV6 (Invertebrate iridescent virus 6). In addition, we show for the first time how complete genome sequences of viral isolates can be leveraged to improve classification of new iridovirid isolates and resolve ambiguous relations. Improved classification of the iridoviruses may facilitate the identification of genus-specific virulence factors linked with diverse host phenotypes and host interactions.

Occurrence of an invertebrate iridescent-like virus (Iridoviridae) in reptiles

Viral isolates were obtained in 1998, 1999 and 2000 from the lung, liver and intestine of two bearded dragons (Pogona vitticeps) and a chameleon (Chamaeleo quadricornis) and from the skin of a frill-necked lizard (Chamydosaurus kingii) by using viper heart cells (VH2) at 28 degrees C. Electron microscopic examination of infected VH2 cells revealed the assembly of icosahedral iridovirus-like particles measuring 139 nm (side to side) and 151 nm (apex to apex). Negatively stained virus particles had dimensions of 149 nm (side to side) and 170 nm (apex to apex). Polymerase chain reaction (PCR) amplification of purified viral DNA with primers corresponding to the partial gene encoding the major capsid protein (MCP) of Frog viris-3 (FV-3), the type species of the genus Ranavirus, was unsuccessful. In contrast, primers corresponding to the partial MCP gene of Chilo iridescent virus (CIV; genus Iridovirus) amplified 500-bp products with 97% identity to the nucleotide sequence of CIV and 100% identity to the nucleotide sequence of Gryllus bimaculatus iridescent virus (GbIV), an invertebrate iridescent virus. Virus protein profiles analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and restriction fragment length profiles of purified viral DNA treated with the endonucleases EcoRI, HindIII and HpaII were identical to those of GbIV.