Comparative studies of piscine and amphibian iridoviruses

A total of 30 iridoviruses collected from Australia, South-East Asia, North America, South America and Europe were characterised. With the exception o f the South-East Asian iridoviruses all viruses were found to belong to the genus Ranavirus. All viruses, except those originating from South-East Asi a, cross-reacted with antisera against epizootic haematopoietic necrosis vi rus (EHNV). Viruses or virus-infected cells were examined using electron mi croscopy, SDS PAGE, restriction endonuclease (RE) digestion, DNA hybridisat ion, and DNA sequencing. Data from RE digestion of genomic DNA, and from th e sequencing of PCR products indicated that the viruses generally grouped a ccording to their geographic and taxonomic (i.e. amphibian or fish) origin. The one exception to this was the viruses from the United Kingdom that gro uped with the North American ranaviruses. The differences between specified genomic regions were small. To assess the validity of the differences in s equence homology, similar studies were performed with different isolates fr om two viruses (EHNV and Guatopo virus (GV), collected from different anima ls at different locations and time). The sequence data showed complete homo logy for the isolates for any one virus over the 200 and 586 bp regions exa mined. Collectively, the data showed that the coding region for the major c oat protein (MCP) is stable for any one species (e.g. EHNV).